300D overheating
 

My 1992 300D has run hot since I moved to Arizona. I've replaced the radiator, thermostat, cleaned the A/C condensor and have a 50/50 mix with wetter water. When I run uphill on I-17 at 75 mph the temperture goes straignt to 115-120C. Turning off the air conditioner keeps the temp from going to 120. Is this normal? I've been reading on this site about "citric flush" which my local mechanic has never recommended. Any ideas??

What about your electric auxiliary fan, or belt driven fan clutch?

The aux fan should come on at or around 105c, if not, check the temp sensor, they do go bad!

one idea.... you could sell it to me cheap. then, i'll let you know how it runs in nuevo mexico. LOL.
another idea, have you blown the radiator and condenser out with air? get all the bugs and and dirt out you can. don't use water, it will just make mud.
check your thermostat to see if it's opening all it should.

where is the temp sensor for the electric fan located???

The aux fan temp sensor is located forward top of engine, very near to the upper radiator hose. Should be 2 sensors there, one with 2 pins, the other with 3 pins. I believe the one were talking about is the 2 pin.

Ideas
 

Here are some possible causes for your problem.

Aux. Fan Resistor
Auxiliary Fan Assembly
Engine Temp. Sensor
Fan Clutch...
Water Pump
A/C ACC Temp Sensor
A/C Temp. Switch

This requires a high percentage of the total engine horsepower, which will put a significant percentage of total heat into the radiator.

75mph produces a lot of 'ram air' effect, so I don't think the auxiliary fan adds much to the airflow. Ditto the engine-driven fan. The cooling is determined by the radiator effective area and the water pump flow rate.

Ambient temperature has an effect, too! :D

It sounds like it is not overheating, it is just running at the hot end of allowable. Given high ambient temperature and high horsepower requirements, it is to be expected.

By the way, what does the temperature gauge read when you are going downhill? It should drop back to 80-85C...

Best Regards,
Jim

300D overheating
 

Thanks for the help. The temp drops bak to 80C when the car goes downhill. Temperature is a factor, but the car will get hot going up hill in cool weather without the A/C. My local mechanic--very good--says this high temperature is normal. I'm wondering if I need to flush. Everything else has been replaced or checked.

It sounds normal, especially since you have replaced the 'usual suspects' of thermostat and radiator.

I think you can trust your mechanic. Watch it for a while. A flush won't hurt, but it may not help, either...

Best Regards,
Jim

Does Auxiliary Water Pump useful for reducing overheat?
Can I replace the expansion plastic tank with a bigger one on my 300E86? What is compatible?

only thing
 

left is the water pump. i would prob change that. be sure to get the origninl style with the cast impeller blades.

tom w