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Thread: Idles fine, overheats when driving

  1. #1
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    Idles fine, overheats when driving

    I have a 2002 325i that's having cooling system issues. I have replaced the thermostat, water pump, expansion tank and neck, all hoses, radiator, put new o-rings on temp sensor. And probably more. It idles fine for 30+ minutes but as soon as I drive it more than about 2 miles it starts to heat up and build pressure. I've tried everything that I can think of. No white smoke and no water in the oil. So I think my head gasket is fine? Any ideas?

  2. #2
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    Follow proper bleeding procedures.
    If still no improvement,
    have a cylinder leakdown test performed.
    Last edited by MIKYZZ4; 02-11-2018 at 04:33 AM.
    A jack of all trades, master of none.

  3. #3
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    Thank you. Do u have a proper bleeding procedure that you recommend? I've tried several and not 100% sure if any of them is correct or efficient.

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    A jack of all trades, master of none.

  5. #5
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    What brands of parts did you install? Aftetmarket cooling system parts are VERBOTEN as the cooling system is the E46’s Achilles heel.

  6. #6
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    Quote Originally Posted by Dcbean55 View Post
    I have a 2002 325i that's having cooling system issues. I have replaced the thermostat, water pump, expansion tank and neck, all hoses, radiator, put new o-rings on temp sensor. And probably more. It idles fine for 30+ minutes but as soon as I drive it more than about 2 miles it starts to heat up and build pressure. I've tried everything that I can think of. No white smoke and no water in the oil. So I think my head gasket is fine? Any ideas?
    Please do not be offended by my suggesting this, but are you sure you have enough coolant in the system? I had a Lexus doing this and it turned out I needed to add coolant. Thought there was enough, but there wasn't.

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  7. #7
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    I checked coolant level and it's good. I actually was convinced it was a cracked head or blown head gasket but I did a compression test and used a block tester and everything came out normal. No combustion gases in radiator and no leaks. I am at a loss at this point. I just can't figure it out. All replaced parts are new but purchased mostly at O'Reilly's auto parts. They weren't cheap by any means but maybe I should question the quality as MarcoZandrini mentioned above. As of now, still idles for as long as 30 minutes without incident until I drive less than 2 miles and pressure builds up very quickly and I have to stop before it blows something to relieve that pressure. Thanks for all the responses. I will update if I ever figure this out. For now, I'm in a rental just to go to and from work. Thanks again....

  8. #8
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    That sounds like a headgasket leak.
    Top off coolant so you can easily observe bubbles,
    then perform a cylinder leakdown test to confirm leak.
    A jack of all trades, master of none.

  9. #9
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    I'm bleeding it again right now and it seems tons of air is coming out. In the past I didn't have heater on hot with fan on high. But I am still only getting cold air from heater. It just now went up to red on temp Gage and I added water , it immediately went back down to normal and heater got Luke warm.

  10. #10
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    Still never got more than Luke warm heater. Doing another block test while it's hot.

  11. #11
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    Due to the compressed air/gasses being infused into coolant passages.
    LEAKDOWN TEST
    A jack of all trades, master of none.

  12. #12
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    A jack of all trades, master of none.

  13. #13
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    I agree with you on the leakdown test. I'm gonna have to bring it down to a shop or buy a leakdown regulator tool. Either way I think that's the answer at this point. Thanks so much for your input.

  14. #14
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    Block test still showed good even after I tested when hot. Go figure.

  15. #15
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    Installing aftermarket cooling system parts in an E46 is verboten. Why? They’ll fail and you’ll end up either redoing the work with quality parts OR you’ll end up with an overheated engine.

  16. #16
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    Thank you MarcoZandrini....I'm investigating that now.

  17. #17
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    Staying cool at idle and heating up while driving is a classic sign of a clogged radiator

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