Hi all -

I've been having issues with the cooling system on this car. It started running warmer than usual, going up well above 100°C within about fifteen minutes of driving. I replaced the radiator and t-stat, but this hasn't helped. Upper radiator hose gets hot and the heater works well, so I assume the water pump is ok (?). I thought maybe I'd gotten a bad t-stat, so I pulled it out and let the car idle in the driveway for a half hour or so. Temp stayed around 80-90. This morning, I took it out (still with no t-stat), cool morning, and within fifteen minutes is was hitting 110 or so on the gauge. I shot the block, t-stat housing, and a number of other spots on the engine with an infrared thermometer and nothing read over 94°C. Fan seems to be working fine and all of the belts appear to be tensioned properly with no obvious slipping. I have not seen the aux fan come on.

Any thoughts on where to go from here? Is it possible that the temp sensor is reading consistently (in its own way) but incorrectly? I'm not sure of how to bleed these systems, so could I have left air in it? Should the aux fan be coming on after only fifteen minutes of driving? I seem to be running out of things to try.

Thanks in advance for any help.

Mike

The best way to bleed the coolant system is fill it nose high, through the upper radiator hose. Also, from my understanding of reading the FSM about the coolant system, the thermostat is needed for proper flow through the radiator.

The engine-driven cooling fan clutch takes care of the engine cooling. The aux fan is tied to the temp switch on the air conditioning system.

If your infrared thermometer is only showing 94C, then you may have temp sensor problems. It may be something as simple as a poor connection at the sensor. It should be the sensor located mid-way along the driver's side of the head. (Mine indicated temp problems after a valve adjustment. A little cleaning/tightening and back to normal.)

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Sam

84 300SD 350K+ miles ( Blue Belle )

Thanks! I'll pull the thing out and see how it looks.

I was thinking that it was located just aft of the thermostat housing, but it sounds like that's not correct?