spida

Hi there,

im continually having a problem with my car overheating... i.e. hitting 120C and above!!!!!

i dont think my aux fan is kicking in, how can i make it run even at a cold temp??

MB AMG

Stop the car if the temp get's high and wait until you hear a click and a fan spinning. I don't know all the technical details. Oh and BTW, that fan makes a hideous noise when you rev the engine!

spida

the fan doesn't spin at all... ever
maybe a job for an electrican

JoeR

Uhhh, is this problem on your Chevy?

It would help to say what year / model it is.

Anyway, likely problem is the temp switch that kicks the aux fan on when hot.

overboostTSI

I had the same problem on my 1990 300e. THe problem was both fan motors were broken. I don't know what caused it(maybe Chicago winters).

One way to test the fans is to disconnect the thermal switch and see/hear if the front fans kick on. Also check (with the engine cooled down) to see if the fans spin freely.

spida

sorry, its a 300E 1987.....

i dont know where the thermal is...

JoeR

Ahhh, '87 300E... I can help now, since I just recently solved overheating problems on mine.

The thermal switch is on the air filter side of the head near the center of the engine next to the valve cover. There will be 3 wires. The two vertical sleeved posts are to the switch. Just jump them (to bypass the switch) with the engine running and the aux fax should run. That will tell you if it's the switch. If not you need to troubleshoot further (likely fan motor or wiring). My switch was bad. Cheap and easy to replace.

Also my viscous clutch was shot. With a cold engine there should be considerable resistance to turning with the engine off. It should couple on startup (it'll be louder) then loosen after startup. Look for oil leakage there. If the seal goes, so goes the fluid and it won't work right. If it's sitting idling where the engine starts getting hot you should also hear it couple. On mine I (very carefully!!) inserted a stick with it running and engine hot and was easily able to stop it. That showed it was bad.

After replacing the switch and clutch it stays cool now.

Also you should check the bearing behind the clutch & fan. It is known not to last long.

Good luck!

Jer

You do not jump the switch to engage the fan. Just remove the plug from the switch, and the fan should run.

spida

Great help guys.... very thorough..

im going to check it out now... thanks for your help

bamberger_1

If you talking about a 300E with A/C there are two things to keep apart. The fan in front of the radiatior is linked to the A/C system and cools the condensor of the A/C, which is the "radiator" you find in the front, behind this one the "real" radiator for the engine cooling is to be found. The engine cooling is managed by the liquid coupled fan in front of the engine block. If the fluid coupling is shot the fan never reaches full speed. When the car is hot and the engine OFF, you should not be able to spin the fan by hand more than 90 degrees. The fan(s) in the front of the radiator shall come on when the A/C fluid pressure exeeds certain levels. To test you need to jump the pressure switch wire on the top of the dryer bottle. Turn key in ignition (engine not running) pull the wires from the top of the dryer bottle and connect them, and the fan(s) shall operate. If not find the plug for the fan(s) somewhere under the dryer bottle, pull the plug and apply 12V if the fan(s) dont run there are shot. No repair possible just replacement.

JoeR

The electric fan is a two speed and had two controls to activate.

1. The water temp switch on the head that I previously mentioned will activate the fan on high speed when water temp hits approximately 107 deg. C.

2. When A/C pressure hits 16 bar the fan will activate on low speed.

This is per the factory CD specs, not an opinion.

bamberger_1

JoeR, your are right, but I dont know excactly the year MB switched to a "two fan in parallel design" which only are activated by the pressure switch on top of the dryer. It is in the 90' models, but as I said dont when it started.

BamaMB

My 1990 300E has the two aux fans.. Having some trouble with them. In the past (and I'm just basing this on memory) the left side fan came on when ever the A/C was turned on and the right fan would cycle on and off. I guess the right fan is controled by the head temp switch. One question I have, where are the relay(s) for these fans located?

bamberger_1

As far as I know there are no relays-. The fans are switched directly by the pressure switch. I had the fans out in my '90 W124 260E and they both were just of parallel operation and controlled by the pressure switch on top of the dryer bottle. I fyou take out the front fan cover you can follow the wires to find out.

Jer

I believe there is a relay for the aux fan, located in the fuse/relay box. The temp sensor on the head is also used by the climate control.