sunflow99 Posted September 15, 2004 Share Posted September 15, 2004 When I changed out my thermostat, I just refilled the radiator with coolant with the bleed valve on the radiator off. My car has started to overheat again, and I think it's because I have air pockets. How can I bleed out all the air with coolant already in the system? Is it a matter of doing what someone has just described recently in another post, or is there something more? Quote Link to comment Share on other sites More sharing options...
Wayne Boncyk Posted September 15, 2004 Share Posted September 15, 2004 Actually, the trick of filling the block from a disconnected upper hose (I think that's the one you are referring to) is the best way to minimize air pockets. Make sure you park the car on a slight upslope (with the radiator on the high end) and you should be fine. If the car still overheats after you're sure you've eliminated all the air pockets, it is an almost sure bet that you have a headgasket failure -- especially if yours is a 96-98 vintage 2.5L engine. Quote Link to comment Share on other sites More sharing options...
sunflow99 Posted September 15, 2004 Author Share Posted September 15, 2004 Thanks Wayne, I have been doing everything in the world to make sure it's not a headgasket. I thought I had won when I changed the thermostat, and found the one the repair shop had put in was upside down and smaller than the OEM Subaru. Bleeding is my last hope. Quote Link to comment Share on other sites More sharing options...
Wayne Boncyk Posted September 16, 2004 Share Posted September 16, 2004 Well, I hope in your case that it is just an air pocket -- I was not so lucky. I went thru exactly the same process as you, and during the course of my "experimentation" with new thermostats and the like, the radiator core actually got too hot from the steam pouring out of the block (hot combstion gases really make some superheated steam!!), that I blew a seam on the upper radiator manifold. So new thermostat, new radiator, several fills of new coolant, etc., was all to no avail. But I don't want to scare you now.... Seriously, good luck. If you do find that it is a blown HG (and the most common failure point does NOT result in something that you can observe as a change in cylinder compression, so ultimately you'll have to pull the heads to know for sure), at least these heads are really easy to service. If you're up to the task, you can do the replcement yourself with the engine left in the car. Wayne Thanks Wayne, I have been doing everything in the world to make sure it's not a headgasket. I thought I had won when I changed the thermostat, and found the one the repair shop had put in was upside down and smaller than the OEM Subaru. Bleeding is my last hope. Quote Link to comment Share on other sites More sharing options...
Setright Posted September 16, 2004 Share Posted September 16, 2004 Thermostat facing the wrong way will overheat the engine for sure. Get a genuine one and mount it correctly. Fill from the top hose until it spills over, then fill into the rad. Idle for a little while, shut off, top off the coolant. Run til operating temp, let cool overnight, top off again. Cross fingers. Quote Link to comment Share on other sites More sharing options...
sunflow99 Posted September 16, 2004 Author Share Posted September 16, 2004 I tried bleeding today, but did not get much coolant in the upper hose when it started to overflow. I let it idle, with both the bleed valve and rad cap off, not much movement either place. The level was pretty constant on the rad cap side. So then I capped the bleed valve, started it up again, and had some coolant sorta blurp out of the rad cap, is that the burp? After that the level was still pretty good, so I capped it, and drove, no problems...yet. One other thing I noticed last night was after it started to overheat, I checked the overflow reservior, and it was pretty full. I came back this morning, it was still at the same level. Can that happen because of an air pocket? I've heard that is a sure sign of bad HG, but I'm just trying to save my sanity. Sorry if these questions seem juvenile or have been answered before, I'm a newbie. Quote Link to comment Share on other sites More sharing options...
sasquatch Posted September 16, 2004 Share Posted September 16, 2004 keep at it and have patience....it is a real PITA to bleed them right....you'll find pretty much everyone here has had to do it.. Quote Link to comment Share on other sites More sharing options...
Setright Posted September 16, 2004 Share Posted September 16, 2004 Sunflow, yes a blown HG will make the level rise in the expansion tank. When it actually overheats, it will flow out of the top. BUT, once you stop the engine and let it cool...SLURP! and the coolant level suddenly drops. But nothing is definite yet. An air bubble trapped inside the engine will expand considerably and push coolant into the expansion tank too. What kind of coolant are you using, and how old is it? Quote Link to comment Share on other sites More sharing options...
sunflow99 Posted September 16, 2004 Author Share Posted September 16, 2004 I am using a 50/50 mix of coolant I got at Advance Auto(I know it's probably not the best, but it was there and I needed something cheap at the time.) It's brand new. Quote Link to comment Share on other sites More sharing options...
Setright Posted September 16, 2004 Share Posted September 16, 2004 Okay. Should have a boiling point of around 108 degrees Celcius. Sometimes old fluid will boil "early". You should be okay there. Quote Link to comment Share on other sites More sharing options...
sunflow99 Posted September 17, 2004 Author Share Posted September 17, 2004 Update: I did all the bleeding and "burping" today as per instructions. Tonight, I drove it into DC from Alexandria, about a 7 mile one way trip. Was in stop and go, and no overheats. Coming back, same. So, if it were a headgasket, would it be overheating all the time? If it comes back(the overheating, that is), what can I think then? Thanks for all your help, maybe they should make a new forum called "Subaru Cooling questions", seems like there are enough scenarios out there to warrant it's own space. Quote Link to comment Share on other sites More sharing options...
sunflow99 Posted September 17, 2004 Author Share Posted September 17, 2004 PS just for information, I have a 95 legacy wagon, 2.2L engine(don't know the model). Quote Link to comment Share on other sites More sharing options...
Setright Posted September 17, 2004 Share Posted September 17, 2004 A small headgasket leak will produce overheating, at long random intervals. Most often after long high speed trips. Intervals get shorter, as the leak gets worse. If you experience another overheating scenario, check for an overflowed expansion tank. This will mean a 95% chance of a blown HG :-( However, if you keep the coolant level up, and keep a watchful eye on the temperature gauge, you can drive for months while you save up for the repair! I did. An mine was the legendary EJ22 - so it can happen, but let's assume your car is okay! Quote Link to comment Share on other sites More sharing options...
sunflow99 Posted September 17, 2004 Author Share Posted September 17, 2004 The last time it did overheat, the overflow was fuller than normal, but not overflowing. I checked it this morning(after doing the bleed and burp yesterday and driving it around 15-16 miles), and the overflow was actually a little low, as was described in the bleeding post. So I don't know. Your scenario of overheating after long trips happens to me sometimes, and sometimes not. My question is, why sometimes does it overheat, and not other times if a HG leak is always there? Quote Link to comment Share on other sites More sharing options...
Setright Posted September 18, 2004 Share Posted September 18, 2004 Because the leak is tiny. A very small amount of compression and exhaust gas is slipping into the coolant. This will form a little bubble. If you're lucky this bubble will find its own way out of the system via the rad cap and expansion tank. An a longer trip, or during hard driving, more gases are forced through the leak. When you are unlucky, the little bubbles keep circulating around with the coolant. They like to collect around the water pump, because the pressure drop makes them expand. Once enough of them get stuck in the water pump, you lose circulation and the engine overheats. The increase in temperature makes the gas pocket in the water pump expand and that forces coolant out through the top radiator hose and past the rad cap into the expansion tank. The thermostat will often be closed, because it's sat in a gas bubble, which can't provide the heat to open it. If the system is bled, and there are no external leaks, then the headgasket is likely to blame. A worn water pump won't cause such sudden overheating. And since your thermostat is new, thats not causing it. A bad radiator cap, one where the spring is too weak after years of service could also produce these symptoms, so it might be worth going that way first. You could consider getting a cap with a slightly higher pressure rating. I think 0.9 Bar is standard on your engine, newer Subes use 1.1 Bar. Try one of those, but make sure your coolant hoses are up to it. (1 Bar = 14.5 PSI) Even if your cap is okay, a higher pressure would delay the problem :-) Quote Link to comment Share on other sites More sharing options...
sunflow99 Posted September 18, 2004 Author Share Posted September 18, 2004 Thanks Setright for all your help. Let me ask this, can those air bubbles around the water pump cause the fins of the pump to corrode or melt prematurely? The reason I ask is when I got the water pump, radiator, t-stat changed about a month ago, most of the fins were completely eaten away. I had gotten that water pump from a Subaru dealership in Jan of '02, which means it only lasted about 2 and 1/2 years. Is that the usual life of a water pump, or could air around it keep coolant from getting to it, and it getting too hot and melting the fins? Thanks. Quote Link to comment Share on other sites More sharing options...
Setright Posted September 19, 2004 Share Posted September 19, 2004 Melting the fins? I would not think so. The air might cause "cavitation" in the water pump. That's when the fins spin easily in the air bubbles, but are shocked to suddenly hit coolant, which usually results in pitting of the fin surface. It would take a lot of cavitation to eat up an entire fin. Did you see the pump in Jan 02? Was it brand new? Was it a genuine part? I would expect it to last 120k miles, or ten years. Maybe, hydrocarbons in the coolant, from an HG leak would cause it to corrode. Maybe. Why did you replace the pump? Quote Link to comment Share on other sites More sharing options...
sunflow99 Posted September 19, 2004 Author Share Posted September 19, 2004 I did not see the pump in '02, so I don't know if it was new or not. It was at the Sub dealership, so I hope it was a genuine new part. When I took it in to the shop last month, they replaced the radiator, and it was still overheating, so they pulled the water pump, and saw what it looked like(they gave it to me to keep.) Which leads me to my next question: I am coming to the definitive conclusion that my HG is going bad, so is driving around with a bad HG going to hurt other parts(possibly like the water pump or anything else?), or can I drive it until it just won't stop overheating, as sometimes it's fine to drive right now. Quote Link to comment Share on other sites More sharing options...
Setright Posted September 19, 2004 Share Posted September 19, 2004 Drive it. Keep a watchful eye on the temp gauge. Especially when coming off a highway. AS SOON as the needle moves upward, shut the engine off. Don't run it hot. Regularly check the level of coolant in the radiator - when cold of course - and top it off. Try the high pressure cap. No, unless you let it overheat and keep driving, no other parts will be damaged. Quote Link to comment Share on other sites More sharing options...
sunflow99 Posted September 19, 2004 Author Share Posted September 19, 2004 My eyes can't move off that gauge now as it is. I saw some bubbles in the reserve tank today, so I think in order to set my mind at ease, I'm going to have the HG work done. Thanks for all the replies and help. Quote Link to comment Share on other sites More sharing options...
Setright Posted September 20, 2004 Share Posted September 20, 2004 You are most welcome! Sharing experiences on this board can help save us a lot of time and frustations. Quote Link to comment Share on other sites More sharing options...
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