Lower-temp thermostat for M119?

[Ab150]

Hi all

Apologies if this has been covered before. Am writing to see what temperature thermostat you all use in your 500E/E500. I have 75 degree thermostats in my 6.3 and 250C, which keeps the temps right around 175 degrees. I believe my E500 came with a 87 degree thermostat which is higher than I would like. Does anyone run a 75 or 80 degree thermostat? I am also installing a new radiator and fan clutch, plus all hoses, so I might as well change the thermostat. Car runs between 90-100 which is hotter than I would like.

Thanks, as always.

Andrew

 

[gerryvz]

Earlier MB engines such as the M110, M130, and M100 were designed to run with different (cooler) operating/cooling temperatures than later engines such as the M117 and M119, and thus used thermostats that were "cooler" by design.

This cooler thermostat/cooler running design included the earlier, iron-block versions of the M116 and M117 engines (3.5 and 4.5-liter displacement).

I mentioned a cooler running (71C) version of the thermostat that is designed to be used in the alloy-block M117 and the M119, in this post. It is readily available in the US through various vendors.

My recommendation is to use the original-spec version of the thermostat for your car. This is based on geography and expected running conditions for the vehicle, and the "stock" operating temp is programmed into the computers of cars that have them (perhaps not applicable to pre-computer cars).

In short, I would be very very careful about running a cooler-than-stock thermostat in a car that wasn't expressly designed for it. For M119 cars, which do have both ignition and injection computers, this is especially true. I would consult an expert like our member Klink to help with the decision to do this or not.

Cheers,
Gerry

 

[Klink]

I like running the thermostat that the engineers specified for the car in question. A fine point that is very often missed when people are discussing thermostats between different engines, thermostats that often differ by 5 to 10° C is that when used in their correct applications, these almost all result in fairly similar operating temperatures. A common enough example exists with the M110, though there are numerous others. It is well known that the M110 thermostat which is also used in a number of other engines has an 87°C “start of opening“ temperature. Note that this thermostat is in the hot outlet area of the system, the area from where hot coolant flows TO the radiator. People have pointed out that in comparison, some diesels of the same vintage run an 80° thermostat of very similar construction. What they fail to notice is that on those diesels, this 80° thermostat is in the water inlet area. They are in the area where cold water flows from the radiator to the engine. This is one example of at least four that I know of where people compare "apples to oranges" when discussing the relative merits of either temperature. Do note that all M119 engines that I know of, and that’s probably all of them, have a thermostat that is in the cool water inlet portion of the system.

Do note the location of the thermostats whenever you are thinking about relative temperatures, etc.

Overall, the people that designed your car knew at what temperature relative to ambient they wanted the engine to run. They chose the cooling system components accordingly. Interestingly enough, manipulating thermostat temperature on newer engines often leads to comical results. Most of the engine management going into production from about 98 on have temperature versus time and load comparison maps and they will fault code for too cool of a thermostat, or a thermostat that has been “modified“ Lots of check engine light fault codes for a number of years now have been caused by lazy, broken and/or leaking thermostats.
Emissions, fuel-efficiency and even to some degree engine life all really hate a slow warm up period. A number of models for years now have had thermostats regulated by the engine management system.

Imagine a conventional wax thermostat with a say, 115 degree C start of opening temperature. Put a heating wire into the expanding wax portion, and there you go. They dummy up the instruments so the customers don't freak. Here's an approximation of what actually happpens: When the management is keeping the engine at a hot and scary emission and efficiency enhancing 115 when idling in traffic, the gauge shows a nice confidence building 88. When it is lowering the temp to 72 during a low load high speed cruise for lower NOX emissions, the gauge shows a nice stable 84. The gauge goes to undamped live when a malfunction or implausibility is detected, along with a warning of cooling system defect, and/or a check engine light. Truth is, they could probably completely dispense with the coolant temperature gage, as it is still mostly there just to satisfy tradition, just as oil pressure gauges were for a good decade or three after which they no longer served any genuine purpose.

DON'T remove that pressure cap from a newer car sitting there at hot idle showing 85 on the gauge! You are about to spray REALLY hot coolant all over the place, including possibly your face...

 

[Ab150]

Thanks, guys - interesting information. I think the primary unnerving factor to me is the variability in the engine temperature - my other Mercedes (6.3, 250C, 300D-Turbo) all run around the same temperature unless it is really hot outside or in prolonged traffic, whereas the E500 varies quite a bit highway vs city, regardless of ambient temp. Hopefully a flush and fan clutch (fan clutch not engaging correctly) will help that.

Andrew

 

[samiam44]

Andrew,


I've found on my car- the temp is very stable *IF* I am utilizing the climate control system(aka w/ the a/c on). The a/c system has a high pressure switch which kicks in during low speeds to keep the freon pressure down to a reasonable level which also keeps it cooling. That has a net effect of keeping the car running 90 c. For me, that seems rock-solid till I get above 100-105 F outside. This last year, I had to replace that pressure switch- oil consumption dropped and the temp went from bumping 95-105c, back down to the normal 85-90c.


Sincerely,

Michael

 

[Jlaa]

Putting this info here for posterity. I could not reference this old post about a 71C thermostat for the M119:

I mentioned a cooler running (71C) version of the thermostat that is designed to be used in the alloy-block M117 and the M119, in this post. It is readily available in the US through various vendors.

My recommendation is to use the original-spec version of the thermostat for your car. This is based on geography and expected running conditions for the vehicle, and the "stock" operating temp is programmed into the computers of cars that have them (perhaps not applicable to pre-computer cars).

And then from here: High Temperature Issue While Driving | M119 Engine I found reference to this:

I believe for many MB thermostats there were versions available that allowed the vehicle to run cooler. There definitely is for the M104 (I've seen the "cooler" version in MB literature) and I seem also to remember a cooler-running version for the late M117/M119 as well.

However, these cooler-running versions are designed for extreme environments (for example, if running in desert-type environments) and not for regular/ordinary motoring conditions.

In my opinion, they should never be used unless conditions warrant.

I will have to do some digging to find these cooler thermostat part numbers for the M117/M119 and M104 (they are different models of thermostat).



Behr made the part, 116 200 02 15 75, and I believe it was a 71C thermostat. It is permanently NLA.
EDIT -- this is for the early M116 and M117 engines, not the 5.6-liter later M117s, which share the same thermostat with most all M119s as found in the E500E.

Will keep digging......

And I think I found the thermostat from the "RBE Marius" videos. Everyone hates on the voice in these videos but I find them entertaining. FWIW the RBE Marius video says "Made in Poland" but the Mahle TX 26 71D1 is clearly marked in the video as made in Germany. Also I don't think a lower temp thermostat will solve an issue where the car is unable to keep up w max cooling demands --- but again I am putting this here for posterity.

This thermostat is available at an attractive price point:



And various online application catalogs claim it is suitable for an M119 (who knows really - below from eeuroparts.com)



RBE Marius Video Link on ZuckBook
Screen cap here:



Also video attached below. The first version (zzzz) uses H265 and I was able to view using VLC but not Quicktime. The second version (aaa) is lower quality, using H264, and I could view it using both VLC and Quicktime

 

[gsxr]

If start of opening is reduced from 80 to 71... the next question is, what is the temp of full opening? If it's the same, there's zero benefit to the lower-temp t-stat. If the 71C unit has ~9° lower full-open temp that might be interesting for high ambient temp locations.

 

[Jlaa]

If start of opening is reduced from 80 to 71... the next question is, what is the temp of full opening? If it's the same, there's zero benefit to the lower-temp t-stat. If the 71C unit has ~9° lower full-open temp that might be interesting for high ambient temp locations.

This is what I found. When does the stock 80C thermostat go fully open?

 

[gsxr]

FSM says max open at 94°C, although for the StovetopTest® you may need to compare with a stock t-stat.

Also not sure how well the IR gun reads through liquid? Any chance you have a probe-type thermometer? However, the opening measurement is close to spec, and total range (~9°C) is not too far off the ~12°C range from a stocker.

 

[Jlaa]

Also not sure how well the IR gun reads through liquid? Any chance you have a probe-type thermometer? However, the opening measurement is close to spec, and total range (~9°C) is not too far off the ~12°C range from a stocker.

Yeah! I had a probe and was running it in parallel with the IR gun and it was about the same reading…. But too difficult to photograph!

 

[doolar]

Putting this info here for posterity. I could not reference this old post about a 71C thermostat for the M119:



And then from here: High Temperature Issue While Driving | M119 Engine I found reference to this:


And I think I found the thermostat from the "RBE Marius" videos. Everyone hates on the voice in these videos but I find them entertaining. FWIW the RBE Marius video says "Made in Poland" but the Mahle TX 26 71D1 is clearly marked in the video as made in Germany. Also I don't think a lower temp thermostat will solve an issue where the car is unable to keep up w max cooling demands --- but again I am putting this here for posterity.

This thermostat is available at an attractive price point:

View attachment 199296

And various online application catalogs claim it is suitable for an M119 (who knows really - below from eeuroparts.com)

View attachment 199297

RBE Marius Video Link on ZuckBook
Screen cap here:

View attachment 199293

Also video attached below. The first version (zzzz) uses H265 and I was able to view using VLC but not Quicktime. The second version (aaa) is lower quality, using H264, and I could view it using both VLC and Quicktime

Omg what’s up with the sound on these?