Dale1990

I finally buttoned up my engine after replacing the lower manifold gasket because of a coolant leak. Boy, is it nice to hear that engine again!

Anyway, after a quick run around the block to get it up to temp and make sure it was full of coolant, I decided to put the pressure tester back on to double check the repairs. I pumped it up to 16psi (1psi under the cap rating) and did not see any external leaks (Whew).

How long should the system hold pressure? an hr? a day?

Its only been on there for about 10min w/ no drop so far.

BTW: Thanks JAKE for the great write up on the gasket change. It helped quite a bit!

- Dale

Dale1990

Well, at 15 min-ish it is down to 15psi Hmmm...

xs650

Jake, I don't have a time criteria for you, but be sure to do any tests longer than a few minutes with the engine and coolant at a relatively constant temperature. As things cool off, pressure will drop some, even if there is no leak.

It also makes a -big- difference if the system is full of coolant or not.

FWIW, my 96 factory shop manual just says to pressurize and look for leaks. It doen't give and pressure drop criteria.

That could be because leakdown time would be a function of how much air is in the system. They may not be able to give a meaningful time.

Dick

Dale1990

Good idea about the temp/pressure falloff. I forgot about that. The cooland is still warmer than ambient so that might be part of it too.

Also, I found a hose clamp that wasn't tight enough on the top of the radiator under the shroud - nice idea of GM to put an access hole in the shroud.

I pumped it back up to 16 and we'll see.

Thanks

- Dale

xs650

I hadn't thought about cooling system pressure tests much before. If you have your system completely full of coolant, the pressure supply when you pump it up is only coming from the little bit of air you pump in and the stretch you put in the hoses.

JAKE

If you have a leak, you'll know it right away because the pressure will not hold.

So if it's holding, you're good to go.

Just as a precaution, after a few heating and cooling cycles, recheck the torque on the intake manifold bolts. A few heating and cooling cycles sometimes results in a loss of bolt torque.

After re-torquing any that need it, the torque should hold from then on. Same thing with header gaskets and head gaskets.

Jake

Dale1990

Well I found 2 more hose clamp leaks. One from a GM clamp that has seen better days and one from a clamp of mine that was not tight enough.

With the system under pressure like this it really make it easy to find these tiny leaks. The two I just fixed were small enough that I would probably never notice them under normal circumstances.

As an aside, does anyone know the "normal" pressure the system is under? Maybe at 200* or so temp?