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I have a 2001 H6 that probably has a blown headgasket, and so it's curtains for the engine (and maybe the car). However, before I start searching around for a JDM or used engine, I want to make sure my heater core isn't also a source of the overheating problem. The A/C still works fine (unless the engine gets too hot), but the heater doesn't blow out hot air and help the engine stay cooler. Could this be a blocked heater core? No wet discharge from under the dash, which I understand is sometimes a symptom.

If it is a blocked heater core, are they easy to flush or unblock, or is it time to replace the whole car? I understand replacing the heater core involves taking off the dash for about $1200 labor, and if I'm replacing the engine as well, the car's not worth it.
 

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Could be a blocked heater core. Could be an air pocket due to low coolant. Could be a air pocket due to blown head gaskets.

Do you have any of the typical head gasket symptoms? Bubbles in your overflow for instance? I assume the engine is running hot since you're trying to cool it off with the heater.

You'll need to purge the cooling system of air somehow. Lots of people use spill free funnels and putting the front of the car on jackstands. Once you've got the air out of the system, then you can start diagnosing proper.
 

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I have a 2001 H6 that probably has a blown headgasket, and so it's curtains for the engine (and maybe the car). However, before I start searching around for a JDM or used engine, I want to make sure my heater core isn't also a source of the overheating problem. The A/C still works fine (unless the engine gets too hot), but the heater doesn't blow out hot air and help the engine stay cooler. Could this be a blocked heater core? No wet discharge from under the dash, which I understand is sometimes a symptom.

If it is a blocked heater core, are they easy to flush or unblock, or is it time to replace the whole car? I understand replacing the heater core involves taking off the dash for about $1200 labor, and if I'm replacing the engine as well, the car's not worth it.
It's not the heater core, it's the headgaskets.

Refill coolant and burp all the air out of it.

Don't let it run hot/boil over. Then look for bubbles in the overflow tank. Keep track of coolant contumption every time before you drive it, top it off in the radiator (not hte overflow). You want it to stay topped off and avoid boiling/blowing coolant out the overflow.

With the coolant FULL and NO AIR in it, start the car with the heater on high. You'll get heat (suggesting the heater core is fine) until enough exhaust gases bubble into the coolant to disrupt proper coolant flow.

There's the distinct possibility that if this headgasket has been left too long (like you just bought it like this so it's been failed for a while or it's been nursed along/ignored) - then the bubbles may build up fast enough to disrupt heat flow too quickly to do that simple test.

Subaru heater core failure is rare, not common. Every time I hear "heater core" - that means I have some diagnosis to do because that suggestion has been historically wrong 100% of the time for decades now. Even in the rare Subaru's that do have a failed heater core you get leaks or no (or reduced) heat in the cabin without overheating.

So let's assume this car is the outlier magical unicorn subaru heater core which failed just in the right way to miss all those normative failure modes.

Nope, not a chance. Or more accurately - yes, diagnosis it properly and find out what's wrong for sure - but let the data lead that direction rather than look for it. As CS Lewis said, "suspicion often finds what it suspects".
 

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Thank you for the suggestions. I've made good use of the spill-free funnel recently. I'll get the system pretty well purged of air - the bubbles will stop coming out - but if you wait long enough the level of coolant in the funnel will rise and some small bubbles will appear. They aren't huge, roiling bubbles and I don't hear any bubbling over into the overflow tank or anywhere, even if the car is hot.

I've replaced the thermostat and the radiator cap with Subaru OEMs twice each. For most of the summer, it drove well, with the temp gauge sitting just under half way up, as it normally does. But clearly there was some sort of leak in the HG allowing air in and pressure to build. My son was driving it on a hot day about three weeks ago, and he said the temp gauge rose steadily, to red by the time he got home. I looked at the engine and the previous owner had put a plastic flushing tee on one of the heater hoses, and the plastic cap had shattered. I replaced the hose with a new one, and didn't put in another tee.

Many purges later,the car would overheat pretty quickly, especially at higher speed or after going up a hill. So I'm pretty sure the HGs are done. Oddly enough, after posting this last night, I took the car out for a 5-mile round trip test run that involves a 55 mph road, and it overheated about halfway through. I pulled over for about 10 minutes to let it cool off, and then drove back home. I had the heater on the whole time and got no hot air out the vents. Then, just before I got back home the temp gauge moved to the red zone and the heater kicked on full blast, no problems. So I think you're correct that the heater core is fine.

Latest problem notwithstanding, it's overall been a good car, and perhaps more importantly I've learned a lot about Subaru maintenance. For those reasons, I'm inclined to have a used or JDM engine installed. To me, the JDM seems the way to go. Would you agree, or are there compatibility issues?
 

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First off, when you are burping the air out of the engine and cooling system, after it's run a bit, you have to rev the engine up to about 4k rpm once or twice to force coolant through the heater core and push out any air. In burping the car, if you don't have heat when the engine comes up to temp, you have air trapped in the heater core and coolant isn't flowing through it. When you have heat while burping, then you run it til the bubbles stop.
In your case, a rise in the funnel is an indication that the HG is compromised and combustion pressure is getting in the coolant. It only takes one time sometimes to blow the HG.

As for the JDM engine - You will have to use your AC compressor as the JDM compressor is different. You'll need a longer vacuum hose for the brake booster because the nipple for the booster is on the opposite side of the engine. You will NOT get it out without a lot of heat and force. Same with the plug that is on the bank 2 side. So just get a longer hose that won't kink between the brake booster and intake.

Change out the thermostat with your new one. Put in new spark plugs while the engine is out. Clean the throttle body and intake good (removing the torque converter bolts and installing the bolts is easier with the intake off the engine; you have a clean straight shot at the bolts). If there is any sign of valve cover gasket leaks, change those also, just don't use FelPro. They don't fit right. MAHLE. Also, get an oil cooler gasket from Subaru or the parts store and change that out while the engine is out.

Otherwise, it's all the same. You'll have an extra PS pump and Alternator. Maybe a belt if it's good. Clean all your engine ground straps while the engine is out and correct any issues with the battery cables. Good time to clean the engine bay if it's dirty.

You may also consider catching up other things that may be due like trans fluid and filter (under the front fender behind the fog light), along with front and rear differential oils.

If you have any issues, post up on this thread so we can follow it and assist.
 

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So I think you're correct that the heater core is fine.
Right - it's not the heater core. You're tracking.

For those reasons, I'm inclined to have a used or JDM engine installed. To me, the JDM seems the way to go. Would you agree, or are there compatibility issues?
I'd go with JDM but those older EZ's aren't as common now. Most of them are the newer ones for 2005+. But should be some floating around?

If you can find a local engine reasonably priced with some known history to it then maybe you have a good option available. That's just hard to do usually. Local ones usually have an unknown history - they come from auction/trade in with no background.

Are you close to the east coast? I have a 2003 Outback H6 I could probably sell the entire car for the price of an engine.
 

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You look for one with an aluminum intake. If it's the plastic intake, most likely its an AVLS engine which will not work with your ECM.
 

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Discussion Starter #8
Right - it's not the heater core. You're tracking.

I'd go with JDM but those older EZ's aren't as common now. Most of them are the newer ones for 2005+. But should be some floating around?

If you can find a local engine reasonably priced with some known history to it then maybe you have a good option available. That's just hard to do usually. Local ones usually have an unknown history - they come from auction/trade in with no background.

Are you close to the east coast? I have a 2003 Outback H6 I could probably sell the entire car for the price of an engine.
Thanks, gents. idosubaru, I'm in Virginia - where are you? Definitely interested in the 2003...
 
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