I decided to replace the thermostat because I am having bad fuel mileage (17-18 mix 65% highway 35% city) and my engine temperature won't go over 80C and I read somewhere that a bad thermostat may be the cause.
(Before that I thought cooler engine temp is good for the engine).

The job is simple for DIY rookie like me, just remove 3 10mm screws (# 1,2,3 on the pic) on the housing cover using a rachet with a long extension. That should be done on a cold engine.
Unflug connector #4 else the cable will be in the way when removing the housing cover.

The cover and the old thermostat may sit tight perhaps because of the gasket sticking tightly, just use a little force. The spillage is minimal, about a cup of coolant.
Remove the thermostat and put the new one together with a new gasket in.
Attach the cover, start the engine and check for leak.
1: new thermostat
2: base of housing
3: housing cover, displaced
4: old (bad?) thermostat.

hoping for some mileage improvement.

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE

This DIY is now in the Wiki HERE.

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Bill Wood - Retired Webmaster
My Personal Website
1998 Mercedes E430
2010 Toyota Sequoia
My Photo Albums

Are the referenced photo's stored somewhere. I do not see links for em.

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Brian G.

1994 E320 Wagon with many warts SOLD
1995 E320 Wagon with a beauty mark or two FOR SALE

Your old thermostat is definitely bad. It appears open in the picture.

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1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

cjlipps, Thanks for pointing it out to me. I guessed it was bad but was not sure. After the replacement the engine temperature climbs to 87C just after 2 miles, which is supposed to be, right? It remains at 87C all the time except for stop-and-go traffic, which is about 90-95C.

I am adding another pic of the bad thermostat, the gasket was torn a little bit because I had to pry it out with a hook.



BMG, can you see the pix now? perhaps after refreshing your browser?

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

---------------------------------------------------------
1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE

I am on my home computer and can see them clearly. IT probably has things locked down tight on my laptop.

Nice DIY tutorial

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Brian G.

1994 E320 Wagon with many warts SOLD
1995 E320 Wagon with a beauty mark or two FOR SALE

Thanks for the DIY write up and photos.

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2010 W212 E350 Sport
1996 W210 E320 (220K miles)

Very straight forward.

> (Before that I thought cooler engine temp is good for the engine).

Why is it not good?

I have ml320 and it runs 81 on freeway but on stops it climbs to 95.
Last year i noticed it when i had a crankshaft sensor go bad in the summer. Normally after engine temperature went over 81 it would stall. Thanks to this forum i fixed it but started to pay attention to engine temp. I flashed the system, using citric acid and mersedes degreeser, refilled with g5 antifreeze but still no luck. I think back in the day when i first got it, it never went over 81.

Now the summer is comming and im thinking about removing the thermostat completely!.

Btw, I put in new wiscose fan cluch too ($185 for the part) with no difference.

So why do u think cooler engine is bad?
Also, can anybody confirm that 95F is normal for ML?

Thanks

95 is a good bit higher than a ML should be. It should just be over 80 in the 85-87 range. The thermostat on your engine is different, It's built into the upper hose fitting, i.e. if you remove it, there's nothing for the hose to attach to

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

All these temp ranges are within spec. 80c is 180 F and 100 c is 212 F. I know it will vary from car to car............

Yes, i saw it on the picture, its an assembly. I guess i will put a new thermostat in (I have 175000 miles on the car). Its $25 bucks from ***************.
But first i will try to take the guts out of the old assembly and put it back, making it to just free flow. That way i will at least test for general cooling efficiency of the system. If it stays below say 80 all the time that would mean that i dont have other problems (like clogged radiator or block, improperly dilluded antifreeze, improper belt tension, water pump, fan cluch or whatever else may go wrong there).

So can anybody tell me why it may be bad to run cooler engine?
I will put it back together for the winter...

Oh, and did anybody ever found a drain plug on the block on MLs? I couldnt find one last year...

Thanks

the engine control computer, wihich reads coolant temperature, will run the engine richer until it warms up and therefore a "cool" thermostat could lead to poorer gas mileage. Then again, I could be wrong.

I have found this thread on gardenweb http://ths.gardenweb.com/forums/load/cars/msg092255574892.html
they talk a little bit about it.


Here is a couple to the point:

• Posted by ericwi (My Page) on Sat, Sep 30, 06 at 10:25

"One of the products of combustion is water vapor, and some water vapor gets past the piston rings and into the motor oil, in the normal course of events. When a vehicle is started up and driven for an hour or more, the oil heats up, and the water evaporates. By installing a 180 degree thermostat, you have caused the engine to run cooler, and this will result in more water accumulating in your oil, if you do mainly short trips. If you ordinarily drive the vehicle for an hour or more, per trip, then there will be time for the water to evaporate, so there will be no problem."

• Posted by jemdandy (My Page) on Thu, Oct 5, 06 at 3:45

"Raising the coolant temperature from 180 F to 195 F reduces emissios and inceases engine efficiency. However, I suspect that lubricity is better at 180 F with longer engine life. There is an argument that engine life may not be extended since the higher temperature tends to keep more moisture and condensates out of the oil.
The engine may not pass emissions tests when the coolant is too low. Regarding the oxygen sensor, most systems go into "closed loop" operation around coolant temp of 140 F, therefore, the oxygen sensor function should be operable at 180 F. Some systems may set a trouble code for "temperature too low". Some emission test stations scans the engine controller for certain trouble codes."

hi,
just wondering, im from asia and i read many threads mostly about temperature and i feel so confuse...
the gauge temp shows in USA 90-100C is normal?
because in asia, actually im from indonesia for my w124 m104 the temp always stay on 80-85C

is there any different parts between nation?

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