For those of you following my overheating thread, I finally managed to get my hands on a coolant system pressure tester.

None of the cap adapters seemed to work on the filler neck, they would hiss the second I started pressurizing with the pump. I used one of the corkscrew type adapters, and it seemed like it held better, but I could NOT get the pressure above 10PSI no matter how fast I tried pressurizing the system, and if I jarred the adapter it would lose pressure.

After it got to around the 10PSI mark, I started to hear coolant bubbling, and it was all being pushed into the overflow and started dripping onto the ground. I could not get it past 10 psi. The psi did slowly drop as well. Am I doing something wrong? I tried on the AST, and that pressurized to up to 14, but I don't think thats where you are supposed to test from.




Picture for how it was set up.

 

I think you may have answered your own question, but you always want to pressure test from the AST or wherever has the hose going to the overflow tank.

Pressurizing at the fill cap will increase pressure on the system until it pushes against the spring on the radiator cap, then the pressurized coolant will push into the overflow tank. This is working as it should, but that's why you can't use the fill cap.

Also, that fill cap has blue RTV gobbed all around it - that's REALLY not a good sign. That cap should seal with an O-ring with no RTV or anything involved.

Dale

 

^Oh boy, I agree on all that blue smurf snot. That’s trouble waiting to happen. Might be best to just call Ray Crowe and order a new cap/‘O’ring replacement

 

Now pressure test the system, at the AST. Should hold 13 psi for 15 minutes with little leakage.

 

In my experience, when pressure testing at the AST it can still be difficult for it to hold all the pressure, even if there is nothing wrong with your cooling system. Maybe it's poor sealing in the tool.

The benefit is that it will push coolant out of any leak points in the system, and on cars as old as this every hose is suspect.

 

Am I wrong in thinking he already found the problem? If he's pressurizing the system and the cap on the AST is failing to even reach 10psi before it bleeds off into the overflow tank; that's a freaking problem. That cap should hold at least 12psi or more (depending on what cap it is). If your system is constantly pushing coolant into the tank and not re-claiming it you'll definitely be in trouble.

Have you tried replacing the filler neck cap and also the AST cap? Cheap insurance if you haven't. You may also try cleaning the sealing surfaces of the cap and the neck where it seals against the cap.