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I'm at the end of my rope here.
I installed a ball valve in my heater line while I had my heads off.
Got the new heads put on and started to refill the coolant system.
Thought I'd pressure test it first and I had a leak at my new ball valve.
So I took it out, tested it. Held 35PSI on the bench. No issues.
Installed in the car, leaks.
New silicone heater hose from block to valve.
Still leaks.
Removed the valve and installed a plain union.
Still leaks.
I have never had a problem with a coolant hose like this.
Any ideas?
I'm using lined hose clamps.
The ball valve has barbed NPT fittings.

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I’ve had similar problems when using silicone hose. The shop I bought the hose from suggested taking a scotch brite pad and roughing-up the surface the hose is being installed on. I recall thinking that was a dumb suggestion but it worked! It didn’t take much roughing-up either.

You should also be using a vacuum filling device, when filling your cooling system.

Last edited by davidnunn

Thanks guys. David, I got one of those vacuum filler kits based on feedback here.
So my problem was two problems at once.
The heater valve was probably just not tightened enough. After removing and replacing it 5 times I finally realized that the air I was hearing escaping was from the thermostat to swirl tank hose which is close enough to the heater shut off that  that's what I thought I was hearing. Holding steady pressure now!

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