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View Full Version : Weird overheating issue!



Scimitar
10-18-2010, 11:24 AM
Morning all,
First off, I'd like to say just how awesome this site is. I've been lurking around here for the past few months, and the knowledge gained is overwhelming. Definitely one of the most addictive sites I've been to in a long while.

Now here's my dilemma...
I've been searching around for solutions to overheating problems, and I'm not 100% sure what's causing mine
Car is a '98 2.5 GT with just under 133,000 miles. Well maintained, regularly serviced and such. I take good care of my cars, except for the occasional 4-5K RPM shift :wink:

*Warning! Wall of text ahead!*

Last Tuesday, while driving home after being on the road for about 45 minutes or so, my A/C quits blowing cold, and I can hear belts squeaking. I knew they needed to be replaced soon, so I figured one of them got thrown. I'm only a half mile from home, so I ride it out. I pull in the driveway, and smell coolant, so I jump back in the car and turn it on (not starting) to read the temp gauge, which is to the hot side, but not pegged (roughly 3/4 of the way up). I let the car cool off for about 30 minutes before driving it to my grandpa's shop, about 100 yards away.

It appears that she'd been blowing coolant out of the overflow tank, which got my old belts wet (along with the rest of the driver's side of the engine bay), hence the squeaking. My grandpa and I determined that the thermostat had somehow stuck shut, and that the water pump was pushing the coolant out because it had nowhere else to go. On Thursday we replaced the thermostat, hoses, and belts, refilled the coolant, and took it for an hour-long test drive. Everything seemed to work fine, and we deemed the car "fixed".

Friday, I drove the car to Lynchburg (roughly 4 hours) with no problems to speak of... temp gauge was normal, and I checked the coolant every time we stopped. Saturday, we drive from Lynchburg to Peaks of Otter (about a half hour away), and not 10 minutes from our destination, the gauge pegs. I pull off the road, and sure enough, it's pushing antifreeze out of the overflow bottle. I always keep a gallon of 50/50 in the trunk, so I let the car cool off, refilled what coolant was lost, and took it easy driving up the mountain (which is NO FUN in a Subaru :-( ). Just as we're about to pull into the visitor center parking lot, the temp starts to creep up again, but as I'm about to park the car, it never got to "H". I make a note to check the coolant again before we leave the parking lot, and we go for our hike.

Well, like a dumba$$, I forgot to check it (hey, if you were as out of shape as I am, you'd probably forget after hiking up and down a rough terrain trail too! :lol: ). Fortunately, despite my moment of forgetfullness, the car behaved itself for the 5 minute drive to Gross Orchard's Apple Fest. Here is where I remembered "Oh yeah! I forgot to check the coolant!" but I guess it didn't lose much the last time, as I only poured a tiny bit into the radiator before it wouldn't take anymore.

So here I'm thinking that maybe I had overfilled it, but on the trip home that afternoon, we had to stop twice for the same issue.

Now, in all the searching around I've done, this problem seems to be pointing to a bad head gasket, but here's where I'm not so sure:
After the last overheat session, I decided to keep the RPM's no higher than 2500, and we never had to stop again for the last 2 hours of the trip. I read a different thread on here about someone using an aftermarket thermostat, and it looked different from the OE version. When I replaced my thermostat, I had the same issue with it looking different. I didn't use an OE part because I get them online, and I didn't have time to wait for shipping (the closest Subaru dealer to me is horrible, and I refuse to do business with them anymore). So now I'm thinking "Hey, is the thermostat too small for the car?". ALSO, when it overheats, there is NO coolant in the upper hose, yet it's hot to the touch...but the driver side of the radiator is cool, like the car had never been started. If you relieve the pressure by partially turning the radiator cap (yeah, I know that's not too smart), the coolant that comes out isn't even warm... could that mean a blockage in the radiator?

I'm pretty lost at the moment, and I don't really want to start tearing the car apart until I have a good idea of what could be wrong.
We've already checked the radiator cap, and done a pressure test on the coolant system; none of them have turned up any problems, but I read today that it doesn't mean a whole heck of a lot if the problem is in fact the head gasket. I guess the next step is a leak-down test?

Apologies for the constant rambling, my brain is just so fried from the last 2 weeks, this definitely isn't helping :smt011

Huffer
10-18-2010, 04:22 PM
Couple of things - if there's no oil in the coolant or foaming bubbles, it's unlikely to be a headgasket.

It sounds to me like you have a blocked radiator or the radiator cap isn't holding pressure or holding too much. It could also be that you have multiple air bubbles in the coolant still.

CoryCopas
10-18-2010, 08:27 PM
I agree with Huffer. It's most likely not gonne be the Headgasket. I personally have noticed that the Thermostats suggested for Subarus aren't very forgiving. I went through four or five before mine worked right. Also, you might want to drain the coolant and refill it again real slowly. Lots of air bubble can cause repeated overheating. Hope the best for you man.

01 gt
10-18-2010, 09:31 PM
Get a OEM thermostat , that how i fixed my problems.

Grafton
10-18-2010, 10:43 PM
+1 oem thermostat the after market ones have weird effects on our cars, if you do flush and refill, take the upper hose off the radiator and use it to slowly fill the block up, it helps to not have trapped air bubbles

Scimitar
10-18-2010, 11:17 PM
Well that's a relief to hear...
I'll definitely get an OE thermostat, I knew going with an aftermarket one was a stupid idea, I just didn't have the time to wait for one to come in :smt021
I'll play around with it a bit tomorrow and see if anything comes up.
Thanks guys!

Kiwi GT
10-19-2010, 05:26 AM
Test the thermostat in a pot of water being brought to the boil, with a thermometer in the water to monitor opening temp. My money is on the thermostat being ok. If it is, your heater core is likely blocked. Not blocked enough to stop flow, just enough to restrict it. It's the heater flow that opens the thermostat.

https://sl-i.net/FORUM/images/imported/2010/10/coolantflowdiagramgif-1.jpg

BG5guy
10-19-2010, 01:07 PM
id also recommend getting your head gaskets checked, anytime you overheat a subaru more then a few timees, specially the 2.5's you run the risk of blowin a gasket and possibly warping your head. just a suggestion even though it probably is your thermo

Scimitar
10-19-2010, 02:07 PM
Okay, I tested the OE thermostat this morning. According to the thermometer I used, it opened right at 182. It says "78*C" on the thermostat, which converts to 172F...but I don't think 10 degrees makes THAT much difference, does it? Before putting the OE one back, my grandpa suggested temporarily running the car without a thermostat to see if there was a restriction anywhere else. I was a bit leery about this, but we tried it, and it doesn't overheat anymore.

We made sure to bleed the air out as best as we could (which is a lot easier without having to wait for the thermostat to open), but upper driver side of the radiator near the cap is still cold, even after getting everything else up to operating temperature. Also, after driving for a few minutes, I'll start to get bubbles in the overflow tank, but if you release pressure at the radiator cap, they don't start again until the car is driven again. I was under the impression that a blown HG would constantly bubble. Could it be that 2.5's are just that much of a pain to get all the air out?

Also, a reputable shop near my house said that they can check to see if the radiator is flowing properly for $20. As easy as it is to pull out of the car, I figure it can't hurt to be completely sure.

*EDIT*
Also, after re-reading Kiwi's post, would the heater core still provide good heat if it were restricted? Because the heater still blows hot...

BG5guy
10-19-2010, 03:03 PM
check for a colapsed hose also

Kiwi GT
10-20-2010, 03:22 AM
On high, it would normally blow hot for a minute or so then go lukewarm.

Matty2Hotty
10-20-2010, 03:29 AM
It should be pretty simple... Therm stat, water pump, colasped hose, take your radiator out and have it flow tested, defective radiator cap, air bubbles in your system & LAST your collant sensor could be crap causing your gauge to read a faulty reading!

ouch1011
10-20-2010, 10:49 PM
Based on the symptoms, I vote blown head gasket. That is exactly how mine, as well as several others I diagnosed have acted. Mine was blowing combustion gas, not oil, into the coolant, causing it to overpressurize and push coolant into the recovery bottle. The higher the engine load, the higher the combustion pressure, the more pressure getting dumped into the coolant, the faster it overflows and overheats. On my car, I could drive around gently for 30 minutes before it started to overflow, or I could floor it and run it up to 60mph and it would start overflowing immediately.

Scimitar
10-21-2010, 12:47 PM
Well, I got the radiator back today. Shop says that it's blocked up pretty good; they tried to flush it out, but no dice. Looks like I have at least part of the problem figured out...

Kiwi GT
10-22-2010, 01:29 AM
If your rad is blocked, then your heater core will be too as the tubes are much smaller.

Matty2Hotty
10-22-2010, 02:42 AM
+1 on the heater core too! Get that guy swapped out too and you should be back on the roads!

Scimitar
10-24-2010, 04:41 PM
Welllllll... it took a few days, but I finally got a new radiator. I put it in this afternoon, made 120% sure that there is no more air in the system, and took it for a test drive. Sure enough, she runs cool as can be!

As far as the heater core goes, they aren't that expensive, but the radiator drained (no pun intended) a lot of what money I had left (lost my job on Oct. 1st, and still looking for another...Unemployment is a joke). BUT, the heater blows just as hot as can be, so I can't imagine that it's stopped up by very much. Even so, the fact that the radiator got clogged up, and knowing now the way coolant flows on these cars, I'll replace it as soon as I can for the peace of mind... unless any of you know a sure-fire way to diagnose it before changing it.

Anyway, I appreciate all the help and opinions. I knew there was a reason this site was awesome! Thanks!

Huffer
10-24-2010, 05:42 PM
Glad to hear the problem was solved!