M119 running too cool?!
 

I know, I know sounds impossible right? Most M119 owners would love this condition, right? :D

Well, with some recent trips in the E420, (Mixed freeway and around-town driving), I've noticed it never gets much above about 60C! (except for some periods when during extened idling it's crept to just under 80C on the coolant temp guage) Now, I could understand at freeway speeds, the airflow, accompanied with moderate ambient air temps (40-55F), it could concievable stay at or slight under the 80C mark on the temp gauge, but this seemed a little too low to me. I have been using 'EC' mode for the ACC since AC cooling isn't needed, but didn't think this alone would lower temps so much.

Anyone know what optimum operating temp is for the M119 in a W124? I seemed to have had the same, 'running nearly-too-hot' scenario like other 400E/500E owners since I've own the car (last February), so I'm curious as to this recent drop. No cool-harness installed :)

Should I just take it easy, or is this indicative of thermostat/cooling system issues?

Thanks all in advance!


Regards,
- Ryan

M119's run hot in a W124, usually around 100 degrees Celcius and higher.

I'm willing to bet your thermostat is stuck in the open position.

Mine runs a little cool this time of year as well. Perhaps because of the water wetter and the cool ambient temps?

I know, lets race between Seattle and Greenwater and see who's m119 stays cooler???

Ambient temps in Omaha have been between 30-50 F and mine NEVER runs below 80 (i.e., thermostat opening temp). According to Stu Ritter, the quickest way to destroy an engine is to run too col, since the EFI will tend to make it run rich and then there is the risk of excess gas washing down the cylinder walls.

You either have a bad thermostat or a problem in the temperature sender or gauge, I'd say.

Mine always seems to run at the 80C also. It hot weather with the air on it will creep above that , but Like you I am now using just the EC button and 80C or just a little above that is the norm for me

Ryan, Mercedes states that the . . .
 

M119 engine run at 80C or above to meet all specifications.

You have a lot of suggestions for the other members, so I'd look into them asap. Running at 60C (if it really is!) will probably ruin the engine.

If you can get a laser 'thermometer', that an easy way to see what the engine/radiator temp REALLY is! Probably find that it's at least 80C and the temp gauge or sensor has gone bad.

Thanks for the input guys! I'm keepin her parked till Monday when I'm having the t-stat replaced (or at least investigated further). Time for a coolant flush as well before winter anyway. My indie echoed the t-stat suggestion as well. Again, the forum's proved to be an invaluable sounding board of experienced owners!

After that, I'd be happy to take you up on that race Tracy! :) Oh and after the snowshoes (Nokian NRW's) get put on too.

Regards,
- Ryan

After reading the comments above, I will have Stella's Tstat checked as well -- don't want him to get a cold!

BOTTOM LINE - The thermostat should regulate the temp to at least operating temp.

I used to have the same problem...

It turned out to be the temp sender (the blue sensor) which is located below the cover right in front of the airbox.

I figured it was impossible for the engine to be operating at 60 the whole day in 40C degree weather...

I also had the same problem on a 93 400E. In my case is was the thermostat. Prior to replacement is ran 40-60C after replacement it runs 85-90C.

It was very easy to change the t-stat on my car. As I recall it took about 10 minutes - the thermostat is right on top of the engine in the front.

Tim

Well, in my case it turned out to be the t-stat. It was replaced, along with a coolant flush and now she gets right up to 85-90C, and sticks there until you idle for awhile where it will creep into that famliar 100C territory :)

Thanks all for the input!

Regards,
- Ryan

Sounds like healthy M119 behavior! Glad it worked out.