I have used the search function and while there are tons of material on the DOHC and SOHC 4 bangers, there isn't a lot on the H6 engine. Now for my problem. I drove my 2002 H6 two hours at 60mph+ the other weekend, without stopping. When I arrived at my destination, I smelled coolant very faintly. Popped the hood and had a small bit of seepage from the top of the overflow tank, and the overflow was very full. It never overheated and never gave any sign other than the small amount of seepage. Drove back home later that day and parked it, (I have another car for work). Today I cranked it up and let it run and warm up to see what would happen. While the coolant level had dropped a little , it was still way above the full mark on the overflow. I also noticed an occasional bubble coming from the overflow hose. ( I made sure it was the overflow hose.) I know this usually means a blown (not leaking) head gasket. I also know this is mega uncommon on the h6 and is there anything I can do other than a hg job that might be the problem. I do all my own mechanic work, since that's what I do for a living so money is not an issue. Other than the money for a HG job, which is what I am trying to avoid. If anyone has any ideas, let me know.

 

 

Also, as a side note. Does the Subaru coolant additive work for blown as well as leaking head gaskets? It seems like it wouldn't. Just wondering. Also, what kind of coolant would be best. I'm not looking to get out cheap so if I have to buy Subaru brand coolant I will. I'm really not wanting to do the head gaskets on this car as I just bought it a month ago( wasn't doing this at the time) and would prefer not to spend $3000 more dollars. The car has 97,000 original miles.

No amount of coolant additive will fix an already bad head gasket.

 

This is not as uncommon as you might think. We've seen several threads here recently concerning bad HGs on the H6 engines. SubaruOutback.org has more.

They tend to make it into the 200k range before having problems, but over 200k miles You should expect ANY engine to have possible head gasket issues.

I wasn't saying that an additive would fix it. Also my car only has 97,000 miles. I was asking about things that I could do to maybe fix the problem in case it wasn't a head gasket issue.

Replace the radiator cap first, make sure its from Subaru too. This fixed a weird overflow/bubbling issue I had with our h6 vdc outback.

Install a Subaru radiator cap.

 

I would bet a lot of money this issue is why it was traded in/sold and it had the issue when you bought it, it just didn't exhibit symptoms when you bought it.

 

It sounds like a headgasket. I've seen them do exactly what you're describing.  The H6's can get worse veeeerrrrrrryyy slowly.  I've seen them run two years like this before they start overheating due to worsening conditions. I've seen them only overheat for two summers with the A/C on while idling.  It seems they start as as very small leaks and progressively get worse.

 

Your suspicion is correct, conditioner/additives won't work when they do this - it's blowing exhaust gases into the coolant.

I am going to drain the coolant, replace the thermostat (with an OEM subaru thermo) and replace the cap with a OEM subaru cap, then refill with Subaru coolant and see if I continue to have the problem. If I do, I guess I will have to bite the bullet and get the headgaskets done. *Sigh* and the reason I bought the H6 was to avoid this issue!

Update on this issue.  The H6 is loaded up and headed to the repair shop to be fixed after all this time. All OEM parts ordered. Updates will continue.