2002 WRX Overheating

[Rottenpucker]

About six weeks ago, while sitting at a stop light, I noticed my 2002 WRX was steaming a little under the driver's side hood near the front. It wasn't overheating but there was a slow simmer of steam coming out. Then, about a week ago, the car started overheating up to -but not over- the red zone and would then cool back down to a semi-normal level. My first thought was a sticky thermostat so I changed it with no change. Here's what I noticed while looking around changing the thermostat:
1. There was a small amount coolant on top of the radiator and various places around the radiator but not a LOT.
2. The coolant level wasn't abnormal.
3. The coolant looked good, not bad or dirty.

Ideas?

[xsnapshot]

Have you checked both coolant tanks? A thermostat probably wouldn't be causing you to smoke. Does your overflow reservoir have a leak thats dripping onto the exhaust manifold by chance?

I have had the same thing happen to me twice. Both times i had low coolant in the upper coolant tank, and filling it up solved my problems.

[Rottenpucker]

Both reservoirs? I didn't know there was more than the one on top of the engine. I've topped it off and filled the overflow tank to half way. The exhaust manifold and other various areas around where coolant spilled out during the thermostat change do show corrosion. The exhaust manifold shows corrosion as though the thermostat housing is.

So, should I have a flush and fill and go from there??

[SD_GR]

Sounds like a failed top radiator seam. Very common. If so, replace the rad, and take the opportunity to replace the hoses and clamps if in doubt at all.

[Rottenpucker]

Okay, so basically I should take it to a garage and have someone diagnose whether it's a failing radiator or water pump? (I'm assuming that I can do a radiator myself where as the water pump would be beyond my abilities.)

[SD_GR]

A failing water pump is unlikely to generate coolant on the top of the radiator.

Since you changed the thermostat you already know the pump works; you checked for circulation when topping off the coolant anyway. Whether the pump is leaking is of course another matter, but you should know whether you have circulation and/or an obstruction at this stage.

You can have the system pressure tested though.

[Rottenpucker]

Solid point regarding the water pump. I'll take it to the subie guy in town and have him do a pressure check to verify the radiator. Thanks for the advice. I'll post more as I learn more.

[SD_GR]

OK great. If the pressure test does not show any pressure drop, try wiggling the top hose near its attachment to the radiator. Sometimes the leak only shows up when the motor is running, or in any case when there is movement of the radiator relative to the motor, or vice-versa. From what you've said though it does sound like a radiator.

[Rottenpucker]

I took the car to work this morning (limping and hot the whole way) and tightened up the thermostat housing and lower radiator hose clamps. Then I very patiently burped the system and filled the reservoir. After that I ran the car for 20-30 minutes in the bay with the a/c on and the temp never went above normal. (Actually, it was on the low side of normal.) I went and took a shower and came back to the car and found coolant around the top seal of the radiator and fresh coolant splashed up on the front of the engine block. I took photos and have included them here.

[SD_GR]

OK, well, prefaced by "I am not there" here's what I think. It's one of:

1. Burst top radiator seam. Replace radiator. If need be replace hoses and clamps while it's all apart.
2. Leaking overflow return hose. Replace. It should not need a clamp, it's not part of the pressurized loop in the system, but if there's a pinhole it will leak juice.
3. Failed top radiator hose. A puncture or even more rarely a failure where the clamp fits onto the hose. The latter had a TSB issued many years ago. Replace hose. This may lead to replacing the rad anyway, if the fitting is faulty and/or if the fitting simply shatters when the hose is removed or the replacement hose tightened.