03 WRX overheats at highway speeds!!
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This is a discussion on 03 WRX overheats at highway speeds!! within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Sorry if theres already a thread on this but I've searched and searched for an answer. I have an 03 ...

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    Registered User neddy8823's Avatar
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    03 WRX overheats at highway speeds!!

    Sorry if theres already a thread on this but I've searched and searched for an answer. I have an 03 WRX Wagon and when I get out on the highway the temperature will rise when Im in 5th gear and before it gets to the red I either rev the motor or downshift into 4th and give it some gas and it creeps back down to normal temperature. Then when i go back to 5th gear it does in again??? I've read that the 03 radiators suck. Does anyone have any suggestions before I trying buying a radiator? I took the thermostat out and put it in hot water and it opened up.

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    I am thinking water pump. Perhaps the blades are rotted and not moving much water at lower RPM.

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    Resident meany-rator 06wrx4me's Avatar
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    Could be any number of issues.

    How many miles?

    Timing belt service with water pump been done?

    Have you kept up on your cooling system maintenance (replace coolant every 30k with factory coolant and deionized water)?

    That will help us narrow it down.

    But it could be:

    * Low coolant
    * Plugged radiator
    * Air bubble in the system
    * Malfunctioning thermostat (try a motorad failsafe one)
    * Bad water pump
    * coolant temp sensor
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    He simply abides. SD_GR's Avatar
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    Check for circulation. If not, take out rad and take it to a shop, it's cheaper than a pump. Do pump only as last resort. If you have circulation suspect leak.
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    Registered User neddy8823's Avatar
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    Timing belt and water pump were done at 92,000 miles and I have 125,000 now. The coolant has been changed a couple times in that time frame. I tested the thermostat in hot water and it checked out okay. I tried having the cooling system flushed at about 115,000 miles and it seemed to help for a little bit. Coolant doesnt turn a nasty color and theres none leaking into my oil which had me rule out the head gasket.

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    Pro Manscaper Mikie13's Avatar
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    System's been properly burped?

    I'd still think Thermostat or radiator though...
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    Quote Originally Posted by neddy8823 View Post
    I've read that the 03 radiators suck.
    03 Radiators suck only because they're known to crack. If your car is overheating and the coolant level is normal (and burped properly), it's not the radiator. As mentioned, I'd flush the coolant, and add new coolant using Subaru OEM coolant and Subaru Coolant conditioner. Before adding the new coolant, I'd check the thermostat and water pump. In all honesty, the fact that the car overheats at lower RPMs sounds like a water pump problem -- the water pump drives parasitically off of the timing belt.
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    Quote Originally Posted by neddy8823 View Post
    Timing belt and water pump were done at 92,000 miles and I have 125,000 now. The coolant has been changed a couple times in that time frame.
    Why?
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    Resident meany-rator 06wrx4me's Avatar
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    Quote Originally Posted by zax View Post
    03 Radiators suck only because they're known to crack. If your car is overheating and the coolant level is normal (and burped properly), it's not the radiator..
    Actually it still very well could be the radiator. The plastic radiators in current cars are known to become blocked overtime. These blockages effectively clog the cooling tubes and decrease the surface area that can dissipate heat. If the blockage gets large enough and close to the water pump side, it will actually restrict or stop the water from circulating causing pressure build ups and super heated areas.

    Plastic radiators can also not be boiled and flushing does very little to rectify the problem.

    I'd bet he has a 30-40% blockage in his radiator causing the issue.

    My brother in laws plastic radiator became so blocked it boiled the water in 1 end tank, created steam and blew a dollar bill size chunk out of the radiator.
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    zax
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    Quote Originally Posted by 06wrx4me View Post
    Actually it still very well could be the radiator. The plastic radiators in current cars are known to become blocked overtime. These blockages effectively clog the cooling tubes and decrease the surface area that can dissipate heat. If the blockage gets large enough and close to the water pump side, it will actually restrict or stop the water from circulating causing pressure build ups and super heated areas.

    Plastic radiators can also not be boiled and flushing does very little to rectify the problem.

    I'd bet he has a 30-40% blockage in his radiator causing the issue.

    My brother in laws plastic radiator became so blocked it boiled the water in 1 end tank, created steam and blew a dollar bill size chunk out of the radiator.
    Then why would the blockage cease at increased RPMs? The pressure does increase, but then I'd expect the blockage to either blow the radiator (as you have suggested) or cease altogether.
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    Resident meany-rator 06wrx4me's Avatar
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    Quote Originally Posted by zax View Post
    Then why would the blockage cease at increased RPMs? The pressure does increase, but then I'd expect the blockage to either blow the radiator (as you have suggested) or cease altogether.
    The water pump spins faster at higher rpms. Since the water pump is positive displacement, the flow increases as rpms increase. Thus at higher rpms, the velocity of the coolant moving through the tubes of the radiator (that aren't blocked) as well as the engine increases, improving the overall cooling systems effectiveness.

    Not to mention as rpms rise, road speed increases as does the mass flow rate of air through the radiators fins, increasing convection and overall system effectiveness.

    His symptoms are exactly what I have seen with blocked radiators in the past.
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    Registered User neddy8823's Avatar
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    Quote Originally Posted by SD_GR View Post
    Why?
    One time was to flush the cooling system and the other was to test the thermostat.

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    Registered User neddy8823's Avatar
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    Quote Originally Posted by 06wrx4me View Post
    The water pump spins faster at higher rpms. Since the water pump is positive displacement, the flow increases as rpms increase. Thus at higher rpms, the velocity of the coolant moving through the tubes of the radiator (that aren't blocked) as well as the engine increases, improving the overall cooling systems effectiveness.

    Not to mention as rpms rise, road speed increases as does the mass flow rate of air through the radiators fins, increasing convection and overall system effectiveness.

    His symptoms are exactly what I have seen with blocked radiators in the past.
    Awesome thank you for your help. Im going to try getting an aluminum radiator and see if a new one solves the problem!

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