jvandyke

Getting very strange behavour from coolant, the level changes dramatically from one drive to then next, sometimes not at all, coolant sometimes (usually) gets pressurized immediately upon start up.
Seems like a "soft" HG failure to me, one of the cylinders is applying compression to the water jacket via the HG, yes?
No other symptoms, no oil in coolant or vice versa, car runs well and doesn't over heat at all. No white smoke on start up or ever that we've noticed.
I'm thinking compression test and/or leak down test and most likely a HG job. Just seemed like a weird failure to me.

968workaholic

Sounds like the start of a bad headgakset. Compression/Leakdown test may not show it if its just starting to leak. I have a turbo motor head off right now for the exact same thing. No obvious damage to the sealing rings on the gasket, but it was severely distorted. Same symptoms as you are describing

GPA951s

Take a Quick look at the plugs, and the combustion chamber, Steam Cleans Very well! That's usually the Cheap and Quick way to confirm..

jvandyke

Pulled plugs a while back and all looked good but will do that again. My kid drives it everyday though only a couple miles at a time although it went about 30 Monday with no issues (other than erratic coolant levels). He wants to drive it no matter what.....good boy. But Dad doesn't really want to catch the fall out of blowing up this motor. I'm planning a HG R&R. We just did the oil cooler a couple weeks ago since it "seemed" like there might be some oil in the coolant and there was an oil leak from that area. That went pretty well and oil leak is gone, coolant looks fine (running pure water at the moment) but pressurizing and levels are unchanged by oil cooler seal job. Hopefully it's not a cracked something...

jvandyke

plugs all look good, compression is decent across all 4, did a "leak down" test and all we could get was a little hiss from the crankcase via the oil fill tube (getting past the rings I assumed).
Not sure I want to pull the head based on that. Gunna try again to really really bleed the coolant first but the fact that it (usually) pushes out water via the expansion tank immediately on start up (if the cap is off, cold engine) sure seems like compression from a cylinder, can't see any other means of that happening.

mel_t_vin

Why are you starting/running the car with the cap removed? Does it still burp coolant with the cap installed?

jvandyke

Running without cap to bleed it. I will occasionally burb it out with cap on after a run but seldom.
Did another bleeding session last night, made a bleeder fitting to run a hose to the (open) expansion tank, front of car raised a good foot, heater on hot, engine idling with sporadic revs. lots of aeration in the tube, bubbles from the tank itself, level would rise, rev engine, level fallls, refill, repeat sometimes rises right out of tank only to fall really low again and get topped off, did this for at least 10 minutes. No idea where all that water is going, no evidence of water vapor from tail pipe, pretty crazy, fan kicks in as expected, temp gauge says normal.
Using two different caps, it never releases pressure on it's own so it must not be excessive, I guess. Pretty crazy. I think we should just pull the head, no?

jvandyke

on advice of an x Porsche mechanic we drained off the pure water and added in about 70/30 coolant/water, the water was apparently boiling off which explains almost every scenario we had. 70 miles today and no worries, was it really that simple? Apparently.