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.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

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?)

__________________
________________________
2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro

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!

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

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.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record