[Fot] Coolant conundrum

[Robert Lang]

 The cooling of the radiator and temp spike seem to indicate an air bubble in the system. It could get there from spot temps causing localized boiling or it could come from a pressure leak from the combustion chamber or head gasket.

If you think you have a cracked head or bad head gasket, try pressurizing the system and see if the pressure holds. Stant makes a tool like, there are probably others, but buy or borrow this tool. It takes all the guess work out of such problems. My rule of thumb is to bring it up to cap pressure and see if it holds for at last 30 minutes (plus or minus a couple of lb is okay, but loosing half or more in less than 30 minutes is a dead giveaway.

I would also verify that the ignition timing is not too far advanced. Not that I ever had that problem. :-)
Note that you can also use the Stant gauge to verify "normal" system pressure - you want to do that to make sure your cap pressure will keep the coolant from boiling.
Good luck figuring out the problem.
Regards,Bob Lang


    On Saturday, September 23, 2023 at 02:05:24 PM EDT, Anthony Parker via Fot <fot at autox.team.net> wrote:  
 
  I'm having cooling problems.Need help being convinced that I have to do what I don't want to do.
Brand new short block, same old head, water pump, and radiator.

Over three trials, the engine will run fine and warm up with radiator hoses and radiator warming properly. Then the hoses and radiator will cool and coolant temp will spike to 230+. Radiator cold with sky high coolant temps.
Two more clues, hoses seem to pressurize very quickly and when I opened the radiator cap this morning (after cooling all night) pressurized air and coolant shot everywhere.
No thermostat and I have confirmed three times that system is completely full

Seems I have combustion gases getting into coolant and then bubbles eventually removing pump prime.
Don't know what else it could be.
Given the apparent direction of the leak, is there any use in trying some "stop leak" product?
Is it time to pull the head again to look for warping or gasket leak?
I suppose it could be a cracked cylinder, but this block has been checked by two different trusted engine machinists.
Desperately trying to get to the RunOffs, Anthony._______________________________________________
fot at autox.team.net

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