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Hi,

Been chasing this problem a while.

Once engine gets to 140 degrees or over, I turn it off and it blows half the antifreeze out of the overflow can.
If I forget to turn on the electric fan, it will start blowing out in about 5 minutes of the engine running.

Car has been owned by 4 previous owners and no reports of overheating, BeCool radiator tells me a blown head gasket has to be it.

  • No evidence of any contamination in the oil or radiator.
  • No smoke coming from exhaust.
  • Used a block tester to check for exhaust gas in radiator, none.
  • Compression tests within spec.
  • Did a leak down test, no bubbles in radiator.
  • Decided to try a Dynamic Pressure Test on the engine and no idea what is going on there, see below.

Chevy BB, 396 6-71 Supercharger. 21-22lb cap as recommended by BeCool, mechanical water pump. Plugs all look normal.

In this video, the car was cold, first start in four months and it was 45 degrees, so hard starting as there is no choke on the carbs.
Comical to watch, but starts kicking over at 0:42, pressure goes down. 1:22 runs longer, and you can see pressure going down.
Rest of video shows same pressure drop and me just wrestling the engine to get some heat in it to get it running.

In this video I put some pressure in the system and same thing, pressure goes down.

My understanding is the pressure would go up if a head gasket was blown.
Is it going down because it is being cooled through the radiator or simply the movement to the fluid?
Is this normal?

Any advice before I turn it over to someone who knows more than I do?

Thanks,
Joe
 

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Greetings, sounds like you also have some other issues. That should start on first crank. Check to make sure you have the correct water pump. Some pumps designed for serpentine belts are reverse rotation although they look just like a older style BBC pump. Other issue may be head gasket, Cracked head or block. No easy fix. Good luck on your project.
 

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I can't give a whole lot of details on your issue but I for the first time did a pressure test on on my cooling system and was checking for a leak and mine was dead cold and not ran and it should be able to hold pressure by pumping and if it doe snot hold pressure and build up then you have a leak somewhere in your cooling system and even something such as a loose radiator hose can cause it to not hold pressure and be leaking.

I got mine only to go up to about 7 psi of pressure and my radiator cap is a 16 psi rated cap and as I got to 7 psi I started to hear a hissing sound and sure enough I had a loose enough radiator hose that is started to spit antifreeze out of it while being cold. As my engine ran and things heated up and expanded it would no longer leak. Then as I tried again my intake gasket pushed out some antifreeze and then I quit after that after not wanting to make things worse.

You should be able to build up pressure while pumping it but being careful not to go way past your systems max psi rating that your radiator cap rating is and what your system is setup for. I am sure someone else with a heck of a lot more experience will be able to post more.
 
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