Bubbles in coolant, but pressure/block test ok?
 

I have a '93 with a rebuilt engine from Jan. of this year. Upon starting it one morning, I got the "Add Coolant" light. Turns out the overflow was empty also. Suspecting an o-ring failure, I checked for bubbles in the coolant while the car is running and, lucky me, they are there.

As a double check, I had the cooling system pressure tested. It turned out ok, no pressure loss. Then I had the block test done (checking for fuel fumes in the coolant), and it came back clean.

So now I have two tests that say the engine is fine, and one that says it needs to be rebuilt. Anyone know what might be going on?

Did you notice any coolant leaking? I assume it went out onto the ground somewhere since you said you aren't leaking any through the coolant seals.

Some people have had cracks in their overflow tanks and needed to replace them.

I did find a small leak early on in this process. It's fixed now and I'm still seeing the bubbles and I need to top off the coolant fairly often.

The coolant seals can be bad without coolant entering the combustion chamber. The combustion chamber is under quite a bit more pressure than the coolant and air from the chamber can be pushed into the coolant causing overheating problems. I have an engine that is fine until you start to boost it and then the temp guage goes up like a rocket, only to come back down quickly after the event. These engines are piles of $%&#

Check the water pump, just under the pulley there is a little bleeder hole, that could do it there..

Jason

Do you know the water temp?
 

Presure test radiator (plastic end tanks don't last)...ssuming it's stock.

You can remove some air from the horizontal hose that connects to the throttle body, close to the firewall. Hold the hose strait up and bubbles will float out. You will loose coolant (onto the engine & floor), reconect the hose and shut engine off. Refill radiator with Royal Purple Ice and if still not full then distiled water.

Check plastic AST. If it's busted, you'll see coolant seeping through the crack were it was glued together (sorta like a green stripe).

How long did you leave the pressure tester on for?

You really need 24 hours minimum to see if it holds.

The engine needs to be stone cold to test.

Regardless, if you have champagne bubbles in the filler neck you have bad o rings. Sorry.

The pressure test maybe ran for a half hour, an hour at the most. I can see how this test would turn out ok since it's not that much pressure compared to the combustion chamber pressure. The block test though should have indicated combustion gases in the filler neck. Maybe I have a small amount of bubbles and the test wasn't sensitive enough to catch them.

BTW, I have no AST, no coolant leaks, water pump is new.

I'm screwed.

First indication of O ring failure can be the sudden rise in temp when the engine is under boost. If yours does this when hard driving then you must suspect air entering the coolant system causing a hot spot in the engine , usually very close to where it is leaking. Block weld willl not cure this problem, as it only cures the reverse where coolant leaks into the combustion chamber. I have removed my thermostat mechanism in order to keep the engine at a cooler temp, so when it does this it has a longer way to get to the hot zone. This will only prolong the death of the interesting but @$*@@(* unreliable 13BREW. When she goes the FD will be recieving the supercharged LS1 directly from GM.