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Discussion Starter #1 (Edited)
Well it looks like I have a more pressing issue than my liftgate and hazard light deal.

I've been having some overheating issues that are intermittent. I've taken a variety of trips (in terms of duration, mileage, and ambient temp) and no specific case causes the overheating to happen. When overheating, an OBDII reader reads values past 230F, even concerningly reaching 240F a couple times.

I checked my coolant reservoir and noticed it was waaay below the empty line, so I filled it up. I then drove the car for a day and thought the overheating fix was as simple as that. Then I noticed it started overheating again the next day. When I stopped the car, I saw a small amount of leaking coolant, and it was a little milky. I let the car cool down and popped the radiator cap off, and sure enough, that coolant was a little milky too.

Fearing the worst, I set up an appointment next Tuesday to get the car evaluated for a possible HG failure. But after some more searching, there are other things that point me towards an oil cooler problem, or at least away from a headgasket problem.

  1. There's been a small leak by the oil filter since I've owned the car (1 month). I thought this was the passenger valve cover gasket leaking down (since it IS leaking), but I think now that it might be the oil cooler gasket.
  2. There seems to be no coolant in the oil. If I check the oil dipstick, it comes up clean. The oil cap is clean too.
  3. The radiator and hoses look ugly. There seems to be a small coolant leak (I can't pinpoint it yet) from the radiator itself, the hose clamps are rusty, and the coolant just looks gross in general. I'm thinking of doing a full coolant flush with Subaru coolant conditioner, replacing all hoses and clamps, and evaluating if the radiator needs to be replaced from there (if I'm still getting leaking).
The main thing I'm wondering now is if an oil coolant gasket failure, or failure of the entire unit can cause oil to mix with coolant, but not vice versa. Then I'd hopefully have a non-headgasket issue on my hands.

(Sorry for the wall of text.)
 

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until this is resolved, always confirm coolant level in the radiator.

details on car?

I have read MANY posts about HG internal failure but, it's usually combustion gasses. That said, I have NEVER read of the oil cooler allowing oil into the coolant.

it may be 'fiddly', but I think the oil cooler can be bypassed for testing purposes. Loop the coolant back with a coupla small tubes and small length of hose? Probably need some kinda ThoroFlush or similar before refilling the cooling system for testing.
 

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Discussion Starter #3
until this is resolved, always confirm coolant level in the radiator.

details on car?

I have read MANY posts about HG internal failure but, it's usually combustion gasses. That said, I have NEVER read of the oil cooler allowing oil into the coolant.

it may be 'fiddly', but I think the oil cooler can be bypassed for testing purposes. Loop the coolant back with a coupla small tubes and small length of hose? Probably need some kinda ThoroFlush or similar before refilling the cooling system for testing.
So just rig up some hoses so that the oil cooler is skipped, and the coolant to the oil cooler hose instead routes right back into the cooling system, right?

Would something like this be useful? https://www.amazon.com/Block-Tester-BT-500-Combustion-Leak/dp/B06VVBSFTF I'm thinking that checking for exhaust gases in the coolant would tell me for sure if it's a head gasket failure or not.
 

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yeah, just a bypass - I suppose you could also monitor for oil coming out of the cooler 'pancake', if you don't see anything, tape or plug the opening so road dust/dirt doesn't get in there.

the block tests have been very disappointingly inconclusive. And, most cars with typical HG failure have coolant blown into/out of the overflow and frequently have streams of bubbles coming out of the coolant too.

I have been known to suggest sending a coolant sample to Blackstone or maybe Polaris labs - they can probably confirm combustion products in a sample.

It's worth noting the H6 has an interesting situation with its waterpump's design and 'maybe' there's a way a seal or 2 could fail allowing mixing of oil/coolant at that location. Do you have any spots dripping from a weep hole near the thermostat area under the front of the engine?
 

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Discussion Starter #5
Do you have any spots dripping from a weep hole near the thermostat area under the front of the engine?
I think so? I thought the leak I spotted came from the radiator itself, but there is dripping in that region. You mean the lower radiator hose that connects to the block, right?

I did a lot of research today and I might have scared myself more than I should, originally. I know for a fact that my coolant is filthy and the hoses/clamps should be replaced, so I'm going to do several coolant flushes and replace hoses and clamps today. And I'll also replace the oil cooler gasket, oil, and oil filter while I'm at it. Then I'm going to see if there's still a leak and/or overheating after that.

Does that sound like a solid plan?
 

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I think so? I thought the leak I spotted came from the radiator itself, but there is dripping in that region. You mean the lower radiator hose that connects to the block, right?

I did a lot of research today and I might have scared myself more than I should, originally. I know for a fact that my coolant is filthy and the hoses/clamps should be replaced, so I'm going to do several coolant flushes and replace hoses and clamps today. And I'll also replace the oil cooler gasket, oil, and oil filter while I'm at it. Then I'm going to see if there's still a leak and/or overheating after that.

Does that sound like a solid plan?

Sustained high temps probably aren't being caused by your leaks. I think the leaks are a correlation, not causation. It's good to patch those leaks up obviously, but, as far as overheating, I think even once the leaks are fixed you'll still find yourself running hot.

If it's running hot, no matter the ambient temp or no matter the condition--city driving, freeway, at a stop light, really it all sort of points to the radiator. These cars are getting up there in age and there's been lots of people with similar issues that are finding their radiators externally clogged between the radiator and the AC condenser.

While you've got the hoses off the top, pull the two 10mm bolts holding the radiator brackets to the upper radiator support. Push the radiator forward and have a look down in there.

I put a light behind this radiator for all to see just how clogged they get--
469924
469925
469926


That radiator was out of a 2011 w/ 140k miles. The car blew headgaskets 3 times before I got my hands on it.
 

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Discussion Starter #7
Okay, I was wrong. There isn't oil in the coolant, so that's a big phew. However, it is dirty as all ****. So I bought coolant flush and drained the coolant. Not even close to 7.6 quarts flowed out. It was more like 1.5 gallons, which I guess is expected since I wouldn't expect all the coolant to drain fully. I then dumped in the coolant flush, along with some new coolant. I started the car and blasted the heat, and what do you know...? No heat. None at all. Maybe the heater core is clogged?

Funnily enough, I ran across your thread @aesthetic.rake (https://www.subaruoutback.org/threads/the-case-of-the-overheating-h6.495737/) and those symptoms are literally what I've experienced in the past. And my car is at 208k miles. Spooky. Did that thread have a final outcome? I've started to dig into it a bit, but 31 pages is quite a lot.

The radiator is clean, by the way - externally at least. I'm sure the inside is pretty gunky.
 

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Okay, I was wrong. There isn't oil in the coolant, so that's a big phew. However, it is dirty as all ****. So I bought coolant flush and drained the coolant. Not even close to 7.6 quarts flowed out. It was more like 1.5 gallons, which I guess is expected since I wouldn't expect all the coolant to drain fully. I then dumped in the coolant flush, along with some new coolant. I started the car and blasted the heat, and what do you know...? No heat. None at all. Maybe the heater core is clogged?

Funnily enough, I ran across your thread @aesthetic.rake (https://www.subaruoutback.org/threads/the-case-of-the-overheating-h6.495737/) and those symptoms are literally what I've experienced in the past. And my car is at 208k miles. Spooky. Did that thread have a final outcome? I've started to dig into it a bit, but 31 pages is quite a lot.

The radiator is clean, by the way - externally at least. I'm sure the inside is pretty gunky.
We're still working on it but my window for diagnostics is closing pretty fast.

More than likely your heater core has air in it. These things can be a bitch to get all the air out of.
 

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Discussion Starter #9
We're still working on it but my window for diagnostics is closing pretty fast.

More than likely your heater core has air in it. These things can be a bitch to get all the air out of.
Flushing it by sticking a garden hose in the input, then flushing again by doing that in the output doesn't work?
 

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Flushing it by sticking a garden hose in the input, then flushing again by doing that in the output doesn't work?
Who said anything about that?

You opened the coolant system. With a Subaru engine, it can be tough to get all the air out. The heater core, unfortunately, resides at one of the highest areas the coolant has to get into and push the air out of. I'm saying if your heater core isn't working, because you opened the system, you've likely got air trapped in it the heater core, so, that's likely why you're not getting heat out of the heater.

The heater core being plugged and flushing it out is completely unrelated to what I was saying, but, I would say the hose trick you mentioned, should do the job.
 

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What year and engine are we talking about?

I didn't read it all - that's a lot of words for something as basic as overheating.

1. check for leaks
2. burp cooling system
3. keep radiator full - after every drive top it off
4. is it still overheating even when the radiator is full?
5. is it only overheating during high loads - up hills, high daytime temps, etc?

H6's commonly leak oil at valve covers and oil cooler gasket. Replace them. If you're replacing valve cover gaskets, do the spark plugs at the same time as they're really easy with the covers off. Replace the coolant hose with the oil cooler gasket.

The crossover metal pipes frequently rust in rust prone areas and leak throuugh the scaley rust.
 

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Discussion Starter #12
Before I lead us down a rabbit hole, I pulled the thermostat last night and noted that it didn't open with boiling water. So I'm picking up an OEM thermostat, t-stat gasket, and oil cooler gasket today. I'll install all that this afternoon, fill her up with fresh coolant, and see how she does after that. If it really ends up being something that simple...doh.
 

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Discussion Starter #13
After a setback (the replacement OEM t-stat was also bad), I got my hands on yet another OEM t-stat. I installed it last night, got some fresh coolant in there and burped it as much as I could (no exhaust gas smell during burping). I also flushed the heater core both ways, it was a little dirty. I drove the car to work today and temps seem to be sitting smack dab in the middle of the gauge! If all is indeed well, I'm lucky it was something so simple. I really went overboard with thinking the worst.
 

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That's the second time this month, that I'm aware of, a thermostat has failed. Both times I incorrectly diagnosed it as a radiator before thinking of the thermostat. Thermostat failures seemed rare until lately. Weird.

Glad you got it figured out.
 

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Discussion Starter #15
No sweat at all. Any and all help is always appreciated. I learned a lot about the cooling system through this whole experience and I'm sure I'll use all the helpful comments some time down the road. I'll be replacing the oil cooler gasket with the next oil change, and will be moving on to the hazard lights now...

Thank you everyone!
 

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I recently bought a 3.0r outback, and while I'm pretty sure its a headgasket or worse maybe yall can enlighten me...

Ok so test drive went well and all seemed fine except for a little white gel around the radiator cap. I was leery but that wasn't gonna stop me from finally getting my unicorn after 10 years of pining and waiting for a decent specimen. On the ride home i stopped for gas after 2 hours on the freeway and temp shot up as soon as i stopped at the pump. Added the entire overflow reservoir and about 10oz of water back into the radiator before topping the reservoir off with fresh 50/50. 2 hours down the road later i had to slow to 30 for an exit ramp at the end of the ramp i noticed the temp starting to climb again, but it went right back after getting on it and holding 60. When i finally stopped same issue. So i get it home and i do mostly short trips, it doesn't overheat but i can top it off and it will be down a quart in two days. Its definitely leaving out the reservoir, but i can go days without adding anything and itll be just fine temp wise. Cold start cap off, radiator topped off, it will be flowing out of the radiator in 30 seconds from start. No coolant in the oil, and seemingly no oil in the coolant, but i believe im getting exhaust in the coolant. Headgasket? Cracked head? 215k...
 

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Update:
Soo it looks like I was bamboozled. I drove about an hour from home on Monday, once i arrived the temp started climbing a bit as expected. Only this time when i went to add coolant it poured straight out the bottom. Turns out my radiator had a bad seam on the bottom. Luckily was able to get one shipped same day to an advance auto, and i was able to avoid having it towed. Anyhow i was under the impression i had a new radiator. It was soo clean and shiny up top, but here's what i think really happened. I think the radiator was bad before i bought it, it looks like the dealer stuffed it with petroleum jelly or some kind of similar fix to stop the leak and get it off the lot. Shined up the top to make it look nice and i bought it. Anyhow, after my drive home all my fluids stayed right where I left them, i added about a pint to the radiator and reservoir this morning after 2 days of short trips to work and back, probably just residual air. I'll be sure in a week, but it seems like this was my problem all along, and not a headgasket. I'll be sure to flush the whole system once I'm sure theres no other issues. Im soo happy that i won't have to sink another 1000 into it.:p
 
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