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Overheating after head gasket, radiator flush, and new thermostat.

I recently replaced the head gasket, flushed the coolant and checked for blocked cores, and replaced the thermostat. Unfortunately, my car (2003 Mitsu. Eclipse 4 cyl) still overheats, though not as much.

Last night i took the thermostat out and drilled a TINY hole in the housing to allow for the passage of more coolant. It still overheats. Would enlarging the hole help, or should I budge for the new water pump?

Also, could belt tension have any effect on the performance of these parts? I'd never replaced belts, and was unsure of the whole process...


  • edited February 2010
    Enlarging the hole will not help. Under what driving conditions does it overheat? i.e., idling, high speed, etc.
  • edited February 2010
    Make sure you electric fan is working properly. Temp sensor in the radiator could also be the problem. Even if the radiator is flowing properly, if the sensor has debris around it, it cannot read the correct water temp.
  • edited February 2010
    it overheats after it has been running. the harder it's driven, the quicker it overheats, though it generally doesn't reach higher than about 3/4. idling doesn't affect it much. Running the heater brings it back down to normal operating temperature.
  • edited February 2010
    The fans have been checked. I cleared the sensor and checked the fluid last night while working on it. Also made sure the system was bled.
  • edited February 2010
    Also, if it does turn out to be the water pump, as long as I am not overheating (assuming i find a work around) there will be no damage to my vehicle, correct?
  • edited February 2010
  • edited February 2010
  • edited February 2010
    What is the idea behind the hole in the thermostat and why is it not standard on all new thermostats? It certainly can't allow that much more coolant to flow, I can see it being used as a way to prevent a blockage due to air in the system (which should be able to be bled normally).

    I have heard of the DIYer doing the "hole in the thermostat" thing for 30+ years but no professional mechanics (at least that I knew) ever used it.

    OP, myself I think you have a headgasket sealing problem that allows exhaust gases to contact the coolant, even in the smallest amount, or a cracked or not flat head.
  • edited February 2010
    Water pump flow is easy enough to check. Usually, what you need is a new radiator..
  • edited February 2010
    I just replaced the head gasket, and made sure of it's sound placement.The hole is to allow more coolant to pass through the system, though it was mostly me grasping at any possible solution.
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