Rotary4tw

iTrader: (3)

This afternoon I ran both a compression test: Compression Thread and also a coolant pressure test.

When I purchased my car about 2 months ago, we needed to drive it about 13 hours across country. It went through a large amount of coolant/water on the trip home, and the hot engine seemed to pump it out quite quickly near the end of the trip. (Stops every 45 mins to refill the system)

Since then, I have learned quite a bit about the coolant system, and have narrowed the problem down to an internal o-ring seal failure. The part that makes me a little apprehensive is the fact that I have little to no white smoke on startup (zero to 1 small puff), no coolant in my oil, and no coolant on my plugs.

I replaced the AST cap on my system, and it is rated for 16psi. I tested/replaced all connections from the AST to the overflow tank with clear tubing, and the system expanded, and appeared to retract coolant back into the system when it cooled down.

I finally got a pressure tester kit with the proper adaptor from Damian. Damian is the man, but most of you already know that. (FYI, the ones you get with the "Loan-A-Tool" program at AutoZone will not fit many import cars, and the adaptor is a $50.00 pep boy part)

Not knowing what to expect, I hooked the system up, and pumped 15psi into the system. (The cap is a 16psi cap)

At about 13psi, I could hear bubbling in the overflow tank, which means there was some pressure escaping the brand new ast cap. So either the tester is off a little or the cap is over-rated a few psi, I can deal with that.

When pressurized, the system slowly loses pressure at a rate of about 1psi per 6-8 mins. At first I thought it might hold steady and not slip, but it kept dropping. There are no coolant leaks anywhere, and the pressure kept dropping well below the 13psi mark. (Where I think the caps limit may have been)

This is all with a cold system granted. Next, while cold, I depressurized, and then hooked the tester up again to run the engine, and monitor how pressure would build up.

There are my results.

1 min -- 1psi
2 mins -- 1-2psi
4 mins -- 4psi
7 mins -- 7psi (Thermo opened at this point)
10 mins -- 13psi
12 mins -- 17 psi
14 mins -- 18 psi *System shut off at this point*

Also, my mechanical temp gauge is not installed yet, but the fans did not come on the whole time (thus sub 220 degs) and my temp stayed right in the "you could be f'ed and just not know it yet" range, which is the dead center for the stock water temp.

This tells me that the system seems to be abnormally pressurized for the temp that it was running. Anything above the 13psi mark was also likely pushing "x" amount of coolant out of my system into the overflow tank as well, and when the system cools, much less then "x" returns, causing the low coolant issues.

The other thing which is strange about my car which I can't seem to figure out the physics of... is that fact that normally, before all of these tests... my car would seem to only spill coolant after it was shut off. I would turn car off, 30 second turbo timer, and that would give me just enough time to put a little bucket under my 99 spec to catch the coolant that would drip out the overflow. What causes a pressure spike when the engine shuts off? If anything, wouldn't it stay constant or depressurize when the engine was killed?

In conclusion, the only test that I can think of that remains is the hydrocarbons test in my exhaust. At this point I'm convinced that there is a faulty o-ring. I was lucky enough to get a chance to meet Steve Kan last weekend and he was very kind and actually showed me what the inner o-ring looks like on an engine.

(It's the red inner seal for those of you who have not seen one before)



As always I appreciate the willingness and assistance from the forum, and look forward to getting this issue resolved.

-Rotary4tw