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steve · Guest

how can you tell when a thermostat is bad?

i think that the coolent is going through the bypass instead of through the head to cool it off.

does that sound reasonable?

steve

924 turbo · Guest

If the thermostat doesn't open at all, the water will just go from the block to the head and back to the block again. If it doesn't close, the water will go through the radiator when the engine is cold and it will take longer to heat up to operating temperature.

If the thermostat doesn't open, your cooling fans won't come on. Also, the hose that goes from the thermostat housing to the radiator will be relatively cold, even as the engine gets hot.

If the thermostat doesn't close, water will be circulating through the top hose when the engine is cold. You should be able to squeeze the hose when it is cold and feel water running through it.

The thermostat is pretty cheap, and if you have any cooling problems, it's probably best to replace it. Make sure to bleed air out of the cooling system when you do it. Just put the front of the car on jackstands or ramps and run the car with the bleeder plug out, making sure the tank has some coolant in it. Once coolant starts to flow out of the hose (not just bubble, but flow) put the bleeder screw back in and tighten it up. Then fill the coolant tank.