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I am having a odd overheating problem with my 2010 subaru impreza. As far as i know when i got it the head gasket, timing belt, water pump where all replaced. I have since changed the radiator, thermostat, upper and lower radiator hoses. I have bled the system of air with a spill free funnel when the front of the car was elevated. I have used a block tester to check for hydrocarbons in the coolant which always comes up clear fluid stays blue. I have used a ir temp gun to make sure the thermostat opens and closes normallyand the fans work normally the system keeps pressure and draws fluid back from the overflow when the engine cools off. i have no lack of power and a couple of months ago changed the plugs and wires and checked compression. but it is not an all the time problem i can drive an hour plus one day with no problems but later in the day a 5 min drive will cause and overheat. I am wondering if anyone has any ideas at all about this since all that is mostly left is to pull the engine apart.
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Did you replace the thermostat with the Subaru (OEM) thermo? Subies are very picky with their thermostats. Also, air in the system. Sometimes it can be very tedious to get all the air out, requiring many burpings. If the cooling system checks out fine, the only thing left causing this would be a faulty head gasket.
+1 on flaky aftermarket thermostat. Have you IRed the hoses when the overheating is happening?
Also, I’d consider the possibility that the water pump may have been replaced with the Chinese POS that comes with the Gates kit rather than an OEM or Aisin pump. Unfortunately no way to tell without pulling the whole mess apart.
I’ve always found Subie coolant systems very easy to bleed, given your description I doubt it’s air. I would either wait for the next overheat and IR the hoses, or maybe just go ahead and swap the thermostat to minimize risk to the head gaskets. Though it’s not the easiest of thermostats to replace, you have to drain the block; you can save the coolant in the rad by pinching the lower hose. Make sure to use OEM coolant.First question …
When you state : ” a 5 min drive will cause and overheat.”
How do you determine it is over heating?
Are you reading the dash board gauge or do you witness steam coming from under the hood?Second question:
When you determine it is overheating, have you tried to turn the cabin heater on full and see if the overheating subsides?It may be your looking at a faulty temp sensor, wiring or gauge issue.
yes i have used a subaru thermostat and radiator cap when i replaced them. I also burped the system several times letting the fans cycle 3-4 times before i stopped and put the cap back on.
I don’t use aftermaket parts the only non oem parts i used was the upper and lower radiator hoses. i had to replace my ir gun and since i got it have not had an overheat. I only know that there is a gates sticker in the engine compartment.
a 5 min drive sometimes would cause an overheat. that is the odd part it does not happen all the time. and when an “overheat” happens it would have the dashboard light come on and cause the overflow tank to fill a lot. and a couple of time would even pop the cover of the overflow tank. and no from the times it has happened turning the heat up full does not change anything. but letting the car sit over night it will pull the extra fluid back into the radiator and might be perfectly fine the next day
i have replaced the cap twice since i got the car also from what i understand if the cap was not working right the system would not be under pressure and be unable to draw fluid back in when it cools off if the cap was bad.
by the temp light either blinking red or staying red and increased filling of overflow bottle with bubbles
yes i have and at most the fluid changes from dark blue to a little lighter blue the only time i got a green was because the fluid bubbled up and got sucked in. I checked the fluid to make sure that it was working by putting it near the exhaust and it changed bright yellow
The Subaru cooling systems are a pain to bleed the air out of. I think you either:
1. still have some air in the system or even some debris that is significantly retarding coolant flow through the engine
or
2. combustion gasses are leaking into the cooling system when the engine gets hot.
I would flush and refill the whole system again. When refilling remove the top radiator hose until coolant comes out and then refit, fill and bleed.
If the head has been off the engine as you believe (probably because the previous owner over heated it and blew the head gasket) they probably never had the head machined before refitting.
If it is not item 1 then it sure sounds like combustion gasses getting into the cooling system.
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