Hello, My car overheats parked running. Not boiling over, but almost at the top of the temp guage. Here's the hard part. The cooling fan never comes on by itself .But it comes on with the AC switched on. Also I changed the radiator temp sensor. And if I jump the sensor wire connector The fan runs also. So I think this illuminates the wiring. Thanks Vern
the temp sensor should be the one at the bottom of the radiator. should be three wires. Unplug the connector and one of the three wires should have
12V when the engine is running. The other two are for turning on the fan on low speed or high speed (depending on the two-stage thermoswitch).Check for that 12V power first. If it's 12V, then take a length of wire and jump between that and one of the other terminals, then the other. Fan shoud turn on low speed for one and high for the other. If that all works, it's the thermoswitch that's bad. Otherwise, it's the wiring.
The fan coming on with the A/C is normal and at least means that your fan motor is probably good.
I agree with what Matt B wrote. Perhaps you could tell us what year the car is, as they used a few different configurations of the radiator fan over the years. On some A2 cars the thermoswitch at the radiator only has two terminals, and the rad fan has only a single speed. Others, as Matt describe, have three-terminal thermoswitches and 2-speed fans.
verndog wrote:
He has to have the three terminal switch since he said the fan works with the "AC" switched on.
If the needle on the temp indicator goes up to the red blinking light (not blinking of course) it's normal. Once it goes past the red LED, the thermo switch should come on around that time. Do not use the AC switch or you will never see it happen. Once it comes on it will stay on only when the engine is on since Diesel does not have a run-after shutoff feature.
What is happening is that diesels normally do not run hot all the time unless you are going full throttle on the highway or up a hill. If you just got done with a decent long run while the weather is hot, it will go above the typical temp indication of 1/3 to 1/2 the scale.
When you say "almost at the top of the temp gauge" I am assuming you mean above the blinking LED indicator (when you first turn the key it blinks). If the needle is in the middle of the LED indicator, wait a little bit until it reachs just above that and the thermo switch should go on. I think you are not waiting long enough and then you hit the AC switch which will cool the temp slowly. Just above the LED indicator should be ~198 deg F.
Using working AC will change the the Thermo-switch temp time and also make the engine work harder allowing for quicker temp climbing. This is only if the AC works and blows cold. The Thermo-switch should help out the AC at ~183 deg F.
Lastly. When you say overheats parked running. I am assuming that you mean after driving and parked for the info above.
If you mean parked and starting cold. Try this. Open the coolant expansion tank. Start up the engine, and then put your hand over the opening. Can you feel any puffs of air pressure or hear gurgling via the tank? If so, you might have a head gasket problem.
If it's warm outside, I can see it climbing while idle and not boiling over but you have to let it go up to and just above the LED indicator. If it goes a few needle widths past, I would say you have a problem then.
Having owned around 10 diesel powered A2's with ac I can tell you Peter is
100% correct. Diesel's don't normally get really hot. The only one I had that did actually had the radiator blocked with bugs. You could not see them but they were there. I replaced the head gasket for overheating and very quickly found it overheated sooner! While pressure washing the engine, I got the radiator by accident and bug bodies started coming out big time. The car never overheated again and lived a log happy life.JoBo
Can the rad get damaged by shooting pressurized water at it?
Within reason, no. A typical garden hose probably isn't going to generate enough pressure to bend the fins of the radiator.
Make sure you flush from the inside of the engine compartment outwards.
Hmmm...if the fan works on both speeds when jumped and if the switch is good (assuming it is since you replaced it), then I'm going to suspect a partially stuck thermostat. The dash gauge is most likely running off of a sensor near the engine for water temperature but the radiator's temperature isn't heating up enough to trigger the fan, so I'm going to suggest the thermostat is opening only enough to let some water into the radiator to get cooled but it's not allowing full circulation into the radiator so you have a borderline cooling situation that's fine when the car is moving but not fine when stopped. I say replace the thermostat and its o-ring....it's a cheap fix and it'll be good for years to come anyway.
What you call "3 wire water temp sensor" *is* the thermo switch.
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