1987 Ford 302, new thermostat, water pump, radiator, and clutch fan. Heater core is bypassed temporarily to eliminate it from the equation. It won’t build pressure in the cooling system so I rented a coolant pressure checker. I pumped it up to 16psi with the motor cold and it held and didn’t leak anywhere. So, I started it with pressure still on it and it crept up until I bled down to 13psi where it held. So, I shut it off, bled the pressure off and restarted it hot. Letting it idle and reving it up it never builds pressure. I put cardboard under it and nothing is dripping. It only has an idiot light for temperature so I don’t know how hot it actually is. I’m scratching my head as I’d expect it to be leaking somewhere. Compression tested it and all cylinders are 170-180psi.
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Get the engine to operating temperature with the radiator cap off then shut it off. Put the pressure tester on it and pressurize it to 13-16psi then pull the spark plugs and use a bore scope to see if you have coolant in the cylinders.
Bad rad cap? Edit, I had to reread your post to realize your test bypass any cap failure. So i was thinking, is the pressure made from the coolant expanding? And if you bleed the pressure after its finished expanding, will it create any more pressure? Try warming it up from cold with the tester on it, starting with no pressure, and see if it makes pressure.
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Added a temp gauge and with it cold and the pressure gauge on it I let it get to temp which it stayed around 190ish. I could tell when the thermostat would open and close with the temp swings. It built and held 7-8psi in the cooling system. So, let it cool off till the next day. Put the cap on, let it get to temp and it had some pressure. I let it cool off and go to squeeze the upper radiator hose and hear water squishy noises around the cap and the overflow water level moving.
Signs point to a flaky cap I guess, so I’ll try a 3rd cap, maybe one without the pressure release this time for grins.
Signs point to a flaky cap I guess, so I’ll try a 3rd cap, maybe one without the pressure release this time for grins.
TrailTamer
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everything you said sound normal!
only way the cooling system will build pressure is if its sealed from cold to hot, via coolant's expansion.
only way the cooling system will build pressure is if its sealed from cold to hot, via coolant's expansion.