Topic: 2.5 overheat, rad cold....??

[shauno]

Okay so the basics....98 legacy sedan with 2.5.

The car runs pretty well, no CEL or anything lots of get up and go, but after driving for 5 min at "normal" temp the needle just spikes.

The top rad hose is smokin hot, the rad is cold, the fans are running, the rad cap is cold (with lots of pressure if you loosen it) The lower  rad hose is cold, the thermostat is cold....but the water pump is hot. I think the water pump was replaced when the newer motor went in as its not as dirty on the block and there was an old ugly water pump in a box in the car when I got it.

I've flushed the coolant, twice now. Replaced the thermostat and have burped it repeatedly on ramps. I can't open the bleeder valve on the rad on the passenger side as its stripped out.

I'm trying to figure out where to go from here. New Radiator? New water pump? Drill out the bleeder valve and find a bolt to replace it with?

Head gasket issues keep flashing through my mind, but there doesn't appear to be any oil in the coolant, and the oil in the engine looks clean from a recent oil change (the old stuff was BLACK when it came out). Besides, how would a head gasket cause a cold Radiator?

Help please. This is my first subaru, was supposed to be a cheap winter car but is getting more and more expensive!!

I've searched and searched, lots of similar problems, but no one ever follows up with the solution that worked.

[Zaider]

Hmmm. It sounds like you dont have either a functioning water pump or a functioning thermostat.

The fact that your upper rad hose is hot and the rad is cold means that coolant isn't flowing through the system. Its not an air-in-the-system kind of thing.. that wouldn't stop it from cycling.

[shauno]

Ok, so I went and played with it a bit more, had it up on ramps and then jacked the drivers side up as far as I could to try and burp it some more. THIS time I left the heater in the car off.

Air bubbled out and I think it helped as the rad heated up and so did everything else.

I let it cool, topped it up as needed and then fired it back up to burp it one last time. Rad heated up, lower hose heated all is good. I let it idle with the cap off for 20 min at temp. Fans kicked it and rad level dropped a bit. It was bubbling a bit this time but eventually sort of stopped and just slowly leaked from the open cap as it heated.

Put the rad cap on and went for a drive, still had heat in off. Drove about 10km, hard, and easy and temp stayed perfect. SO, I turned on the heat to full blast and within about 3km she overheated. I pulled over and found the rad to be cold, lower hose cold but top rad hose was HOT.

Turned the heat off, let the car cool for about 5 min with the hood open, fans going, and a cold wind blowing right in. Started it up, heat off now, drove up a big hill and all the way home with no issues.

WTF is going on?

Car seems to be ok till I turn on the heat!

Sounds to me like when I turn on the heat full blast I am taking too much heat out of the system and the return line to the thermostat/water pump from the heater core isn't warm enough to keep the thermostat open??

I have a NAPA thermostat in there. Should I buy a subaru one? i can't imagine there is much difference. This is ridiculous.

[bejamin]

Sounds like the thermostat isn't cycling in the right temperature range. It certainly is a strange symptom.

[Zaider]

What about a broken  heater core? Im just spitballin' here... but if that seems to trigger the problem, maybe when the heater is on, it is not letting the coolant cycle...

[lophilip]

Maybe the heatercore is hooked up backwards? I'm grasping at straws.

[shauno]

hmm heater core up backwards....good thought. I'll check that out.

In the meantime I went and bought a subaru thermostat. I looked identical to the one I took out to begin with and almost identical to the NAPA one. So i decided to modify it a bit. I took out that little metal stopper piece and used a 1/4" drill bit and drilled the hole bigger.

Installed that into the car and voila. No more problems with overheating. BUT, now its about +3 celsius outside and when I cruise at highway speeds the temp drops to about half way between cold and middle. When I stop and idle it comes up to temp, whether it be a traffic light or just warming it up to begin with.

SO maybe the hole was a little big at 1/4". At least I can drive the car now, I will look into this further.

Appreciate the ideas.

[bejamin]

I have changed the water pump and thermostat a lot of time on different turbo charged Subaru's, i have never had a problem with that little nipple.

This might sound stupid because i know on turbo Subaru's you can't install the thermostat backwards but are you sure you didn't install it backwards. Just wondering. 

[shauno]

 thermostat is in the right way. I tried it "backwards" and it didn't fit, so I know its in right.

[Cbxj]

Ive had 2 2.5's (2.5 dbl oh cam) that the head gasket(s) went south.
Here is the story.
1St time.. long drive down to Great Falls and Back... everything working just fine.. stop in Lethbridge, Start the car an hour later ,and the temp spikes,,, wait an hour ... same thing.. so I'm thinking stuck Thermostat or water pump fail. So drop the coolant out of the thermostat housing.. and the stat is covered in black gunk and kinka sticky...OK, drive back to calgary with no stat and water in the cooling system..no problem. At this point I also notice my overflow tank has some black gunk in it, but there is no loss of oil or coolant. Change the stat (cdn tire) new AF, all is well ... for about 6 weeks of driving around.. then another temp spike (after driving a short distance). AGAIN stat is "clogged" and sticky, so I think dummy me for going to cdn tire, buy subaru stat and af..... and that lasts about six more weeks.. Then I stop being lazy and do a leak down test--- blown head gasket drivers side.
2nd time. (different 2.5 dbl o/h cam).. Same thing, execpt now I watch for black stuff in the overflow tank, and know right away at the first temp spike, toss my stat on the garbage, put in water, and start planning to pull the engine and do the head gskts.
Funny thing is BOTH happened right around the 265,000 KM mark (like within a few thousand). My white OB now has close to 400,000 and no troubles since.
I think some of your troubles have a simillar theme...?
OH and, when I was driving around with the 2nd one, prior to pulling the stat, there seems to be some type of pressure thing going on with the stat, as it would not open (even thou it was not all that "gunked up") ... it seemed that as the car warmed up it pressure loaded the stat so it could not open ...JUST My GUESS.