Engine runs hot only when AC is on?
 

I have noticed that my 1987 300D has been running hot when the AC is on. The AC system works great. The engine runs around 85-90 when moving but if i am in traffic the temp creeps up to 100, which is when i turn the AC off and the temp then returns to normal. any thoughts?

Thanks,

G

Electric fans working properly?

they seem to come on but I am not sure what the exact operating protocols are for them.

AC puts extra load on the motor and is making the condenser warm. That part is totally normal.

Most Mercedes high speed fan switches are 105*C. Have you let it go just past 100* to see if the fans kick on? My cars get over 100* with the AC on and at 105* the high speed fan comes on the temp holds and then drops down a bit in traffic.

When you start moving the temp should drop back down in between 80 and 100.

I have not let it go over 100*F. does the fan change speeds? if so will it be visually obvious when the fan goes in to high speed? or is this just that the fan will turn on at 105*F?

I can't remember on the 87 if the big single fan is dual speed.

The 2.5 cars used two E-fans, a high and a low speed.

Also, your mechanical fan clutch could be getting weak.

there are two fans on inside and one outside of the radiator/cooler. I'll take a look later this week when it stops raining and gets hot again.

thanks

Insufficient cooling
 

If so, your car has been modified. The stock 1987 300D Turbo comes with one mechanical fan, engine driven, with clutch, and one electric fan. The electric fan has a "low" speed triggered by high pressure in the refrigerant line and "high" speed triggered by a thermal switch in the engine's water jacket (the resistor that puts the fan in "low" speed is on the left side of the engine bay, just behind the headlight assembly). Depending on which switch is in the water jacket, the electric fan will run in high speed beginning at 105C to 125C.

Jeremy