M104 versus M103: Operating temperature.

[sanchezc]

The temperature on my 300SE/M103 stabilizes around 80C, whereas the temperature on my E320/M104 stabilizes around 90C: is this by design, i.e. the case for everyone else here?

BTW sincere thanks to all who contributed to my previous "M103: ..." and "M104: ..." posts yesterday: very helpful. And keep your experiences coming!

This site is so enlightening, hats off (again) to its creators, maintainers and contributors.

[anthonyb]

The M103 is running cold. It should run around 87-90.

[Educaid]

I have a 1989 260E with the 103 engine and a 1993 300E with the 104 engine. Both run the same temperature; about 80 - 85 degrees.

[suginami]

My 1993 300E (3.2) with the M104 engine, ran consistently between 87-90, which is exactly the temp range the engines were designed to run at.

Any lower than that is not normal.

[Ali Al-Chalabi]

Thermostat on both engines is the same temp. Starts to open at 87C and fully open at 102C by design.

[simmo300e]

its a popular mod - at least in this part of the tropics - to replace the thermostat with one that opens at a lower temperature. Don't ask me why, this is what I'm told at my parts shop.

Anyway, this is fine with an older cooling system with a partially blocked radiator as the engine temp stays in spec. However, if you change out your radiator for a new one and replace the visco fan, as I did, the effect is that your engine never actually reaches operating spec and consequently runs rich all the time. Mine sat at just below the 80 deg mark whereas it used to be pegged exactly at 9-o-clock before the rad change.

Took me a while to figure it out but replacing the thermostat with the correct part sorted the mixture out.

[Ali Al-Chalabi]

Yes, always use the correct thermostat. Do not install a cooler thermostat in an attempt to make the engine run cooler. All it will do is regulate the bottom operating range of the engine to be cooler, but will obviously have no effect of the upper range of the engine.

[sanchezc]

So it seems that both the M103 and M104 should stabilize at around 90C. Is that the case for both the E (e.g. W124) and the S (e.g. W126) bodies? Asking because the additional space under the S's hood may result in a lower operating temperature? And if not, what are the consequences / drawbacks of an engine operating at a lower temperature than designed? But 10C lower may not be a big deal...

[anthonyb]

There shouldn't be a difference, regardless of the chassis. If the engine runs consistently cold, it will never leave the warm-up enrichment cycle, which adds gas to the mixture to help get the engine up to operating temperature. Even running a few degrees cold will be less efficient than running it at the standard operating temperature.