Testing new cooling system only with air

BelairBelair Member Posts: 3
edited October 2018 in General
I have a newly rebuilt sbc (from a reputable auto machine shop) with all new cooling system components. I pressure tested the cooling system to 16 psig only with air and no coolant and am leaking approximately 1 psi a minute, then finally to 0 psi. I checked all connections with soapy water and couldn't find any bubbles indicating leaks. I even bypassed the heater core, but it is still leaking. Hope the leak is not internal to the engine.

Is it correct to test with air only. With the viscosity of water being approximately 100 x more than air, will I be okay to add coolant and start the new engine, or should I test some more?


  • Mr_ShiftrightMr_Shiftright Member Posts: 64,481
    I'm not sure why you are trying this without coolant. The whole point is to use the coolant as the indicator.
  • BelairBelair Member Posts: 3
    I was thinking, testing with air (using a Stant tester) would be a lot cleaner to fix any leaks rather than with coolant added. I am planning to add coolant this weekend if I don’t get any other comments to do otherwise
  • Mr_ShiftrightMr_Shiftright Member Posts: 64,481
    Well as you can see, even though there *might* be a leak, you can't find it using the air method, but with coolant in the system, it should show up right away. Use a pressure tester on the radiator opening, and pressurize to radiator cap pressure or a little higher. If there were a head gasket leak, you'd be able to pull a spark plug and see coolant on the plug.
  • thecardoc3thecardoc3 Member Posts: 5,697
    You can use air pressure to try to locate a leak, but unless it is big enough to be heard or detected with soapy water you need to add something like this to your routine. http://www.skf.com/us/products/condition-monitoring/basic-condition-monitoring-products/ultrasonic-leak-detector/index.html

  • BelairBelair Member Posts: 3
    Thanks everyone for all your comments. I will add coolant and start up the new engine. Thanks thecardoc3, I’m familiar with the ultrasonic leak detectors. We used it for leak tests on industrial compressed air systems.
  • thecardoc3thecardoc3 Member Posts: 5,697
    edited October 2018
    We do use them to help find leaks in things like evaporative emissions systems. They help with door and window seals, water leaks. And yes, for testing for leaks before installing a rebuilt or used engine or transmission. etc.
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