Is 110°C too hot in 96°F ambient temps?

[linjam]

Your photo shows a temp of around 115-118°C. That is much higher than normal, for only 90C ambients, even if it's humid and the car is stationary.

I don't trust the mechanic's assessment that the current fan is "pulling well"... the vast majority of mechanics don't know how to tell good vs bad. As discussed in other threads, the clutch is an analog device, and varies infinitely between fully disengaged and fully engaged. Engagement is entirely based on AIR temp at the face of the clutch, not coolant temp. Obviously there are myriad variables which can affect this.

The ACM clutch is engaged almost all the time, so installing that will tell you pretty quickly if it was an airflow issue. Based on your description, it does sound like airflow, because when the electric fans turn on and/or the car is moving, the temps drop. If it were a bad t-stat or radiator, electric fans running would not help much; ditto for cruising at freeway speeds.

Side notes: If the t-stat is more than 7-10 years old, replacing proactively would be a good idea. If the radiator is original from 1992-ish, that wouldn't hurt either, but when it's removed to replace the electric fans+clutch, the radiator AND condenser should be cleaned thoroughly with compressed air. The OE twin electric fans are expensive; if you get ACM, the brackets from the original fans may need to be swapped to the new ACM motors. Also pressure test the cooling system and confirm it's tight to at least 1.2 bar; replace the cap if it isn't recent, ditto for the plastic reservoir if it's original.

And yes, the OE clutches are often mis-calibrated from the factory, which is ridiculous. If it turrns out your old clutch was bad, drop me a line if you want to sell it...

Thanks very much, Dave. I appreciate your input. See my reply to Gerry above for answers to some of your points, and I'll share with my mechanic, Marv, some of the thoughts here.

In addition, Marv tested the fan clutch at different rpms and temps with his hand (how easy it was to stop the fan). He said it was extremely inconsistent. Given I've replaced both radiator and thermostat in the last few years, I can only hope changing the fan clutch and getting both aux fans working properly will solve the problem.

Finally, I can't imagine all that heat in the engine compartment is good for all the other items in there. I don't like the idea of the ACM fan clutch drawing so much power, but nor do I like the idea of the Mercedes clutch causing premature wear of this rare engine and other components.

I'm happy to sell you the Mercedes clutch, Dave. I'll PM you.

 

[linjam]

It very well could be that your abnormally high temperature is caused by the bad aux fan, with the underlying problem either a fan clutch or a thermostat. My ACM clutch solved my issue completely. Just today, 91F, highest I see when stopped in traffic is 95F, with A/C blasting. Highly recommend ACM clutch - cheap and works well

Thanks, Kiev. hopefully replacing aux fans (one is bad, as I mentioned initially) and fan clutch will do the trick.

I am incredulous that Mercedes could ship an inferior operating vital piece of equipment like a fan clutch. Amazing.

 

[linjam]

On a related note, I have read (danger, Will Robinson) that coating/baking my headers and possibly exhaust in ceramic coating helps remove heat from the engine and exhaust, keeping things, including the engine compartment, cooler. Anyone have any thoughts/experience on this subject?

 

[gerryvz]

Thanks for your valuable input, Gerry. Much appreciated.

The radiator, condenser, and thermostat have all been replaced in the last 2-3 years, so that should eliminate them as possible culprits. My mechanic, Marv (he's the most old school mechanic at MB of Arlington and is the one most of the other guys go to when they need help) said the water pump was working normally.

Gerry, I'm no expert, but getting up to 115 Celsius, even in Houston summers, sounds pretty hot. I would think that level of heat would be hard on other components in the engine compartment as well, no?

In my case, the temperature would climb when moving slowly or not at all and would drop when moving more quickly. The night is was 65 Fahrenheit, this was the case, with the gauge reading between 108 and 82 Celsius -- pretty dramatic shift up and down, depending on vehicle motion or lack thereof.

Just because something has been replaced, doesn't mean it can't go bad quickly, or even out of the box. I have heard (and now have experienced) a bad Behr/Mahle thermostat on my G-wagen that lasted perhaps 25-30K miles and well under four years. Replacing it solved an overheating problem on my M104, with consistent temperatures in the 110-118C range when at high speed. See this post -- admittedly my symptoms and experience are different than yours, as I was experiencing the hottest temperatures at high speeds and high engine loads (i.e. going up hills). When sitting in a parking lot, my engine temps actually cooled down substantially due to the fan operation and the fan clutch. I could also make temps go down a bit by putting the interior heater on HI speed fan and HOTTEST temperature. This clearly indicated to me that there was a coolant circulation problem, which led me to replace the thermostat after just a few years. I had lived with the hot temps for more than 1.5 years.

Replacing the radiator and fan clutch (also a new fan clutch as of a few years ago, but original radiator) didn't solve the problem.

I also found in the diagnosis process, that the second-stage of the aux fan on the G-wagen was bad, caused by a bad temp sensor where it screwed into the top of the water pump/thermostat cover area on the engine.

Since your hotness is happening at low/slow speeds, I believe you do have a fan clutch problem. I had a similar issue with my M117 560SEC, and a new clutch solved it.

I am not a fan of the ACM clutch, and would always prefer a properly operating factory Horton clutch over the Chinese ACM product.

One thing, and this is a common misperception among owners: Having temps of 110+ IS NOT FATAL to the engine, nor is it going to create premature failure or stress on things. The pressure in the cooling system (and the coolant mixture with water itself) raises the boiling point of the coolant significantly, and this is why the "danger zone" of the indicated MB temps starts at 120C. I have run my E500 plenty at 105-115C temps in Texas, not to mention my G-wagen's M104 at 110-118C temps at high speeds, and they have not been adversely affected. 10-20 degrees is not going to make or break an engine, and not even necessarily kill the head gasket or other components prematurely.

Certainly if you overheat the engine, it's going to cause problems, but MB engines are robust and they are actually designed to run a bit hotter than many other engines of the era. This is because things (up to a point) are more efficient when the engine runs hotter, before reaching a point of diminishing returns that falls off rapidly.

So yes, I do not like and have never liked seeing my engines running at 110C plus, but I've also not freaked out about driving my G-wagen from my house into Washington DC many many times at 105-115C on the highway. If MB didn't think the engine should run at that temp, or could handle it over long periods of time, they would have designed the engine with a lower temperature envelope, and they would have had a lower red zone on the temperature display.

All this said, it is most definitely preferable to have the engine running at lower temps, and the 87-100C range is where I like to see things. But I have learned not to freak out (too badly) if I see 110-115C. YES, something is wrong and should be fixed if one is seeing 110C+ even in high 95+F ambient temps with the A/C on. NO, it's not going to destroy your engine.

Thanks, Kiev. hopefully replacing aux fans (one is bad, as I mentioned initially) and fan clutch will do the trick.

I am incredulous that Mercedes could ship an inferior operating vital piece of equipment like a fan clutch. Amazing.

I'm hoping that you have tested the thermal switch that activates the fan's second stage, based on the appropriate coolant temp, to ensure that it is not a culprit with regard to the fan operation being faulty.

It's been documented here on the forum in the fan clutch threads that many if not nearly all E500E fan clutches, including many new ones from Horton/Sachs that have been made in very recent years, have shipped from the factory defectively. It is a shame, but it is also a reality. This has only seemed to be a problem with the M119 clutches, as I have replaced them on my M117 and M104 and they've worked well (and replaced bad clutches on both cars).

On a related note, I have read (danger, Will Robinson) that coating/baking my headers and possibly exhaust in ceramic coating helps remove heat from the engine and exhaust, keeping things, including the engine compartment, cooler. Anyone have any thoughts/experience on this subject?

Back in 2010, when I re-did the top end of my M117 engine, I had both the exhaust manifolds and intake manifold ceramic coated. It is indeed supposed to cut down heat, but I have never detected a MEASURABLE reduction in engine bay temperature due to this. My thermal "butt dyno thermometer is admittedly less sensitive than others, but I've yet to see a thread from anyone on this forum raving about how their newly coated exhaust manifolds have allowed them to instantly touch them upon engine shutdown, or how their engine bay's soft parts have been less "cooked" over time. YMMV, but I'm somewhat skeptical and will never have this process done again.

 

[gsxr]

In addition, Marv tested the fan clutch at different rpms and temps with his hand (how easy it was to stop the fan). He said it was extremely inconsistent.

That "hand test" method itself is inconsistent, due to the reason I described earlier... a clutch can be partly engaged. It sounds like all he confirmed was that the clutch was not fully engaged, which may or may not be normal depending on the conditions present during the test.

The ACM clutch is useful as a tool to "force" airflow and see what happens with only the clutch is changed. I agree that it's really sad that Sachs/Horton has been supplying mis-calibrated clutches to MB for years. In one of the old posts from Klink, he reported having to go through 5-10 different new clutches before finding one that worked normally. It took me years to figure this out on my own, and eventually learned how to test more scientifically using an optical tachometer on the fan blade.

Gerry is correct that 110-115C is not fatal to the engine. There's a reason the red zone is at 120C. However, safe operation up to 120C also requires the rest of the cooling system to be in working order, AND the correct mix of antifreeze, to prevent boiling at temps under 120C. Still, seeing 110C+ on the gauge is not normal, and unless traveling through Death Valley in August, generally means something ain't right. This also assumes the gauge is accurate, and the electric fans are running on high speed above the 107C cut-in point.

BTW, I agree about the additional heat not being good for anything. On all my cars, after parking in the garage on warm days, I open the hood. No point in letting all that heat cook rubber & plastic items.

 

[linjam]

Just because something has been replaced, doesn't mean it can't go bad quickly, or even out of the box. I have heard (and now have experienced) a bad Behr/Mahle thermostat on my G-wagen that lasted perhaps 25-30K miles and well under four years.

I also found in the diagnosis process, that the second-stage of the aux fan on the G-wagen was bad, caused by a bad temp sensor where it screwed into the top of the water pump/thermostat cover area on the engine.

I am not a fan of the ACM clutch, and would always prefer a properly operating factory Horton clutch over the Chinese ACM product.

It's been documented here on the forum in the fan clutch threads that many if not nearly all E500E fan clutches, including many new ones from Horton/Sachs that have been made in very recent years, have shipped from the factory defectively.

Back in 2010, when I re-did the top end of my M117 engine, I had both the exhaust manifolds and intake manifold ceramic coated. It is indeed supposed to cut down heat, but I have never detected a MEASURABLE reduction in engine bay temperature due to this. My thermal "butt dyno thermometer is admittedly less sensitive than others, but I've yet to see a thread from anyone on this forum raving about how their newly coated exhaust manifolds have allowed them to instantly touch them upon engine shutdown, or how their engine bay's soft parts have been less "cooked" over time. YMMV, but I'm somewhat skeptical and will never have this process done again.

Thanks, Gerry.

I'll see how the fan clutch and aux fan replacements do in solving the problem before worrying about the thermostat, expecially given the nature of my symptoms.

One of my two aux fans is running very slowly, so I am just replacing both. The temperature sensor would not cause just one to run slowly, would it?

Given the problems with the factory clutches and that others here seem happy with their ACM clutches, I'd rather have a cooler engine bay and peace of mind over a far more expensive factory part which doesn't work properly. Fairly extraordinary that such an important part could continue to be allowed to ship from the factory like that.

I'll do more research on the ceramic coatings.

Jamie

 

[linjam]

That "hand test" method itself is inconsistent, due to the reason I described earlier... a clutch can be partly engaged. It sounds like all he confirmed was that the clutch was not fully engaged, which may or may not be normal depending on the conditions present during the test.

Thanks, Dave.

He believed the hand test showed it to be weak at a time when it should have been fully engaged.

I feel I've no opportunity but to go with the ACM clutch, given the factory clutch issues.

 

[gsxr]

One of my two aux fans is running very slowly, so I am just replacing both. The temperature sensor would not cause just one to run slowly, would it?

The 2 electric fans should run at identical speeds. And there are only 2 speeds, low (via resistor) or high.

Other chassis in the 90's (i.e. 140, 210) have more speeds available. Newer chassis (i.e., 211) have a yuge single electric fan that is variable speed, and replaces both the mechanical viscous clutch as well as the "auxiliary" fans.

 

[Bill Walsh]

I have about 10,000 miles on a new MB fan clutch and since replacing it my car has frequently exceeded 100 degrees when using the A/C or climbing the hills of San Francisco. A few weeks ago my Indy determined the fan clutch was bad and today replaced it at no charge. MB stepped up and provided a new clutch.

 

[linjam]

I have about 10,000 miles on a new MB fan clutch and since replacing it my car has frequently exceeded 100 degrees when using the A/C or climbing the hills of San Francisco. A few weeks ago my Indy determined the fan clutch was bad and today replaced it at no charge. MB stepped up and provided a new clutch.

From what we are learning about the Mercedes 119 clutches, they should replace them all with a new production run. It's called a "recall".

 

[BTR]

Comprehensive thread on cooling system issues! Pertinent for me, as I recently replaced my original fan clutch with an ACM unit and flushed the coolant. A few data points follow below...hopefully useful for others.

Exhibit A - Normal Highway Cruising. Coolant temp stays near “9 o’clock” (~85C) under pretty much all ambient temps (seen up to probably a humid low 90F’s this spring) while maintaining about 80mph, with or without A/C on. Same observations before and after recent cooling system service.

Exhibit B - Bad Traffic Jam.
With ice-cold A/C at full tilt (HVAC temp wheel generally always set to ~72F, auto fan spd), close to 90F ambient and humid, NYC stop and go over maybe 10 miles at least (loveee the Cross Bronx Expressway!), temps creep to about midway between 120 and the next lowest tic mark on the temp gauge (is midway 110C??) and stay here until steadily resuming more normal speeds (>30 mph) with normal temps following shortly. I initially thought 110C was abnormal (temp never varies in my other newer cars once warmed up), but not after reading this thread. This observation was taken after original failed fan clutch was replaced with a new ACM unit, in conjunction with a coolant flush a few weeks ago. Previously, temps would reach scarily close to 120C in traffic, but only with A/C on - maybe max 105C with A/C off - even during the somewhat cooler early spring (~70F ambient).

Thankfully, I’m cruising on higher speed highways the majority of the time, but the car needs to survive an occasional jaunt through hellish NYC traffic in equally bad summer heat.

 

[a777fan]

Hey BTR! Definetley check your fuse on the aux cooling fans to make sure they are functional. They should kick on ‘high’ at 107C on the gauge, and I always note a noticeable reduction in temps when they do, even at a standstill. Environmental conditions certainly play a large part in the fans effectiveness, but it wouldn’t hurt to pop the fuse box cover and check to make sure.

 

[8899]

Exhibit B - Bad Traffic Jam.
With ice-cold A/C at full tilt (HVAC temp wheel generally always set to ~72F, auto fan spd), close to 90F ambient and humid, NYC stop and go over maybe 10 miles at least (loveee the Cross Bronx Expressway!), temps creep to about midway between 120 and the next lowest tic mark on the temp gauge (is midway 110C??) and stay here until steadily resuming more normal speeds (>30 mph) with normal temps following shortly. I initially thought 110C was abnormal (temp never varies in my other newer cars once warmed up), but not after reading this thread. This observation was taken after original failed fan clutch was replaced with a new ACM unit, in conjunction with a coolant flush a few weeks ago. Previously, temps would reach scarily close to 120C in traffic, but only with A/C on - maybe max 105C with A/C off - even during the somewhat cooler early spring (~70F ambient).

That's interesting. At what point are your electric auxiliary fans turning on?

 

[gsxr]

With ice-cold A/C at full tilt (HVAC temp wheel generally always set to ~72F, auto fan spd), close to 90F ambient and humid, NYC stop and go over maybe 10 miles at least (loveee the Cross Bronx Expressway!), temps creep to about midway between 120 and the next lowest tic mark on the temp gauge (is midway 110C??) and stay here until steadily resuming more normal speeds (>30 mph) with normal temps following shortly. I initially thought 110C was abnormal (temp never varies in my other newer cars once warmed up), but not after reading this thread.

Your photo indicates a temp of roughly 107C, give or take a bit. This is higher than normal, IMO, but not dangerous. At this point it depends if you want to keep trying to figure out what isn't right, or just be happy that temps are reasonably safe. Since this only happens at low vehicle speeds (idling in traffic), I would confirm that your electric fans are working on low speed when AC is on (this thread, or others, detail exactly when the electric fans should be running on low or high speeds). Since the temps remain at ~85C at high speeds, in any ambient temp with or without AC, it isn't likely you have radiator or condenser fins plugged with debris, or radiator/t-stat issues.

Previously, temps would reach scarily close to 120C in traffic, but only with A/C on - maybe max 105C with A/C off - even during the somewhat cooler early spring (~70F ambient).

120C is not normal. You should never see anywhere near 120C in 70F ambients. Ever. Sounds like your old fan clutch was not engaging properly, and the ACM improved things. Still, you should definitely check the electric fans, but you may have something else going on, since your temps are still not as low as they should be IMO.

 

[msq]

Comprehensive thread on cooling system issues! Pertinent for me, as I recently replaced my original fan clutch with an ACM unit and flushed the coolant. A few data points follow below...hopefully useful for others.

Exhibit A - Normal Highway Cruising. Coolant temp stays near “9 o’clock” (~85C) under pretty much all ambient temps (seen up to probably a humid low 90F’s this spring) while maintaining about 80mph, with or without A/C on. Same observations before and after recent cooling system service.

Exhibit B - Bad Traffic Jam.
With ice-cold A/C at full tilt (HVAC temp wheel generally always set to ~72F, auto fan spd), close to 90F ambient and humid, NYC stop and go over maybe 10 miles at least (loveee the Cross Bronx Expressway!), temps creep to about midway between 120 and the next lowest tic mark on the temp gauge (is midway 110C??) and stay here until steadily resuming more normal speeds (>30 mph) with normal temps following shortly. I initially thought 110C was abnormal (temp never varies in my other newer cars once warmed up), but not after reading this thread. This observation was taken after original failed fan clutch was replaced with a new ACM unit, in conjunction with a coolant flush a few weeks ago. Previously, temps would reach scarily close to 120C in traffic, but only with A/C on - maybe max 105C with A/C off - even during the somewhat cooler early spring (~70F ambient).

Thankfully, I’m cruising on higher speed highways the majority of the time, but the car needs to survive an occasional jaunt through hellish NYC traffic in equally bad summer heat.

Had similar readings/situation (maybe not quite as high temp) when I first got my car and was idling w/A/C on an outside temp maybe in the high 60'sF (I forgot exact temp). With some troubleshooting help from @gsxr I figured out:

- fuse in electric fan relay needed replacement
- once that was done I did the "shorting the fan test" to make sure it worked - it did
- evac & refill A/C with new R134 (the pressure was too low and it was a number of years since that had been done)

Once I did the above everything seems fine and I don't see temp anywhere near the high you show in the pic. Don't underestimate the 3rd point above, since apparently if pressure in the system is not high enough, the electrical aux fans that should go on with A/C will not go on. These cars seem to run hotter than I would normally be comfortable with anyway but I think between their design parameters and the potential fan clutch issues, that is what you get. You could consider the "cool harness" (simple plug in) if you want the car to run cooler. There is info on that in threads here. I would not consider that until/unless all other systems in cooling system running as designed.

 

[BTR]

Thanks @a777fan, @8899, @gsxr and @msq for your helpful feedback. Excellent illustrations of electric fan diagnostics earlier in this thread will certainly help me diagnose any electric fan issues this weekend...sounds like an easy fix if there is something wrong.

I know the electric fans definitely work, but unsure if they are alternating between low and high speeds when running, as designed. Interesting point about A/C pressure, @msq. Will now check prior owner’s service records for A/C servicing.

@gsxr before I replaced the fan clutch after the needle first shot up near 120C (when I first used A/C in traffic as ambient temps warmed this spring), I made a habit of turning off A/C and running the heat to keep the motor cool. Even today, engine temps stay around 85-100C in traffic with no A/C and high ambient temps.

 

[gsxr]

BTR, based on what you describe, I'm very suspicious your electric fans are not working on LOW speed (in addition to your old clutch not engaging). Check for both low + high speed operation though. The fans should have kicked on high speed with engine temps over 107C, which should have pulled engine temps down even with a dead mechanical clutch.

About the AC, if it's blowing cold when it's hot outside, the pressures should be plenty adequate to trigger the switch (unless of course the switch is bad, which is uncommon). msq was possibly running into difficult testing due to low ambient temps back in springtime, which correlate to lower pressure in the system when AC is running.

 

[Kyiv]

Thanks @a777fan, @8899, @gsxr and @msq for your helpful feedback. Excellent illustrations of electric fan diagnostics earlier in this thread will certainly help me diagnose any electric fan issues this weekend...sounds like an easy fix if there is something wrong.

I know the electric fans definitely work, but unsure if they are alternating between low and high speeds when running, as designed. Interesting point about A/C pressure, @msq. Will now check prior owner’s service records for A/C servicing.

@gsxr before I replaced the fan clutch after the needle first shot up near 120C (when I first used A/C in traffic as ambient temps warmed this spring), I made a habit of turning off A/C and running the heat to keep the motor cool. Even today, engine temps stay around 85-100C in traffic with no A/C and high ambient temps.

I can confirm that if AUX fans work properly, you'll see 110C briefly and then temp, within a minute or less will descend to 105C even in the hottest, stop-and-go environment. My actual experience over 4 years. You'll hear the aux fans for sure, when they are working. The A/C in my case (non-working fan clutch) did not make any significant difference. You should see 110C for brief moments with properly working aux fans

CORRECTION: when aux fans kick in at 107, the temp is brought down to, I think, 97-98C in about a minute, not 105C as I've stated above. Again with a non-working fan clutch

 

[BTR]

Electric fans are definitely running intermittently with A/C on, at normal operating temps of under 100C. Fans seem to remain running while idling as temps hovered around 100C (first tic mark). I imagine I observed only the low speed setting.

Left car idling for a while and tried mimicking traffic-like conditions today, however, weather and traffic today are too perfect, thus not ideal for high temp testing - a Catch 22! Temps didn’t rise over 100C. So, when awful humidity inevitably returns (probably like, tomorrow), I’ll road test the functionality of high speed fan mode.

In the interim, enjoying additional horsepower from a ‘92 LH module with WOT functionality I purchased from @gerryvz, which I finally got around to installing this morning.

Should have mentioned...subject in question is the Moonstone Grey ‘95 .034 which I found on this forum, and purchased three months ago out of Olympia, Washington. My first W124, and really loving it

 

[Rouven036]

Yes, this is the switch and you have to short the wires connecting to the leads of the switch (the wiring from the chassis side). Thus shall switch on the aux fans with ignition on/engine running.
Also I had a bad wiring connection at the pre resistor behind the left head light. Check my owners thread, it's on the last or second last page...

 

[a777fan]

Should have mentioned...subject in question is the Moonstone Grey ‘95 .034 which I found on this forum, and purchased three months ago out of Olympia, Washington. My first W124, and really loving it

So YOU are the lucky one who nabbed it. I heard it was in pretty nice shape. Start an owner thread!

 

[gsxr]

So YOU are the lucky one who nabbed it. I heard it was in pretty nice shape. Start an owner thread!

That one looked fantastic, and the color combo/options were unicorn-y. Great score. FS thread here with pics:
https://www.500eboard.co/forums/ind...-moonstone-gray-gray-113kmi-4500-pacnw.12409/

 

[BTR]

Turned out to be in good condition, as expected of a well maintained car in an ideal climate. Seller, who was the second owner, was great to deal with. He had bought the car in 2003, Star Certified from MB Bellevue, which was the original selling dealer, serviced it at MB dealers and provided stacks of records from day 1 of his ownership, plus complete original books with dealer stamps from original delivery date in 1995. Also swung by MB Bellevue the day I bought the car, and happened to bump into the guy who sold it new, and pre owned in 2003 - a die hard 124 and Mercedes enthusiast who spotted my arrival, remembered the car for its rare color and was kind enough to give me a VMI and fresh original Barrier Bellevue plate frames. Interestingly, he daily drives a 300D with a 500E sportline interior.

Finally found traffic conditions again this evening ....definitely observed normal operation of the high speed fan kick-in at ~107C, shortly after pulling into my city garage, which turned off as needle settled down to 100C as I let car idle with A/C on. Low speed fan turned on shortly thereafter. The photo above was during perhaps more extreme conditions - longer duration traffic midday, with higher ambient temps and high humidity - which I had also experienced on one or two other occasions. I'm beginning to think this observation of sustained high ~107C temps is normal under such conditions, which are probably considered extreme. Is this normal in very hot and humid (tropical-like?!) conditions, with limited airflow (bumper to bumper stop and go urban traffic jam)?

 

[gerryvz]

This has been discussed ad nauseum here on the forum, but 107C indicated and sustained temps is NOT and is NEVER normal. When the car is moving, honestly even in hot and humid temperatures the temp gauge should never even see the 100C hash mark or above. At stop signs and extended idling, it can and will climb, and even temps of 105C+ can be reached, but a properly operating second-stage aux fan should mitigate that back down to the 90C range, and it should be a continuing cycle.

Temps can and will be higher by ~3-5C when the A/C is on, and I found living in Texas that temps can also be elevated a bit when driving in hot (95F and higher) and very humid (80-90+ percent) conditions. However, even in these conditions, temps when the car is moving of more than 100C indicates that something is wrong with the cooling system.

I lived with a high-temp condition on my G320 (M104 engine) for nearly 1.5 years -- this was 110C+ temps for everyday driving, even when the truck was moving. My situation turned out to be a bad thermostat, which had last been replaced just 3 years earlier. I can't make my G-wagen get above 95-97C indicated now, after replacing the thermostat, even in hot (90+F) ambient temps. Normal driving temps are 87-90C indicated temperature, even with the A/C on, when the truck is moving.

What I learned through all of this, as a general rule of thumb, was the following:

Cooling temp problems are either caused by airflow issues, or coolant circulation issues.

Airflow-related components that can cause problems are: aux fans and associated temp sensors, relays, fuses, etc.; fan clutch; radiator (if externally clogged with bugs/detritus, or otherwise physically/externally blocked from flowing air efficiently by debris); or fan shroud (directs air properly)

Coolant circulation components that can cause problems are: thermostat; radiator (if old and blocked/clogged internally with scale inside the tubes, or leaking, etc.); water pump (impeller not circulating coolant efficiently); coolant expansion tank cap (not maintaining system pressure).

a) If you are hitting elevated temps at speed, when the car is moving, then you likely have a coolant flow problem. Meaning that coolant is not reaching the radiator as it should be, to get cooled. If you can see the temp go down by a few degrees if you turn on the interior heater full blast, this is another indicator that coolant is not being properly circulated through the coolant system. This was my problem, and it was caused by a faulty thermostat not opening fully and allowing coolant to enter the radiator as it should have.

b) If you are hitting elevated temps at low speed (but temps are more reasonable while driving at speed), then you likely have an airflow problem, whereby the fan clutch is not working and circulating air properly, or the aux fan stages (one or both) are not kicking in to circulate more air over the radiator to cool things down. I also had this problem in my G-wagen, caused by a faulty aux fan coolant temp sensor screwed into the intake manifold (it didn't mitigate the thermostat problem, but it did help keep a lid on temps when I would idle in parking lots and at traffic lights).

Cheers,
Gerry

 

[gsxr]

I'm beginning to think this observation of sustained high ~107C temps is normal under such conditions, which are probably considered extreme. Is this normal in very hot and humid (tropical-like?!) conditions, with limited airflow (bumper to bumper stop and go urban traffic jam)?

In addition to what Gerry said. I think you are kind of at the limit of "normal" under semi-extreme conditions, IF the temps never go above ~107C, and it's hot/humid/90F+ ambients stuck in traffic. This also assumes the temps drop under 100C when cruising at 45+mph in the same ambient conditions.

Just to confirm - both low and high speed electric fans are working, AND you have an ACM clutch which is roaring away. Correct? Next thing I'd check for is dirt/debris trapped between the radiator and condenser (also, between the lower part of the electric fan shroud and condenser). This is a common issue and a real PITA to fix as to do it properly requires pulling the radiator, then using compressed air & a vacuum to clean all the debris out. At that point, if the radiator is old/original, a new one might be a good idea as preventive maintenance. Or you can just live with ~105C temps for a few months in summer, as long as it runs cool (<95C) the rest of the year.

 

[BTR]

107C indicated and sustained temps is NOT and is NEVER normal. When the car is moving, honestly even in hot and humid temperatures the temp gauge should never even seen the 100C hash mark or above. At stop signs and extended idling, it can and will climb, and even temps of 105C+ can be reached, but a properly operating second-stage aux fan should mitigate that back down to the 90C range, and it should be a continuing cycle.

High temps were observed in probably close to 100% humidity and high ambient temps (~90F), on heavily congested urban "expressways" with "parking lot" or "stop sign-esque" traffic conditions (more STOP than GO, @gerryvz).

In addition to what Gerry said. I think you are kind of at the limit of "normal" under semi-extreme conditions, IF the temps never go above ~107C, and it's hot/humid/90F+ ambients stuck in traffic. This also assumes the temps drop under 100C when cruising at 45+mph in the same ambient conditions.

Just to confirm - both low and high speed electric fans are working, AND you have an ACM clutch which is roaring away. Correct?

Yes, @gsxr - temps return to normal (~85C) fairly quickly after driving at sustained speeds of at least 30 MPH for a few minutes or less, in all ambient conditions I have encountered while driving this car. I confirmed that both low and high speed electric fans are operating properly, in accordance with descriptions of such earlier in this thread. Engine fan certainly roars away as engine speed climbs from idle, with a month-old ACM clutch.

As always, your insights are much appreciated. Hopefully this serves as an "extreme conditions" data point helpful for others, or maybe will even lead to discovery of other airflow issues (i.e., deeply-jammed debris). However, I believe the only airflow issues were other cars and/or large semi's surrounding my E420.

 

[gerryvz]

As long as the temps are going down within a couple of minutes when you are moving, then you should be OK, and that would indicate to me that you have coolant going through the radiator. If you are sitting in or having stop-and-go traffic on a hot/humid day, with the A/C going, it would not be odd to see temps of 107-110C indicated. I certainly experienced this when I lived in Houston, and it happened during the solid 6-7 months (May-October) of the year when temps would be 90F or higher.

For my E500, I also noticed a big change when I moved to Maryland in late 2017 -- even when it is 90F+ outside, we don't generally have the humidity that they have in Houston, and I never see temps above 105C in the hottest weather (stop and go, or idling in a parking lot), and I never see temps higher than the 100C hash mark when I'm driving at speed 80-90 MPH, when I can.

Same for the years (2003-2008) before I lived in Houston, when I was in Portland, Oregon, which is much more temperate. I never saw temps above 100C (even idling) when I lived there.

Humidity can play a significant role in operating temps.

 

[kwontumspeed]

Forgive me if it has already been mentioned, as I did not read every post in this thread, but I had noticed lately that my temps were higher than usual but nothing concerning that would launch me into troubleshooting mode. At speeds in hot Atlanta days the gauge read a smidge above 100. It would eventually pop down below the tick mark but hovered in that area as the new norm. In traffic jam ups it would creep higher, but the cooling system worked as you could see it cycle through the high speed fans, etc.

Well today, for whatever reason, I thought perhaps it was the gauge since I noticed that my gas gauge would be slow to "wake up" on some cold starts. I gave that area of the dash a couple of good smacks and my temp gauge is now reading much more normally than before

 

[nocfn]

I have an aftermarket Behr in my C126 and it does come on strong here in Houston and sometimes I think my gauge is stuck at 82C