blitz

You know... (long pause)... all I can say is that something in that airplane article just clicked in my head, and when I woke up this morning the answer was there. How such a small amount of air trapped in the ends of those little hoses caused all that relentless boiling in the rest of the system I really don't understand, go figure. I don't think I did any damage, but having said that, I don't think I did my motor any favors either. It's the localized boiling of coolant off of the surface of the jackets which surround the cylinders that effectively reduces actual coolant contact with the jacket, so the bore temp would rise to some degree. I think the cooler 'stat may have been my saving grace by way of greater opening and flow. Not once did the block temp ever rise into an overheat condition. That appears to be what the author of the article did. He tapped petcock(s) into the crossover pipe.

I'm hardly out of ideas!!!

Uhh... not yet, just gimme a little more time. Hehe

I had previously done the throttle body bypass mod on my vehicle, but incorrectly. Instead of reconnecting the removed hoses to each other, and allowing trapped air to move through, I had capped them off, so a small amount of air was held captive in the ends of each hose, and that's all it took to mess up the balance in the cooling system. I reconnected the hoses to the TB, drove the car up on ramps, burped it out, and voila; normalcy. Thanks to everyone who helped. Texan, don't worry 'bout the rad-cap, now I got a replacment on hand. The original ain't gonna last forever.

Japanese vehicles appreciate a silicate-free or at least a low-silicate formulation in order to preserve the life of the water pump seal. Also avoid a full organic OAT (e.g. DEXCOOL) type. Other than that, the brand-name shouldn't matter. Here's a link to an article that'll thoroughly confuse you: http://www.vectorbd.com/peugeot/archive/99_8/0415.html

Today's my day off, so I spent some time doing searches on Subaru cooling system phenomenon. Found this quote to be interesting: (it's from an aircraft conversion article) "The 2.5 liter Subaru is sensitive to air bubbles in the coolant. It only takes about 1/2 cup of air in the engine block to cause heat transfer problems. This engine is particularly sensitive. Trapped air is easily 10 times more significant than any other cooling parameter. It's pretty conclusive that trapped air causes local boiling in the block. This affects the entire cooling sys and rapidly degrades heat transfer." "During initial ground testing I did multiple high speed taxi runs. I would see the coolant temp elevate after each run. It would get to the boiling point after 4 runs down the 5000 ft runway. If I continued, the cooling sys would boil over. I deliberately did this many times. If I aborted any further runs, then after shutting the engine down I could hear it gurgling. This was the fluid boiling internally. " "All of these problems were caused by a small quantity of air trapped in the block at the highest point. Eventually, I added a small diameter tube to this block high point. This allows all the air to exit the block and move to the small reservoir under the radiator cap. Unfortunately, all of my deliberate overheating caused the heads to warp. This allowed compression gasses to flow into the cooling sys during high power settings. My computer detected this problem. 3 seconds after applying full throttle, the coolant pressure would rise to 24 psi. It would then slowly drop 5 seconds later. " "So trapped air causes head warp, which causes air to enter the cooling system. It was pretty amusing that at the same time I discovered this entrained air sensitivity in the 2.5 engine, so too did the auto dealers. Head warp caused by customers changing their coolant is now the number one warranty item with this engine. All caused by an engine block that was not plumbed to dynamically remove air from the high point. Subaru has since changed their cooling system design. " "It's essential that the 2.5 liter coolant crossover tube atop the engine be drilled and tapped. This allows user to add a small tube from there to the coolant reservoir. Any air inside the engine block then automatically purges. Proof of effective purging is that I can now drain all the coolant from the entire sys, then refill. Every drop can be refilled without hesitation. Before adding this air purge, I would end up with a few cups of fluid that I could not get back in to the system. Also, I now can't get the engine to gurgle after a hot shut down. " If I'm reading this correctly, the author's claiming that the phase I head-gasket problem is directly attributable to a small quantity of trapped air.

Yeah I did actually wipe it out and it's spotless. No nicks in it or anything. Likewise the cap has no flaws in the rubber seals. I lifted up the little back-flow check valve thingy to check for possible detritus and none found. I think it's the correct cap. All the visual dimensions are identical to the original part as is the labeled pressure. The parts guy used my VIN# to establish the part I recieved. I'm wondering if the bubbling is just a normal phenomemon on this vehicle. There's a good chance that I'm just freaking out over nothing.

Regarding the "no pressure" thing, here's what happened: I put the new cap on at the dealer, drove home, opened the hood and noticed the expansion bottle right on the verge of frothing over with boiling coolant. I sqeezed the top hose and found no pressure. I mean absoutely zero pressure, the top hose was slack. So I removed the cap, let it cool a bit, put the levels in both the radiator and the tank back to normal while fast-idling it up to temperature, replaced the cap, burped it out, and let it cool again. Took it for a drive, pulling over every quarter mile or so to keep an eye on things as I built heat into the system. The frothing was gone and a small amount of pressure began to build (approx. 5 psi), but as I began to ratchet up the throttle application between stops, the bubbling described in my original post re-appeared. In essence, I appear to be back at my starting point. My Impreza manual calls for a 16 psi cap and that's what's installed, but I'm not feeling 16 psi (squeezing by hand) pressure building in the top hose (based on what I've felt on every other car I've owned). This defies explanation, as does the frothing episode. What's next? Hydrocarbon sniff test I reckon?

OK, I got Pep Boys, Autozone, and all the others two miles from my house, but instead I elect to go 8 miles to the dealer and get a Fujaru part. Now I got a cap on my car that holds absolutely zero pressure. :brolleye: Should I just shoot myself or what?

1 Lucky Texan & alias20035: Thanks for the insight. I'm gonna try a fresh cap tommorrow.

theotherskip, Nope, no oil residue in the overflow tank or any exhaust smell for that matter. Likewise I find no evidence of coolant or moisture in the oil. I had the plugs out last month to have a look-see and saw no "washing" on any plug. They all had a perfect tan coat. The coolant level isn't dropping any. Background on the problem: About a year ago as I was parking the vehicle after a spirited blast up the road, I heard a gurgling sound, like the water pump cavitating on air in the cooling system. Squeezing the top hose, I was able to force trapped air out of the overflow hose. Subsequently, any spirited blast would produce the gurgle and then the squeeze-air. So out of curiosity, I opened up the overflow yesterday and saw bubbles. The rad-cap is original, so I'll pitch in a new one Monday and see what happens. The thermostat was changed about five months ago to cooler zerosports unit (it's 13F cooler than stock).

'02 OBS 35,000 miles I'm thinkin' I got an internal head gasket leak, ...but on a phase II motor tho?!! I thought the phase II's were prone to the external leak. The irony is I think this has been going on for close to a year, but I just didn't piece it together until this morning. The thing's not overheating or showing any fluctuations in the temp gauge. It's actually been running great. Anyone else heard of an internal leak on a phase II?