Overheating 91 prelude si problem,

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I am starting to overheat at redlights and at idle. I replaced the thermostat and the temp sensor, but the problem remains. Today I noticed that steam and fluid is coming out of radiator cap, which I'm assuming is the problem. My question, is are radiator caps suppose to vent, or do I have a bad cap? I plan on replacing it tomorrow if possible. Thanks for your time...




  1. your radiator cap is not suppose to vent, it could be something simple as a bad radiator cap, over time your radiator cap looses pressue buy a new one at kragen or something its under 10 bucks, check your pipes make sure they have no leaks and check your coolant resevoir also to see if has any leaks or anything

  2. No, a radiator cap does not vent. It's supposed to keep the fluid under pressure inside and prevents it from coming out. Change the cap (make sure you only do this when the engine is completely cold...or it will come shooting out) and see if that fixes your problem. If it does not, check your fan, since overheating at a stop can mean your fan is not working properly, or not working at all. I'm about 90% sure the problem is probably gonna be the fan if it isn't the radiator cap. In fact it most likely is the fan because something has to make the fluid boil over in the first place, which is the reason why the cap is 'venting'. So definitely get your fan checked out.  If it's not the fan, then it just may be time to change the radiator. Which isn't unusual since the car is 17 years old, and if it hasn't been changed before, but most likely its just the fan.

  3. the radiator fan is not working. the only time the fan has an effect on cooling the engine is when the car is stopped or when the car is driving at speeds under 30 mph and the airflow over the front of teh car is insufficient to remove heat from the radiator.

    if you have air conditioning on the car, turn it on and you should see the temperature drop. turning the air conditioner on turns on the condensor fan which will then act as the radiator fan would normally and cool down the engine in traffic or at stops.  that is assuming that the condensor fan works.  you should hear it come on as soon as you turn the a/c on.  you can look at the fan behind teh radiator and you should see it running

    there are two possibilities with regard to why the fan is not working. most probably at that mileage is that the fan motor is burnt out. thats a 95% probability.

    the temperature sender that turns on the fan may be bad or the fan relay may be burnt out. the easiet test is to put 12v to the motor and see if it works. if it doesn't its the motor; if it does its the relay or the temperture switch

    the radiator cap will vent when pressure is over 15 psi.  your boiling the coolant in the radiator and that's creating more than 15psi pressure.  the cap is not the problem

    hope that helps

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