Help, No heat at idle. (Subaru WRX)

For most of this (brutal) winter here in SE MI, I've had an issue with my WRX and its heat. For the record, it's a 2002 mostly stock 5spd wagon with 178k and a filter, tune and turbo back for mods.

After it heats up, the car blows ice cold air when sitting at idle. As soon as the car reaches speed again, it starts pumping heat back into the car and all is fine. On rare occasions, mostly if I'm stuck in real bad traffic, the temp gauge will start to climb pretty high but won't get into the "red" part. On some other rare occasions, I'll notice the heat stay on at idle.

I haven't done a real thorough investigation, but I don't notice the car leaving any coolant leaks. The radiator also looked brand new when I bought the car some 20 months ago. I don't ever notice a coolant smell, and there doesn't seem to be any coolant smoke coming from the exhaust, which is clearly visible since the car has a 3" straight pipe... The car also performs like usual.

Last month, I noticed that there was a small bit of coolant on top of the tank infront of the turbo. Knowing that they are notorious for failure, I replaced the tank with one of those snazzy units from Moroso, which comes with a new radiator cap. The tank replacement caused the car to lose a small bit of coolant, but it took a good ammount when I topped off and burped the system. I also remember looking in the overflow bottle and not seeing any bubbling, which is apparently a good sign of an internal head gasket leak.

The issue seemed to go away for a little while after doing that, but I started not getting heat again and this morning is the first time I've seen the gauge climb since then. I've changed my oil atleast two times since this started happening and there has not been any coolant in the oil.

I've heard all sorts of possible culprits ranging from cheap and easy fixes like a T-stat stuck closed/open, clogged heater core, or an air bubble/low coolant. However, I've also heard it could be a bad headgasket or even a cracked or warped head.

Does anyone maybe have a similar experience, or can someone maybe rule out some of the possible culprits?

I have a brand new OEM t-stat and a good supply of the Subaru coolant, and I was going to try putting in the t-stat tonight. Anyone thing I'd be wasting my time?

Thanks.

You have all the classic signs of being low on coolant. Have you checked your levels when you stop getting heat?

If your thermostat was stuck open you'd have overcooling problems in the winter, definitely not temps climbing above optimal...

mad_machine wrote: You have all the classic signs of being low on coolant. Have you checked your levels when you stop getting heat?

I haven't checked the level since I changed the tank. I'm suspecting it might be low, but not sure how it got low (again?).

shelbyz wrote: However, I've also heard it could be a bad headgasket or even a cracked or warped head.

FIRST check your coolant levels, then if you are worried about the head, peek under the valve cover. I doubt you'll find anything more than oil under thurr.

If you bring the revs up at a stop will it start behaving?

Have you ever changed the timing belt? If so what water pump did you use? I suspect something is up with the water pump, like the impeller has disintegrated too much or is spinning on the shaft.

Kenny_McCormic wrote: If you bring the revs up at a stop will it start behaving? Have you ever changed the timing belt? If so what water pump did you use? I suspect something is up with the water pump, like the impeller has disintegrated too much or is spinning on the shaft.

Haven't really tried revving it to see what's going on. Usually, the heat will abruptly kick back on when the car starts moving.

I've never changed the timing belt/water pump/etc. I bought the car with 146k and it was a one owner dealer maintained example and I figured all of that had been done at the recommended 100k interval. I figured I'd do it when it started closing in on 200k, or if I needed to pull the motor for anything.

With respect to timing belts and related components, I always assume without strong evidence somebody has been in there(receipts or running a not OEM belt) that its all original.

what mad_machine said … that is exactly how my Suby (Impreza not WRX fwiw) acted … topped off the fluid, and everything was good again

I know you said air pocket, but Im thinking air pocket... had same issue in an old Maxima.

This is how my WRX used to act when it got low on coolant one winter. Since you had a crack that leaked coolant.. that's again where I'd look first. Check the level lines on the expansion tank after the car's been sitting for a few hours, then fill there.

Also keep an eye on the plastic radiator endtanks as I've heard of way more of those failing (albeit, not often with a pinhole leak) than the upper coolant reservoir.

Subaru dealership should be able to tell you whether or not the WP/TB has been done correctly, as well as all other services (there's a TSB out right now for control arm corrosion).

I played with it a bit tonight after work, so here's an update.

Car was slightly still hot, reservoir had some real awful looking crap at the low fill level. Topped that off and burped the system at the expansion tank or whatever it's called. Some air bubbled out, but it didn't take that much coolant.

The one thing that I noticed, was that the fans never once came on at idle while I was burping the system. I gave it some gas and it took down some more coolant from the fill funnel thing. Flipped on the A/C button and only the passenger fan came on. Checked the fuse panel and the main fan relay was absent, while there was a relay sitting where there isn't supposed to be one. Switched them and the other fan came on. Turned off the A/C button and let it idle a bit longer, but the fans still never came on. All while doing this, the needle never moved from its normal spot.

After squeezing hoses and such, it didn't seem to be taking any more coolant. I took the car out, driving it pretty liberally. Heat stayed at idle, and the temp gauge didn't move. I stopped at a couple places, each time giving it some idle time to idle and still no fans.

Parked it in the garage when I got home and again gave it some time to idle, still no fans. Shut it down and looked around under the hood. The coolant in the reservoir was ice cold, and so was the lower hose.

I'm stumped?

shelbyz wrote: Heat stayed at idle, and the temp gauge didn't move. I stopped at a couple places, each time giving it some idle time to idle and still no fans. Parked it in the garage when I got home and again gave it some time to idle, still no fans. Shut it down and looked around under the hood. The coolant in the reservoir was ice cold, and so was the lower hose. I'm stumped?

What are you stumped about? Coolant was low, you topped it up, and the heater now works. The engine never got over 200 degrees so the fans don't need to come on, the reservoir and lower hose contain cold coolant, just like they are supposed to. Sounds like you need to keep an eye on the coolant level, and watch for seepage.