legacycentral bbs

ok, here's the story:
Waaay back in like march or something my subie, almost home from a short in town trip suddeny spiked on temp. I was already pulling in the drive at home so let it sit to cool off and topped of the coolant. no leaks found, didn't take hardly any fluid to fill it back up. no more overheating dispite basic daily driving and even a few short jaunts on the freeway.

That is untill late friday night. I was coming home from the local haunted attraction, hwy, speed 55, nothing special. probably 10 to 12 miles from where I'd started when, without warning the check engine came on and the temp gauge was thru the roof.
I pulled into a gas station that was right there, used the restroom, got some coffee, returned to he car to see how the cooling down was going. (all total maybe 10 min max)

No puddle, no steam, hardly any coolant was needed, and the radiator and cap were cool to the touch. I thought this odd and turned her on to see what the gauge said. PERFECT normal temp, not even the slightest bit high.
She couldn't have cooled down that much that quickly.

Like in the spring she has been driven with no signs of any issue since.

I'm wondering if maybe this is a bad sensor or something. I've not pulled the code, mostly because I'm not sure how (its my first subbie) and if it matters or not I've been fooling with a bad idle for a while, changed to IAC improved, but not right, and got a good used throttle body (not yet installed)

So anybody got a clue? some sensor? or what? ever had a similar problem? its really infrequent so how will I know if its fixed?

What code was in the ECU?

If the radiator & cap were cool to the touch, you've probably got a stuck air pocket, or possibly plugged radiator (less likely, but I wouldn't rule it out....since something funky is going on.

Yeah, it doesn't sound like a bad sensor because a CEL came on AND the temperature gauge read hot. They both use different sensors, so it would be unlikely that they would both report that something wasn't right.

I'm with Josh on this one, sounds like an air pocket or maybe you have a thermostat that's going bad and occasionally sticking closed. That's what mine did when it started to go bad, except it was staying open when it shouldn't have.

Could be an air pocket.

You say you added coolant twice though? And found no leaks?

I know blown head gaskets don't cause infrequent overheating, but where is that coolant going?

I might side with ASC on this one, it sounds like every now and then something is clogging, or keeping the anitfreeze from flowing.

I'd first off smell your coolant, see if it smells like exhaust.

And make sure you test things before you start replacing parts, you don't need to waste money "uhh!"

And next time you're over heating turn your heater up to full blast, and hottest setting.
You might know that, but it'll cool your coolant dramtically.

I'm not sure if your USDM models are set up the same way, but I had a weird problem some years ago with my 2.2 NA wagon. I had the radiator re-cored, and had a new thermostat fitted at the same time. There hadn't been any overheating problems, but many of the cooling fins on the core had disappeared so this was purely precautionary.

Two weeks later I was coming home down a hill on a cool evening minding my own business when i noticed the temp guage reaching for the sky. I stopped immediately & popped the hood, expecting to see steam pouring out. There was none. No water leaks, no sign of excessive heat, nothing. Then I noticed that one end of the radiator was hot while the other end was cold, and thought maybe that the new thermostat was faulty. After a few minutes on the side of the road, i drove home with the temp back to normal and parked it. I checked with the mechanic who'd changed the thermostat next day, and he pulled it out and replaced it, even though it checked out OK when he tested it.

It then happened again a few days later.

This time, we asked a local Subaru dismantler for suggestions, and he said, "it's a blocked heater core. Bypass it and your problems will be over". We fitted a bypass hose which still left the heater in the circuit but allowed coolant to flow around it as well. No further problems for the next 60,000mi until it got written off earlier this year. No overheats, no loss of coolant at all.

The reason we were given is that the heater core outlet re-enters the thermostat housing. If the heater core is blocked, the coolant takes so long to pass through that it's cold when it hits the thermostat, fooling the thermostat into closing and thus causing the temp spike. If the cooling system has been serviced, often the sediment in the system gets disturbed and can block the fine tubes in the heater core.

I spoke to the radiator guy a few days after this happened, and he said, "wow, you wouldn't believe the number of Subaru's I've done re-cores for, that have seized mysteriously a few weeks later!"

okay, so possible air pocket. I'll start there. a stuck thermostat just seems like it would have left things hotter. (has on other rigs in the past)

I didn't add much either time, like the overflow resivoir was half way between full and min.
heater was on, this last time at least.

the code I'll have to look up how to pull that. think I seen it around here somewhere.

still no more symptoms. shoot, its a $500 car with 274k. gotta expect a little issue every once in a while, but she runs great normally


the other replaced parts were for the seemingly unrelated idle and it's improved. only mentioned because somebody ,on a list of guesses for that problem ,had mentioned a coolant temp sensor WAAY at the bottom of their list.

My Subaru has done this to me twice.

The first time, I didn't notice until it had peaked, and was coming down, and this morning on the way home from work, it did it. There was no CEL, or any other indicator light, either time. Last week I was enjoying some rather aggressive driving and it never had a temp spike like it did this morning.

Anyway, I pulled over and put the heater(bilevel for more air flow) on the highest setting, but it started to blow cold(ambient 40-ish) air! So, if it is the case as described by Max, up above, then I think running the heater might not be a good thing to do, and if it happens again, I see about turning the heater off.

I just checked the service records, and I see that a new radiator was put in, in June, so I'm starting to think it might be that the heater core has become plugged.

If I do go with changing out the heater core, how involved is that job? And if I'm gonna pull the dash what else should I consider while it's all accessible?

Do I really need to mess with the airbag? I get kind of nervous messing with stuff that is designed to blow up in my face...

SC

Yes, you have to pull the dash to get at the heater core...

I know that much...