1985 300cd - PeachParts Mercedes-Benz Forum

zman · #1 07-04-2006, 09:59 AM

Hi, I'm new to Mercedes Benz, my youngest daughter bought a 1985 300cd. We drove it home in the fall of last year, about 40 miles, and it ran fine. Drove it this summer and it seems to run a little warm. Took it yo have tires put on it on a 95 degree day and it overheated. The electric fan never came on. The A/C needs recharged so that fan circuit won't help. I do not know which sensor is the fan switch. There are 2 sensors near the thermostat housing and 2 on the left side of the cylinder head. Can anyone tell me which one is for the electric fan?

stcbenz83 · #2 07-04-2006, 10:26 AM

if your not running the AC that auxilury fan should not be running at least to my understanding. I dont have one in mine

the previous owner ripped the ac components out, but mine still runs well below operating temps, maybe you need a new thermostate, or even to modify it.

http://dieselgiant.com/thermostatreplacementandmodif.htm

this is a trusted website of almost everyone in this forum and give stgep by step instructions. good luck!!

t walgamuth · #3 07-04-2006, 10:43 AM

on some models the aux fan does run when the engine reaches a certain temp. i dont know if this applies to the 85 or not.

tom w

SD Blue · #4 07-04-2006, 11:13 AM

What temps did it get to?

The aux. fan should come on at about 105C. But the normal engine driven fan should have provided enough cooling at those temps, especially, without a/c.

Did you have boil over or was it just registering hot on the guage? Sometimes, a loose engine-chassis ground strap or a loose connection at the temp. sensor (side of block, below injectors) can give erroneous readings.

(I'm not sure if that is the same sensor that controls the aux. fan. If you have better than dial-up, here is a website with the factory service manuals that may help: mb.braingears.com)

zman · #5 07-04-2006, 11:55 AM

Quote:

Originally Posted by SD Blue

What temps did it get to?

The aux. fan should come on at about 105C. But the normal engine driven fan should have provided enough cooling at those temps, especially, without a/c.

Did you have boil over or was it just registering hot on the guage? Sometimes, a loose engine-chassis ground strap or a loose connection at the temp. sensor (side of block, below injectors) can give erroneous readings.

(I'm not sure if that is the same sensor that controls the aux. fan. If you have better than dial-up, here is a website with the factory service manuals that may help: mb.braingears.com)

It pegged the gauge, but if you turn the heater on it cooled right down. I changed thermostat and it seems to stay around 90 on the gauge but the weather has not been as hot. I am going to change waterpump since car has pretty high mileage and I don't know if it's ever been done.

TheDon · #6 07-04-2006, 12:00 PM

the sending units you listed on the side of the head are for the temp guage and glow system.. the others im not sure... im having issues with my AC as well..

Jeremy5848 · #7 07-04-2006, 01:00 PM

Quote:

Originally Posted by zman

It pegged the gauge, but if you turn the heater on it cooled right down.

That suggests a partially clogged radiator or a malfunctioning thermostat. Check those before doing the water pump as they are easier and less expensive to fix.

If it got hot enough to peg the gauge (and assuming the gauge is working correctly, etc.) the aux fan should have come on. The fan in my 1985 300D Turbo comes on rarely, only on very hot days running around town with the A/C on. You can test the fan by wiring it directly to 12 Volts. If the fan is good then check the sensor that turns it on.

Jeremy