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Here's the symptoms. Any help with potential diagnoses is much appreciated.

2003 Subaru Outback, 2.5L engine. About 117,000 miles. I've had it in either Utah or upstate New York the whole 9 years I've owned it. Stored in a heated garage for 4 of those years, outside the rest.

Symptom #1: Last night, I was driving to my girlfriend's place, which entails climbing into the foothills of the mountains. As I got there, I noticed that the temp gauge was nearing the red. My coolant level is full. Then all of a sudden for no reason I could figure out, the needle plunged back to where it normally runs.

Symptom #2: On the way home from my girlfriend's house, the heat wouldn't kick out hot air. Normally, as soon as the temp needle starts to move up, you get warm enough air to turn on the heat. This time, nothing. The needle went all the way up to normal operating range, and still nothing. Then all of a sudden, the heat kicks in and the air is warm. But it doesn't stay there. When I came to a stop, back to cold air. Hot air would cut in and out at random.

My best guess is that the problem is with the thermostat that regulates coolant flow, or something along those lines. That would explain why the running temps are all over the place at random, and would explain why the heating core (or whatever it's really called) isn't always getting heat to it. But then again, I know almost enough about stuff like this to get myself in trouble.

What's the part called, and how difficult will it be for a hack like me to replace?
 

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Are you checking the coolant level by removing the radiator cap? It sounds as though the coolant is low and there isn't enough in the engine to push through to the core. Just because there may be coolant in the resevoir does not mean there is sufficient coolant in the radiator and engine.

Now that it has run hot, you need a thermostat. The engine needs to be checked for signs of a coolant leak. If you can't find the leak, replace the radiator cap when you do the thermostat. The thermostat is easy to change.

Be sure to get the thermostat from Subaru. It comes with a seal. Get the cap from Subaru or any parts retailer. Use good coolant and no tap water. Be sure to "burp" the system when you refill it by leaving the cap off the radiator through a few thermostat cycles.
 

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Are you checking the coolant level by removing the radiator cap? It sounds as though the coolant is low and there isn't enough in the engine to push through to the core. Just because there may be coolant in the resevoir does not mean there is sufficient coolant in the radiator and engine.

Now that it has run hot, you need a thermostat. The engine needs to be checked for signs of a coolant leak. If you can't find the leak, replace the radiator cap when you do the thermostat. The thermostat is easy to change.

Be sure to get the thermostat from Subaru. It comes with a seal. Get the cap from Subaru or any parts retailer. Use good coolant and no tap water. Be sure to "burp" the system when you refill it by leaving the cap off the radiator through a few thermostat cycles.
I only checked the coolant level in the reservoir. I didn't pull the radiator cap when I got home last night for obvious reasons.

I've had a minor coolant leak in the past, but it seems to have stopped now. It would leak from somewhere onto the exhaust pipes, sometimes making the interior of my car smell kind of like a maple donut.

-I also have an oil leak, also frequently hitting exhaust pipes under the engine, giving me that pleasant burning oil smell in the car. The burning oil smell is at its worst when I'm climbing steep hills and putting the engine under strain. Forgive my ignorance, but would these be related at all? I asked the dealer mechanic about the oil leak when I had my timing belt replaced recently, and he said it would run about $2,000 to get the oil leak fixed. Is this the head gasket problem that appears to be a very common issue with these cars?
 

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First make sure the valve covers seals are not leaking. 2003 its about that time the valve covers will start leaking oil. Under load ie going up a hill this would match your description.

Coolant you need to pop the cap off when the car is cool and make sure it has coolant in the radiator.

HG issues more often than not are tied to a few things with cars beyond the 2002 gasket design problem. If your car sat parked for long periods of time and you have a very spotty oil change history that will actually cause gasket issues. This would fit the valve cover gasket leak ie oil problem you describe and could contribute to a failed HG involving coolant loss. Just about any brand car will have similar issues when the oil is not maintained and the car is stored for a long period of time etc.
 

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The heater in all cars uses coolant if the heater is not putting out hot air and should be - that means you do not have enough coolant in the system to provide heat via the cabin heater. This means Pull over NOW and put some coolant in the car before you basically destroy the engine.
 

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First make sure the valve covers seals are not leaking. 2003 its about that time the valve covers will start leaking oil. Under load ie going up a hill this would match your description.

Coolant you need to pop the cap off when the car is cool and make sure it has coolant in the radiator.

HG issues more often than not are tied to a few things with cars beyond the 2002 gasket design problem. If your car sat parked for long periods of time and you have a very spotty oil change history that will actually cause gasket issues. This would fit the valve cover gasket leak ie oil problem you describe and could contribute to a failed HG involving coolant loss. Just about any brand car will have similar issues when the oil is not maintained and the car is stored for a long period of time etc.
OK, thanks. It's never sat unused for long periods of time. And the longest I've gone between oil changes is 4,000 miles and I keep an eye on oil levels pretty carefully. But it sounds like the oil leak is getting over my head, so I'll have my guy take a look at it. At least I have an auto mechanic I can trust.

Thanks for your help.
 

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Valve cover gasket replacement should not run you more than $300 at a local LEO shop. Be sure they use the subaru gaskets - a few folks have tried cheaper non brand gaskets and had issues with them not fitting or leaking soon after doing them.

Easy check look at the spark plugs if you see oil in the spark plug hole or on the wires near the engine - this is the classic valve cover gasket leaking. Not a big deal but needs to be done given oil will also foul up the wires and cause shorts with the spark plug and the engine will run rough.
 

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I would bet that when the radiator is filled the leak will reappear.

Check the heater hoses running from the rear of the engine for wear/leaks. They will drip onto the exhaust. Look on top of the engine for puddled coolant that would run down the back of the engine.

If you can't see a leak, it may be a good idea to have it pressure tested.
 

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Discussion Starter #9
You guys nailed it. I re-filled the radiator and it ran like a champ. Everything seems to be in proper working order now.

And I think I found the source of the leak, or at least one of them:


I cleaned it up a little before taking the picture, but there's obviously been a lot of fluid being sprayed out of this hose. So the plan for Saturday morning is to change out the thermostat and the hose running from radiator to engine, and the engine to radiator hose. They've been on there for lots of years now and I've driven it through an awful lot of mud, snow, salt, and sand since it was last changed. I've also since lost the undercarriage splash guard, so that hose has been punished. I figure if I'm going to the effort of changing the thermostat, I might as well do those at the same time. Radiator caps are cheap, so I'll probably replace that too, although I don't think that's the problem. There was no evidence of leakage out of the top of the radiator.

While I was under there, I noticed that it looks like I've lost a chunk of metal from the base of the exhaust exit:


Is that anything I need to be concerned with?

Last, I took pictures of the spark plug areas because they appear to be squeaky clean. So does that mean the oil leak is unlikely to be related to the valve cover gaskets?
 

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Yes only use a stock Subaru thermostat the cheap junk you buy at the local parts store will cause your subaru to over heat then you for sure might have a blown HG. Very well known issue with non OEM t-stats with subarus. Only use the thermostat you get from the parts dept at the dealer. Same goes for the cap if you replace that
 

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Yes only use a stock Subaru thermostat the cheap junk you buy at the local parts store will cause your subaru to over heat then you for sure might have a blown HG. Very well known issue with non OEM t-stats with subarus. Only use the thermostat you get from the parts dept at the dealer. Same goes for the cap if you replace that
The thermostat is housed in that elbow between the radiator and the engine block on the underside of the car, correct? Is there anything more to replacing the thermostat than pulling that hose (using a catch pan for the radiator fluid that will dump out once I've pulled the hose) to access the thermostat, removing it and replacing it, then putting the whole ensemble back together and re-filling the radiator?
 
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