Question about Subaru Forester

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Car is overheating at high speeds. thermostat is out radiator and engine flushed out. what is teh problem

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  • urmuddermank Jul 22, 2009

    we took out the thermostat because we thought it was stuck. we flushed out the radiator an the engine. i cleaned out the resevoir by the intake manifold. i saw that there i a leak on the overflow bottle line from the resevoir where it joins at the fitting. we just cant seem to figure out wat is the problem

  • urmuddermank Jul 22, 2009

    the fans are coming on normal. we are not losin water, we changed the radiator. opened teh top an flished it out an sealed it back. pressure tested for leaks an none was found. wud clogged heater lines even though the heater isnt on cause this? or an we live in tropical climate.

  • urmuddermank Jul 22, 2009

    we checked the water pump an it is in gud condition, water is flowin. how cud teh hose collapse even though it is at a high pressure at high speeds?

  • urmuddermank Jul 22, 2009

    will try this

  • urmuddermank Jul 22, 2009

    no we didnt run teh heater on we just bled it normal, we normally take out the heater lines an plug them because we dont use it down here in trinidad. but if it is not on wud it still cause this problem?

  • urmuddermank Jul 22, 2009

    but th eting is we dont turn it on period so it shudnt be open to get an air lock. so i dont see it as a problem

  • urmuddermank Jul 23, 2009

    i will try the heater bleeding in the morning wen i go to work. it worth a try

  • mike loshbough
    mike loshbough May 11, 2010

    what do you mean the thermostat is out?

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  • Subaru Master
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Check for a soft spot in rad hoses, especially lower if it's going to water pump. If they have a soft (easy to squeeze together) spot, it will possibly be collapsing at high speed, and cutting of proper flow. Water pump flow looks good?

Posted on Jul 22, 2009

  • 4 more comments 
  • Mike Butler
    Mike Butler Jul 22, 2009

    Don't forget, your pump is pulling coolant usually upward at high speed, which creates a vacuum like condition at that hose, and everything else is sealed until thermostat opens right?

  • Mike Butler
    Mike Butler Jul 22, 2009

    Put thermostat back in. No heating up at idle? Try running down highway & when hot, turn heater on high temperature & high fan & see if temperature goes down. Let me/us know.

  • Mike Butler
    Mike Butler Jul 22, 2009

    When you did all the work on cooling system, you did run engine quite a while with heater on while refilling coolant right?

  • Mike Butler
    Mike Butler Jul 22, 2009

    Heater is a good spot for airlock if not turned on when bleeding system. If you just bypass heater core, (join 2 lines together) it should be o.k. . Up here where we need our heaters in Canada, those who forget to turn heater on when bleeding cooling system, experience airlock quite often which causes overheating on highway. Even experienced mechanics have rushed through it and suffered the same results.

  • Mike Butler
    Mike Butler Jul 22, 2009

    Unless your system has a flow control valve in the line, it will still circulate though the heater core. It only takes a few minutes time to bleed system with rad cap off & heater on, and let rad fan come on 2 or 3 times before putting cap back on. Besides, down there, the extra coolant running through heater core etc, would provide a little extra protection. Your only going to feel heat if heater on, if all controls work properly.

  • Mike Butler
    Mike Butler Jul 23, 2009

    Yah, keep me posted & don't forget to try turning heat on high & high fan if heats up, just to see if temperature comes down at all. When heater core in, heat on, & fan on high, heater core actually acts like an extra (small) rad & blower acts as a small rad fan to help cool engine coolant temperature slightly. That method got me home a couple of times when overheating due to partially plugged rad. That's why if it does heat up & turning all that on helps cool engine, then I'd replace rad.

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  • Subaru Master
  • 1,779 Answers

You say the thermostat is out, if you mean there is no thermostat at all, you must replace it, as the engine must maintain a specific temp to run properly. The cars computer relies on input on engine temp for fuel mixture, and all engine functions. Are the cooling fans going on as engine temp rises. If not, let me know so I can try to help further. You may have a defective fan switch or fan motor.

Posted on Jul 22, 2009

  • Curt Downs Jul 22, 2009

    I agree with motor 1258, even if never use the heater, there can be air in the system if not turned on to circulate to remove air. Not sure why you won't try it?

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  • Master
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Partially clogged radiator

Posted on Jul 22, 2009

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