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Question DetailsAsked on 12/27/2011

My girlfriend drive a 1998 Chevrolet cavalier. There is a sensor on top of the engine that leak oil when you start her car. Anyone know why

Engine is a 2.4L. Sensor is on the outlet water housing

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2 Answers


Your question is a bit vague but I will try to point you in the right direction. The sensor you are referring to sounds like the coolant temperature sensor...Are you sure it is oil leaking or might it be antifreeze? General motors uses a coolant called DexCool and it is dark in color, sort of Carmel colored, rather than the typical green color. My other thoughts; a bad head gasket...does your coolant boil over or is their any antifreeze mixed in with the oil (your dipstick will have a white milky substance on it)? If either is true than it is likely a failed head gasket. Lastly, you may simply have a defective coolant sensor thats leaking.

Answered 8 years ago by Kevins Small Engine


You are sure this is a sensor - it has wires coming out, not tubing ? As other answer said - if a sensor on the water pump housing, almost certainly your engine coolant temperature sensor - may have one or two wires off it depending on whether you have a tempeature gauge or just an idiot light. I would assume the thread sealant has gone out - depending on where it is located, might or might not have to drain out a bit of coolant from the radiator to get that area above fluid level, then remove sensor and clean the threads and sensor tip, and put back in with some permatex sealant around the sensor threads - being sure not to get any on the tip or into the fluid. I can't see the sensor itself leaking - but if leaking around the wires, then needs replacing. If loose, just tightening it down might do it - but on't reef on it, likely threaded into an aluminum casting. Probably about 5-10 foot-pound torque spec. If a dome-shaped housing on the water pump that is leaking (usually no wires from it), that would likely be the thermostat - which commonly has a gasket under it which might be leaking. Same thing on lowering fluid level, remove and replace with new gasket. On some models the gasket HAS to be in there (I coat both sides with permatex to be sure) to provide clearance or the thermostat can jam up - on other cars you can just use non-hardening permatex as a gasket (non-hardening like red because this will likely need replacing at one or more times during car life, so easier to clean off at that time).
If it has tubing coming off it and is leaking at the tubing connection, could have a loose hose clamp or degraded hose, or could be line is plugged up and overpressuring - like if this is actually on the rocker cover rather than the waterpump housing and is a PCV valve or crankcase breather valve or such. If PVC valve, could also be the rubber insert seal in the rocker cover which the PVC valve shoves into and seats in has cracked or gotten old so it is leaking - though unless pretty shot would be just a weepage, not a flowing leak because there is no oil pressure there - just splash and oil vapor.

Answered 3 years ago by LCD

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