Hikingmapa

The E300 TD's radiator temperature has been creeping up. Today, it ran into the red zone with radiator fluid leaking from the cap. It was only ~75F outside with air conditioning running, stop and go traffic. When I checked, the radiator fans were barely turning. I recalled they turned at high speed on a hot day. What connects the fan speed with the radiator fluid temperature? Any idea what gives? Thank you.

Plutoe

This is very strange, there is a resident "I" in another forum who indicates to folks that to solve his diesel overheating problem he removed all the fan blades. Go figure.

One thing for sure is that diesels run cooler than gassers and although you may have a fan clutch problem, I believe there are other things going on within the cooling system to cause your problem, possibly a bad thermostat-----and that is were I would start.

PS: also use the correct fluid, not the pink or green crap!!

Hikingmapa

Hi Plutoe, thanks for the thought. I did have the thermostat change a couple of yrs ago due to it stuck in the OPEN position; it was freezing in the car!
THinking out loud, I guess if the thermostat stuck again half way, there may not be enough heat going thru the sensor? to trigger increase in fan speed?

Plutoe

Freezing makes sense in the winter, with no restrictions in the system how do you get the system up to 80C---very hard. The opposite may be happening---very small opening that allot of hot water needs to pass through to transfer heat-------overheating---not good.

A simple test would be to remove the thermostat and watch the dash gage or and not very scientific, but put your thermostat and thermometer in a pan of water and watch for when it starts to open. Good Luck

Plutoe

Quote When I checked, the radiator fans were barely turning. I recalled they turned at high speed on a hot day. What connects the fan speed with the radiator fluid temperature? Any idea what gives? Thank you.<!-- google_ad_section_end --> Unquote.

Since late 1995 MB aux fans have been controlled differently, depending on year mfg.

As of 1997 our diesels aux fans have been controlled via the SAM and air control module. When the coolant gets to 103C and or the refrigerant pressure exceeds 13 bar the fan comes on and when those values drop to 100C and 12bar the aux fan is turned off. It is either on or off. simple as that. Hope that adds to your understanding. Good Luck

Hikingmapa

Its been a year, and after a blown radiator, I have a new radiator. Temperature is still high ~110C and the aux fans still did not kick into high speed. A shop suggested to check for AC refrigerant leak. They somehow think low in refrigerant will cause overheating. They also checked the resistor network that they said control the fans, and that is ok. I am tempted though to change the temperature sensors because that seems to be the logical thing to do. Plutoe, you mentioned SAM and air control module. What is SAM stands for and where are they located? I did change the air blower motor regulator. Will that be the problem?

toby1

90ºC sounds fine for one of these.

Mine runs at 88-90ºC and that's perfectly normal operating temperature.

Hikingmapa

My mistake. It runs ~110C city driving (I did go back and edited the post on 7/16.) On freeway, it does maintain temperature ~80C, which is around the temperature it used to run before the problem.

nelbur

If it cools well on the freeway, you may have a problem with the clutch on your mechanical fan. It should not free wheel when the engine is hot. Your electric fan should come on high when the temperature goes up, but I don't know where the sensor is on your car. I would have someone check both the fan clutch and the temperature sensor for the electric fan.