Viscous Fans on running on high (80-85c engine temp)

[Matin]

Hi Guys,

Just for some background, I changed my viscous fan a couple of months ago -

I'm not sure whether this is normal or not, however, I have noticed that my car has it's viscous fans running at high speed when the engine temp of the car is normal.

Yesterday the temp here was 17c, engine temps were around 80-85 max, however, I could hear the viscous fan whirring loud when I pressed on the accelerator.

Is this normal behaviour? If not, does anyone know why this would be happening? Could be the fan resistor?

It feels like it's sucking quite a-lot of power out the car - if it's normal then it's okay, however, if not, I'd like to get it fixed!

Cheers,
Matin

 

[nocfn]

My experience, aftermarket fans engage a few degrees earlier in the process. If other things like a weak resistor, frayed corroded 10g wiring to the fan then that could be an issue as well. please note, I replaced my C126 with aftermarket BEHR, and it comes on a few degrees sooner than stock. My E500 was replaced with MB fan, and I did the rewire and replacement of the fan resistor, and it comes on normally. In 94F heat, it still creeps to 100 at stop lights under high humid Houston heat but drops to the 83 range in seconds.

 

[gsxr]

Matin, is your viscous fan clutch OE Sachs/Horton, or aftermarket (ACM, Vemo, etc)? Is it original, or has it been replaced? If you aren't sure what's in the car, can you post a photo?

The OE clutch should generally not be engaged at 17°C/60°F ambients and 80-85°C coolant temps, especially if the AC is off.

The viscous fan is fully mechanical and is not affected by the resistor in the twin electric fan circuit. Viscous and electric fans are completely separate.

 

[Melville]

Not likely but it’s possible your temp gauge is inaccurate and reading lower than actual temperature. If you have a temperature laser gun then use that on a black hose to check if the temperature indicated by the gun is about the same as the gauge.

 

[Matin]

Hi Guys,

Thanks for the replies. The clutch was replaced with a FEBI unit.

I don’t have a laser gun to check the temp of the engine and compare, I’ll see if I can pick one up for cheap.

 

[gsxr]

Matin, if it's a FEBI clutch, it's likely engaged almost all the time. This isn't normal for OE, but nearly every aftermarket "thin" clutch I've seen (ACM, Vemo, etc) are calibrated differently. I don't like them being engaged in cool weather so I don't use them, but in a hot climate it may be ok. The ACM clutch I tested would disengage around 4500rpm, about 1000rpm higher than the Sachs/Horton. I tested a Vemo clutch that never disengaged and spun to redline, which I really didn't like.

Note that Febi doesn't manufacture the clutch, they rebox items like this. Were there any markings to possibly indicate who made it?

 

[gerryvz]

It’s really best just to go with the $$$ factory clutch. Spend the money and be done with it.

 

[gsxr]

...but some of the factory clutches arrive mis-calibrated and don't engage fully until engine temps are high enough to cause most people to wig out.

Currently there isn't a good OOTB solution; except maybe running the OE clutch in winter and aftermarket in summer?

 

[Matin]

I’m afraid I’m not sure where it’s made. I don’t have the box anymore, seeing as it’s Febi, most likely made in China...

Thing is, I’ve only started noticing it after the temps here in the UK have started to heat up.

It feels as if the car gets hot (90-92c), clutch engages, but stays engaged even though the temps have gone down to a reasonable temp (80-85). The viscous just stays in high all the time after it has engaged once.

Any thoughts on any testing I can do or the best course of action here? Changing the clutch again would be the last option as it was a real nightmare to change last time.

Thanks

 

[JC220]

How old is the thermostat Matin? I find they dont last more than 3 or 4 years before they start to open sooner and reduce engine temps.

I dont see a problem with the viscous fan being engaged and if the thermostat was operating correctly the engine temp should not dip below 87c .

If it were my car I would leave the functioning fan well alone and renew the thermostat with a genuine MB or Wahler item

 

[gsxr]

Matin, there isn't much you can do at this point, either live with it as-is, or replace with something else (which may have other issues, as described previously).

The t-stat begins opening around 80C, IIRC, so you may see temps as low as 80C on the gauge - this is normal. But I'd expect any aftermarket "thin" clutch to be fully engaged at temps above 80C, unless perhaps if ambient temps are very cold (freezing/winter).

 

[JC220]

The t-stat begins opening around 80C, IIRC, so you may see temps as low as 80C on the gauge - this is normal.

I have to say this is not my experience regarding the thermostats. They should not allow the coolant temps to dip as low as 80c at any point. If it does, it is a tired stat in need of replacement. As they worsen the temps will go down to 70c or there abouts, in particular at 60mph or so with alot of air flow. Slow warm up time is also signs of a tired stat.

They are inexpensive so if it hasn't been changed in say the past 2 years, I would get a new one

 

[gsxr]

I've had some old/defective t-stats allow coolant temps down in the 70C range, which is definitely too low... mostly a problem in winter, as it takes forever to reach operating temp. IME, that is the typical symptom of a failing t-stat, taking way too long to reach operating temperature (80C+).

Most of my M119's hang around 85-90C most of the time, but I wouldn't worry about an indicated 80C if the engine reaches 80C quickly and doesn't drop below that under normal circumstances. Shoot, there are people who wring their hands at 87C and install CoolHarnesses™ trying to fix the 87C "overheating". LOL.

 

[Matin]

How old is the thermostat Matin? I find they dont last more than 3 or 4 years before they start to open sooner and reduce engine temps.

I dont see a problem with the viscous fan being engaged and if the thermostat was operating correctly the engine temp should not dip below 87c .

If it were my car I would leave the functioning fan well alone and renew the thermostat with a genuine MB or Wahler item

Hey Joe, the thermo stat is brand new. It was replaced around 6-8 months ago with a genuine MB part.

Looks like from reading the posts from you guys, it’s best to leave it alone as it’s operating how it should do as an aftermarket clutch.

The temps on the car are great, it doesn’t reach super high temps, probably 100C maximum on a 25-30c day in traffic which is pretty nice, just a shame about the clutch engaging and staying engaged when temps are returned back to normal, which obviously sucks power from the car.

I’ll put up with it..for now.

Thank you all for the help as usual!

 

[gerryvz]

A new thermostat is not a 100% guarantee that it is good. I recently had to replace a thermostat on my G-wagen that had been replaced just three years before.

I am also suspecting that the thermostat on my E500 (which I replaced a few years back, and documented here on the forum with a HOW-TO) is also now going bad, so I will replace it again as well.

These are aftermarket Behr/Hella branded thermostats, not crap parts. I believe the quality of even name-branded thermostats is quite poor, and the thermostats are either not working correctly out of the box, or are going bad after just 2-3 years (as JC says).

Cheers,
Gerry

 

[JC220]

A new thermostat is not a 100% guarantee that it is good. I recently had to replace a thermostat on my G-wagen that had been replaced just three years before.

I am also suspecting that the thermostat on my E500 (which I replaced a few years back, and documented here on the forum with a HOW-TO) is also now going bad, so I will replace it again as well.

These are aftermarket Behr/Hella branded thermostats, not crap parts. I believe the quality of even name-branded thermostats is quite poor, and the thermostats are either not working correctly out of the box, or are going bad after just 2-3 years (as JC says).

Cheers,
Gerry

I agree on all counts! Yes lately I have found thermostats to have a short life for some reason. Some are good for only a few months and others last a year or 18 months then I see the temp drop and warm up time increase. I must have bought 6 or 8 stats last year alone.

I either buy genuine or Wahler typically. It is usually Wahler in the MB box anyway. I did also get a Gates brand stat for an m104 and it appears to be holding up well.

80c in my opinion is a trifle low. My 500E has an ACM clutch which is engaged most of the time (doesn't bother me) and my temp quickly gets to 87 approx (1 - 2 miles fully at temp) and never dips back down again unless the motor is shut down. Doesn't matter if the fan is engaged and I can hear it - temp stays pegged solid at around 87c.

 

[Kyiv]

@gerryvz what symptoms are you noting that make you suspect that your thermostat in E500 is going bad?

 

[gerryvz]

@gerryvz what symptoms are you noting that make you suspect that your thermostat in E500 is going bad?

When I start up from a cold start, the temp starts out at 80C, and rises to an appropriate 85-87C after running the far for a number of miles. Then, after say 10-12 miles at 85-90C, the car will "break through" the appropriate 85-90C barrier, and start getting a bit hotter, in the 100-105C range (with the A/C running). This is high-speed freeway driving, and in ambient temps of 75-95F. At lower speed driving, it will go back down to the 85-95C range which I think is fine.

Both stages on the aux fans are working. I have a fan clutch installed from a 1992 500E that had ~55,000 miles on it, which I replaced about 5-6 years ago. I never hear the cluch roar. I have a brand new MB factory clutch in the box but have not installed it yet on my car.

105C doesn't wig me out though, like I know it does some folks. Radiator is near-new (2013, but not a lot of miles on it), and thermostat was replaced in 2015 (even fewer miles on it).

 

[gsxr]

... in the 100-105C range (with the A/C running). This is high-speed freeway driving, and in ambient temps of 75-95F. At lower speed driving, it will go back down to the 85-95C range which I think is fine.

Both stages on the aux fans are working. I have a fan clutch installed from a 1992 500E that had ~55,000 miles on it, which I replaced about 5-6 years ago. I never hear the cluch roar.

^^^ These symptoms are what I'd expect with a fan clutch that is freewheeling... not related to the thermostat.

 

[JC220]

@gerryvz what symptoms are you noting that make you suspect that your thermostat in E500 is going bad?

I'm not Gerry obviously but maybe he wont mind me pitching in.

You really only know what a healthy thermostat is like when you have one! Ie, it is easy to buy a car with a tired stat and never notice that it is not up to snuff. How to spot it?

Warm up time should be quick. In any of my m104s or m119s they are fully up to temp after driving only 2 or 3 miles. Aka less than 3 - 5 mins temp is up to 87c. Any longer than that is suspect.

The operating temp should not go below 87c IMO. If it does - monitor when it does it and what impacts it. Normally an idle in traffic will be harder on the car's coolant system than moving along.

When moving at speed you have the extra wind blowing through the rad and engine compartment, a weak stat will show itself as a drop in coolant temperature when the car starts moving (80c or below) I have seen them go as low as 65 - 70c when driving. A sure sign the stat is no longer doing its job.

EVERY Mercedes I have ever bought, bar none, has came with a dud T stat.

They should be considered a service item and renewed at coolant change IMO.

 

[gsxr]

Warm up time should be quick. In any of my m104s or m119s they are fully up to temp after driving only 2 or 3 miles. Aka less than 3 - 5 mins temp is up to 87c. Any longer than that is suspect.

100% correct - assuming the 2-3 miles driven are at decent speed, i.e. not idling through a neighborhood at 20mph. But yes, temp should increase rapidly.

The operating temp should not go below 87c IMO.

This number may vary based on how accurate your dash gauge is, vs actual temps (I like to compare to live data via SDS). However, the FSM indicates that the start of thermostat opening is 78-82°C, and is fully open at 94°C. I've seen some of my cars hang around the 80-82C range in cooler weather, and I don't think this is a cause for concern. See FSM job # 20-0200, click here for PDF file. Note the same document has errors elsewhere... fan cut-in is at 92-100C coolant temp, not air temp. And the fan/engine speeds are backwards (fan spins faster than crank).

When moving at speed you have the extra wind blowing through the rad and engine compartment, a weak stat will show itself as a drop in coolant temperature when the car starts moving (80c or below) I have seen them go as low as 65 - 70c when driving. A sure sign the stat is no longer doing its job.

If I saw anything in the range of 65-70C when driving - that is absolutely cause for concern! I don't think I've ever seen temps drop below ~75C under any conditions when driving (after the engine is fully warmed up, 80C+), with a good t-stat. The t-stat should be fully closed below ~80C. Temps <75°C are generally a classic sign of an old, weak t-stat.

They should be considered a service item and renewed at coolant change IMO.

Definitely a good idea to replace proactively at coolant flush time, or every other coolant flush, depending how often you change anti-freeze.

 

[JC220]

If I saw anything in the range of 65-70C when driving - that is absolutely cause for concern! I don't think I've ever seen temps drop below ~75C under any conditions when driving (after the engine is fully warmed up

These low temps were observed on cars with stuck thermostats Dave. Literaly stuck open when I took it out. Most recently my 140 S320 which ran very cold on the journey home had a stuck open stat. I put a new serpentine belt, rad cap and thermostat in its matter of principle and new coolant. It was running at proper temps then.

I noticed the low temps when the PO came to give me a test drive in the S320. I asked him did he notice it ran so cold - he had never thought about or noticed it! It was a cold drive home too with the heater barely keeping up.

 

[gerryvz]

Thermostats can stick closed as well ... which is what happened with my G-wagen, and caused the amount of coolant that was allowed to flow through the radiator to be very small.

Notes on G320 Radiator Replacement | G-Wagen Models

I replaced the radiator on my 1995 G320 today, using the Nissens unit. The date code on it was W23 2018 (week 23, year 2018). It is the same radiator part number used for most all W463 G-wagens. Behr and Nissens units are available; the Nissens unit is well under one-half of the Behr unit. It...

www.500eboard.co

Length of warmup time (coolant to 87-90C indicated) is a dead giveaway to a faulty thermostat. This is what happened with my 560SEC a couple of years ago. It would take 20 miles to get from 80C to a proper 87-90C. Now it warms up like it should, as does the G320.

HOW-TO: Replacing M117 Coolant Thermostat (5.6-liter motors) | C126 "HOW-TO" Tutorial Articles

Since moving to Maryland in late October, I've noticed that with the cooler temps, it has been taking my 560SEC an extremely long time to reach operating temperature, as indicated on the coolant temperature gauge in the instrument cluster. Even after driving 10-20 miles, the coolant temp gauge...

www.500eboard.co

If I had a car that spent any length of time much below 85C, I'd be replacing that thermostat. The exception to this would be very very cold weather, as in the 20sF range. 80C is too low, as is 105-110C too high. WIll it kill the engine? No. Is it normal? No.

A bad/tired thermostat is like bad/tired motor mounts. They sneak up on you gradually, to the point where you think their behaviour is normal. But it's not, and you have to know/remember what the proper behaviour actually is to diagnose it.

Cheers,
Gerry

 

[northNH]

My recently acquired 420 had all the signs of a lazy thermostat that never indicated above ~85° when idling with AC blowing cold...
(tho’ ambient Tmax=85° here so far this summer, and no real traffic to be found).
Replaced (MBz OEM) with correct Wahler 3 weeks ago; no change, 10min to full temp.
Replaced with another new Wahler yesterday, now behaving AOK.
Both removed thermostats looked fine; did not test either, but the proof is in the temp gauge pudding.

 

[gsxr]

If the bad ones were taking 10 mins to reach operating temp... how quickly is the good one reaching operating temp?

 

[northNH]

4-6 min to thermostat starting to open at ~75°; levels out now at 85-90°...

 

[JC220]

Yes I find a healthy stat will have the motor up to temp quickly.

I have a new late style MB Wahler stat for the green goddess motor. Here's hoping its not a dud

 

[gerryvz]

OK, you guys have inspired me to replace the fan clutch this weekend with the new, factory unit in box that I have stashed. Should be interesting with my bad finger, but having the MB tools should help the process quite a bit.

I'll document the process and add it to the existing "HOW-TO" for those who have obtained factory tools.

 

[gsxr]

I did a bunch of fan clutch testing over the past couple of weeks on different cars & spare clutches. I was able to get the R&R process down to 15 minutes... only possible if all the bolts spin freely, which they generally don't if it's the first time they've been disturbed in a decade or more. At some point I need to shoot a video of the R&R process.

 

[gerryvz]

I did a bunch of fan clutch testing over the past couple of weeks on different cars & spare clutches. I was able to get the R&R process down to 15 minutes... only possible if all the bolts spin freely, which they generally don't if it's the first time they've been disturbed in a decade or more. At some point I need to shoot a video of the R&R process.

The last time I replaced my fan clutch, I was careful not to over-tighten the center bolt. I'm hoping that it will come off rather easily.

 

[Thierry]

...but some of the factory clutches arrive mis-calibrated and don't engage fully until engine temps are high enough to cause most people to wig out.

Currently there isn't a good OOTB solution; except maybe running the OE clutch in winter and aftermarket in summer?

i have the 700 euro new oem clutch and it doesn't work well in city traffic. T° climbs untill electro fan get's in. It's a difficult subject. How about converting to full electric fans?

 

[gsxr]

Jelmer did a full conversion to electric fans years ago, it was documented in detail on an old forum thread. Quite a bit of work though, and it will be louder than the mechanical fan.