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Thread: Cooling System Pressure Testing Question

  1. #1
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    Cooling System Pressure Testing Question

    I recently bought a cooling pressure tester kit because I had a leak near the back of my engine bay and thought it might help pinpoint. The kit did help but when I drove my car after pressure testing the cooling system it overheated. Was I supposed to bleed the system after I did the testing? (This might be a super dumb question lol)
    I am re-bleeding the system regardless but I am super cautious because that was the first time I overheated and I have heard all the stories of air pockets blowing out head gaskets.

  2. #2
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    You must have had air in the system from that leak. Pressure testing it may have made it leak out when you pressurized it. Things are a little different when pressurizing the system with air, normally the engine is hot and things expand and may leak slower, when the car is cold and you pressurize it it could leak faster.

    You should make sure its rock solid before going on long drives or getting the engine super hot when driving the car hard. Let the car fully warm up and the fan should cycle. If the fan doesn't cycle it could be because there's air in the radiator (bad expansion tank). If your sure the tank is good then you can warp a rag around the fan temp switch on the side of the rad, this will allow the fan to come on sooner. Another thing to try to get the fans to come on is to raise the rpm to around 1500-2000k it shouldn't take long to get the temps up. Another possibiltiy is that something is wrong with the aux fan system (fuse, relay, switch, fan) could be bad.
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  3. #3
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    I wouldn’t spend my money tracking down a leak. Just do one time maintenance your car probably needs it anyway. Radiator, hoses, expansion tank, heater core and head gasket with ARP hardware for peace of mind. All can be done for around $500 and a weekend of your time a day if you have a friend. I don’t have friends so it takes me a weekend lol


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  4. #4
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    Quote Originally Posted by Eric93se View Post
    You must have had air in the system from that leak. Pressure testing it may have made it leak out when you pressurized it. Things are a little different when pressurizing the system with air, normally the engine is hot and things expand and may leak slower, when the car is cold and you pressurize it it could leak faster.

    You should make sure its rock solid before going on long drives or getting the engine super hot when driving the car hard. Let the car fully warm up and the fan should cycle. If the fan doesn't cycle it could be because there's air in the radiator (bad expansion tank). If your sure the tank is good then you can warp a rag around the fan temp switch on the side of the rad, this will allow the fan to come on sooner. Another thing to try to get the fans to come on is to raise the rpm to around 1500-2000k it shouldn't take long to get the temps up. Another possibiltiy is that something is wrong with the aux fan system (fuse, relay, switch, fan) could be bad.
    From what I can tell all the fans are working good, this is the first time the car has ever overheated on me, so I was just assuming the pressure tester stuck some air in there. I did some maintenance a few months ago which included replacing the expansion tank so hopefully there is nothing wrong there. I will double check everything though! Thanks for the advice!

  5. #5
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    I recently replaced a lot of the cooling system in the front, I still probably need to replace the head gasket though. Head gasket is a lot more daunting for me though since I am really new to working on cars.

  6. #6
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    I bought one of those cheap 26 dollar eBay expansion tanks and it was leaking air all the way around the top hat but would not leak it took me forever to figure that out check there especially since you just replaced it.


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  7. #7
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    eBay unit after 2 months it literally exploded


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  8. #8
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    Hmm weird my other response isn't showing.
    Thanks though! I will definitely double check!

  9. #9
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    Have you replaced the water pump , it should have been part of your coolant maintenance, what about your thermostat ?
    I make a habit of testing a new thermostat before installation , it takes 5 minutes to boil some water and drop it in.

  10. #10
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    Head gasket? Seriously people.

    Yes, if you pressure tested it and it has a leak you need to bleed the system again, especially if you tested it on the flat or nose down.

    Do that and report back (if you need to).
    '96 M3, S50B32, 6MT
    + good stuff

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