Optimum Coolant Temp.
 

What is the optimum coolant temp. for 1988 230ce(4cyl).And when the engine fan should spin at highest speed??
My car runs between 70-80c on highway,and it reachs to 90c only in traffic and at 90c the engine fan starts and the temp goes back to 80c.

For emissions that engine is designed to run at 90C-100C.
The best temp is around 80C.

What about for a M104 engine ?

I heard 90C is the best for thermal efficiency.

Neil

My m104 seems to like right around 80, maybe a little more in traffic, up hills, with a/c, etc. Usually NOT up to 90.

I am curious what the optimum is. Should you start worrying if the car reads, oh 100 or 110 and holds there, considering the red zone is 120? (Barring the obvious fact that is usually doesn't read there so why is it now?)

In the years I've owned my W124, a tad under 85C seemed to be the nominal operating temp. I only saw 90C and above on VERY hot days, during which the car is sitting in traffic for extended periods...at which time, the fans kicked on and took care of that quickly.

Whenever I saw temps of 90+ during normal driving, it was usually a signal of impending cooling system component doom...and 100% of the time, it was!

Thermostat ratings specify that a new thermostat starts to open at 87 C and is fully open at 102 C. Mine runs in the 85C-90C on the open road and 90C-98C in traffic.