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Question -
1995 chrysler concord. Overheats (immediatly, bad choice of words on my part) (WHEN ENGINE COMES UP TO TEMPERATURE, TEMPERATURE GUAGE INDICATES MOTOR IS HOT WHEN FLUID IS BLOWN OUT RESERVOR) and blows fluid out reservor. Engine head gascuts have been replaced, thermostat replaced by previous owners. This was an auction car i bought. Radiator Fan never comes on. where is sensor or relay for this. could this be only problem someone else overlooked? Can I bypass and have fan on all the time to see if this remidies problem before investing in additional parts?
Answer -
Hi Gary,
Immediate overpressurization of the cooling system (before the temp of the engine really gets sufficiently hot to boil the coolant) typically indicates that one of the two head gaskets has blown again or there is crack in the head or block that commuincates between a combustion chamber and the cooling system. I would suspect the gasket. You might check for water to be blown out of one of the spark plug holes:(NO SIGN OF WATER IN EXHUAST OR OIL) let the engine sit for a few minutes after it has self-pressurized, remove all the plugs (see if any one of them looks wet) and if not have a helper crank the engine and see you can spot some water to be expelled from one of the plug holes at the start of cranking. That will let you know which gasket is bad and where to inspect for cracks to be sure that just replacing the gasket again will not fix this. If I have misunderstood the symptoms, let me know, but as you describe it I doubt that the fan is the cause. The coolant may not get hot enough before the system over-pressurizes to heat the coolant temp sensor to the point where it alerts the computer to turn on the fan. The fan should turn on just by starting the engine with the AC system activated,( AC UNIT HAS BEEN REMOVED FROM CAR) assuming the AC system has refrigerant pressure. If the compressor is activated the fan will automatically come on regardless of engine temp. If it did, that would eliminate the fan and its relay as the source of your problem. It leaves unanswered whether the coolant temp sensor might not be working, but that quick overpressurization sure sounds to me like a combustion leak into the coolant system.
Roland
AnswerHi Gary,
Thanks for the clarification. I agree then that it is probably not a head gasket leak. It could be something very minimal like the engine coolant temperature sensor slipping off-value, or possibly a wire to it becoming open or grounded. That sensor is different from the sensor for the temperature gauge on the 3.3/3.5L engine so the gauge could detect overheat but the sensor be blissfully unaware and thus not turn on the cooling fans. So I would begin by checking the senor's resistance as a function of temperture of the system (using the gauge in the dash or a thermometer placed on the thermostat housing surface for reference). The thermostat housing is where the big top radiator hose connects to the engine, and immediately next to it, mounted vertically in the block is the sensor. It has two wires (black/light blue and tan/black) held in place by a plug that has a tab. Gently and slightly lift the tab on the plug to relase it from the tip of the sensor. Then if you have or can borrow an ohmmeter measure the resistance between the two contacts of the sensor as you allow the engine to warm up. It should be between 15,000 and 9,000 ohms at 50F and 80F ambient,respectively and then as the engine warms the coolant the resistance should drop to 900 ohms at 170F and 600 ohms at 200F. See if it appears to be working as it should. You may notice that the fans start running as soon as you have disconnected the sensor plug if the engine is then started or is operating at that moment of disconnect. That is normal. The issue is does the low speed fan run when the temp gets to about 210F or not when the sensor is plugged in, and the high speed fan should come on in addition when the temp hits aboutt 230F.
The other thing to check, since the fans never come on, is whether the fuse for the fans is open. This is located in the power distribution center under the hood, behind the battery against the inner fender wall. Fuse D is a 40 amp (blue) fuse located behind the frontmost fuse of the inner row of 5 fuses. Check to see that it isn't shorted or the wire fatigued by a subtle crack. That may be the only problem you have.
Let me know what you find out, please.
Roland
