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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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Discussion Starter #1 (Edited)
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 the cooler engine temp is the better 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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1994 E320 Wagon,1999 E320 Wagon,2000 E 320 Wagon, MGB Track/Rally, ,1988 300E ,more....
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You have the m104 engine,not noted for as high mpg

like the m112.Thermostat set for 87c typically runs at about 80c in the cooler months about 90c in the summer.
No harm changing it,I just don't think you will see much of an improvement.Up your tire pressure to 32 front and 38 rear.Are you running non oe wheels like 18's they will kill mpg.Clean you mass air sensor.Have you changed your o2 sensors?Clean air filter from autohausaz.com.
good luck
 

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1922 Ford T no OBD, no ECU, no SCN
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Before replacing thermostat I would check the temperatures with infra-red thermometer.
I did the trick with my Ford Powerstroke. Some company makes big money selling 185F thermostats to replace the 170 stock (from what I remember). On my check the new thermostat opens at 175F, what is only 5 degrees higher, than the OEM. The salesman told me this is how it suppose to be. Without the thermometer I would feel the power gain for sure.
 

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1997 E320, 1997 S320
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good job texholdem, nice work.
yeah, that doesn't seem excellent gas mileage for combined city/highway. thermostat could be the problem. also you could be due for a tune up? i have the m104 in my e320 and i get 18mpg all city driving, and if it's mix city/highway i usually get above 20mpg, and if it;s all highway usually it is 27-28mpg. on my s320 which is a lot heavier than the e320 i get about 16-17mpg city, and they both have the same engine. also gas is different from state to state, so that could be part of it too.
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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814 Posts
Discussion Starter #5 (Edited)
like the m112.Thermostat set for 87c typically runs at about 80c in the cooler months about 90c in the summer.
No harm changing it,I just don't think you will see much of an improvement.Up your tire pressure to 32 front and 38 rear.Are you running non oe wheels like 18's they will kill mpg.Clean you mass air sensor.Have you changed your o2 sensors?Clean air filter from autohausaz.com.
good luck
The tank flap says for tire pressure 29 front and 32 rear, is it OK to raise to 32 front and 38 rear?

I have stock tires 215/55/16, gonna change air filter today.
In the case of no improvement, I'll consider the O2 sensor as next.

Thanks!
 

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That

is fine for good tires.If ride is to firm set them at 32 front and 36 rear.The best investment to proper tire inflation is a good gauge not one of those cheap pencil ones but a good 20 buck quality one.
A lazy o2 sensor will really affect mpg and they are 80-100k mile maint items.
Have you ran a can of seafoam injector through a tank of fuel?Dirty injectors kill mpg.
:bowdown:eek:hlord
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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Discussion Starter #7
I got a Techron bottle, will use it next time tanking. Is seafoam better and is it available at autoparts resale or only on-line?
 

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Techron

is good stuff also:thumbsup:
seafoam at autozone,napa etc.
With that engines higher rpm power curve a lot of members have found a few mpg by avoiding jack rabbit starts,ease away from the lights and gradually work the car into its power band.
:bowdown:
 

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2001 SLK 320(217K Miles), 2002 E320 Special Edition(183K Miles)
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With 38 at the rear, you are bound to get some center thread wear. Frequent back to front rotation should take care of it.
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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Discussion Starter #11
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.

Someone pointed out to me that the old thermostat was definitely bad, it appears in the picture open, so I'm adding another pic to see it more clearly. The gasket sat very tightly, I had to pry it out with a hook, it looks a bit torn.


 

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Spot on

you are perfect now on a 60f day in the big D.Now get the techron or seafoam in and see if you can get those mpg's up.:thumbsup:
:bowdown:
 

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2004 CLK 240 Coupe
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You should be able to watch the thermostat open if you place it in a saucepan of water and heat it up on your stove. If you also have a thermometer, you can note the precise temperature when it moves.
 

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W210 1996 E320 Smoke Silver. [W124 1990 300CE Artic White - Sold].
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Discussion Starter #14
You should be able to watch the thermostat open if you place it in a saucepan on your stove. If you also have a thermometer, you can note the precise temperature when it moves.
The bad one stays open all the time, and the new one is already installed. Next time then, thanks! :)
 

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Discussion Starter #15
you are perfect now on a 60f day in the big D.Now get the techron or seafoam in and see if you can get those mpg's up.:thumbsup:
:bowdown:
Thanks ohlord, I'm gonna take the measurements one after another, to see which one really kicks in. If I did them all at the same time I would not know.

1. Thermostat
2. Techron
3. Higher tire pressure
 

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can we add to DIY section?
Where you been? It's in there.

Nice job, texholdem. Now you're immortal. :)

Good luck with chasing the mileage gremlins.

And based on the fact that your old one was stuck open, I'd bet you'll see a decent mileage improvement. Particularly if you're in a colder climate, then engine would take a long, long time to get to operating temperature, and if you were driving moderate roadway to low freeway speeds it would probably never really get to the proper temp. Surprised this didn't reflect on the dash gauge.

Take care and enjoy the ride,
Greg
 

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Discussion Starter #19
Where you been? It's in there.

Nice job, texholdem. Now you're immortal. :)

Good luck with chasing the mileage gremlins.

And based on the fact that your old one was stuck open, I'd bet you'll see a decent mileage improvement. Particularly if you're in a colder climate, then engine would take a long, long time to get to operating temperature, and if you were driving moderate roadway to low freeway speeds it would probably never really get to the proper temp. Surprised this didn't reflect on the dash gauge.
Take care and enjoy the ride,
Greg
It did, as I said I got just about 70C even after 20, 15 miles driving, the whole time before the replacement.

Thanks for adding it to the DIY section :)
 

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I have an 2002 Acura MDX, it is notorious for its transmission. It had a recall on the transmission and Acura had to add a "fluid jet" to cool some internal part down. My MDX's transmission was declared "transmission failure" by Acura dealership and it was replaced under warranty. (There were many MDX owners had their transmissions replaced under warranty.)

After the transmission was replaced, a side effect was that I gained 1 mpg (according to the built-in computer), from 15.8 mpg to 16.8 mpg (city and freeway combined).

I'm not suggesting that you have a transmission problem for your not-so-good mpg on your MB; certainly not recommending you to replace your transmission. :) I only thought that it's interesting to mention it.
 
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