Once again, my 1990 Legacy Wagon is having an issue. It overheats after about 15 minutes of driving. The coolant level hasn't gone down in several days. This started when my radiator house blew, i replaced the hose and still nothing, next was the thermostat, nothing. Perhaps the water pump? There are no wet marks under the vehicle when I leave it sitting so I'm assuming no leaks. Help?

Radiator hose blew* not Radiator house. Lol

What brand of thermostat did you use? If it wasnt Subaru that's probably the problem.

So you weren't having this problem until after the hose blew roght?

You may have already tried this but turn your heater on when it starts to over heat. I have seen this happen a million times after a hose, thermostat, radiator etc gets replaced. What happens is you get air bubbles in the system and so air gets trapped on top of the thermostat and the coolant  doesn't engage the tstat thus causing overheating. Also when you fill your radiator (from the radiator cap, not the overflow) make sure you unscrew the plastic plug on the top left of the radiator. This allows for filling up the radiatar to the fullest because it allows air to escape. This plug is has either a square head or a phillips head. After the air bubbles escape make sure to check the fluids again cause the level can drop. I drive a 90 wagon and this happens nearly everytime I replace something in the cooling system. It happened 2 weeks ago after replacing the tstat, but turning the heater on for a couple seconds did the trick.

Also check the function of your fans - are they working? but yeah - kind of sounds like trapped air in the system...

Probably air in the system, are you using the vent plug when your filling it? Also you need to fill it slowly to get all the air out.

I had a stuck thermostat; when replaced the problem went away. 

Exercise proper coolant fill procedire. Full the block by the upper hose first.

 

Run the heat as if the coolant level is too low, the heat will go cold. Lets say if you had a leak, running the heat is a good way to know when to top off when it goes cold. Even if you have to run the heat in the summer. good luck.

Update: Will everybody just call me an idiot please! I forgot to fill my radiator back up after I changed the tstat. I just filled the overflow. Dumb me. Now that I've done that. Everything seems ok, except the car still runs very hot. It won't go into the red area but it will get close. I've noticed that now after turning my car off and letting it sit a minute the overflow resorvoir will suck back into the radiator until empty. It's done this twice today. No leaks that I can see. Help?

Another update: I have the dreaded bubble effect. Bubbles are surfacing out of my radiator when the cap is off and the engine is running. Head Gasket? :/ there's no white smoke and the oil is ok.

You are putting the cart before the horse here  - it could simply be trapped air still in the system coming out - is it still sucking the overflow bottle dry? if it is, then it wasnt filled enough/properly and is still trying to burp itself. the still running to the hot side suggests this as well.

 

Have you turned on the heat to circulate the coolant thru that part of the system yet? If not, you should.

 

I would keep an eye on it for a week or two, dont go jumping to conclusions after just a couple of hours.

 

If you are still getting bubbles after a week or so, then you can entertain thoughts of headgaskets.

So I've let it sit, Burped it, and let it sit again. Still overheats after driving 5 or so miles. As I was burping the engine, a lot of air came out. I then turned the car off after I knew all the air was out, and the radiator sucked the overflow tank completely dry, the upper rad hose got all squished together like when you take a straw, put your finger in one end and suck all the air out of the other. Weird??? I can tell when the thermostat opens and closes, but the coolant reduction is very small. Oil checks out ok So I'm not thinking its a HG. I'm gonna pull the Tstat today and see if it runs fine without it, then that kinda boils it down (no pun intended) to HG or T-Stat. Anyone have any other ideas on what this could be?

Edited June 29, 201312 yr by ThatSubaruKid

There's still air in the system. That's what causes the overflow to suck dry. The system is not full and it is pulling vacuum as it cools. This pulls in the extra coolant in the overflow tank and will suck the upper radiator hose flat.

 

An empty system holds 1.6 gallons of coolant. If you didn't pour in at least 1.5 the system is nowhere near full yet.

 

When filling the system you need to fill the engine through the upper radiator hose Before filling the radiator, otherwise it will take several cycles of running to temp, and cooling and refilling to get the system completely full.

Just pull the hose off and run the water through the hose into the radiator or the other way around?

Ohhhh I think I understand now.

just for clarification purposes - pull upper radiator hose off the radiator, leaving it attached to the engine, then pour coolant into the engine block thru the hose.

 

Got it? Good! now go fill your cooling system!

And to burp it should I just drive around with the radiator cap off or what?

Don't drive the car without a radiator cap, it'll just spill coolant all around the block.

Top off the radiator then let it idle in the driveway until it reaches operating temp with the cap off. If coolant starts to push up out of the radiator put the cap on it and let it warm to operating temp. Fill the overflow to the MAX line cap the radiator then turn the engine off and let it cool.

Repeat until the level in the overflow bottle stays the same after cooling. This method can take quite some time, which is why I recommend loosening the upper radiator hose and filling the engine up first.

Matbe running it low on coolant cause the HG to fail and now you have bubbles. Do they smell like exhaust> Is there an oily film in the radiator cap? The engine can tolerate a mild over heat once, but repeatedly, you may as well count on doing the HG's

I've bled the Cooling system several times now. I can drive all around town now just fine. I drove around town about 20 minutes today and I was okay, but as soon as I get on it to get to highway speeds, the temperature increases. Maybe it's because I didn't use a "Genuine" Subaru T-Stat???

 

What brand of thermostat did you use? If it wasnt Subaru that's probably the problem.

Third post.

Damn....

either Subaru brand, or the Stant Exac-stat - part number 48457 - anything else is a waste of money.

You MUST only use a Subaru OE t-stat or the Stant Exac-stat - part number 48457. If you use whatever they have at the parts store then you will have issues.