My Son has an 08 Subaru wagon with the 3.0. A few weeks ago it started running hot on a road trip. A shop in the area diagnosed it as leaking transmission cooler lines on the bottom of the radiatior, replaced the clamps, topped him up, told him to get them replaced whe he got home.
I figured with 176k miles, might as well replace all of the hoses, etc. Last week I did a new radiator, thermostat, and all hoses. I used factory Subaru hoses, and even bought Subaru hose clamps, it ran hot again this Sat. I just looked at it, coolant was down a little, I see no leaks, both fans work, etc. Is there anything on this motor I need to look at? Oil looks fine, I just ran it for an hour, no issues. I hate intermittent issues....
11GTCS
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9/13/20 8:59 p.m.
1988RedT2 said:
Um. Head gasket?
Quoted for truth. Sorry man.
That's what I'm afraid of but with nothing from the tailpipe, and nothing in the oil, im confused. Wouldn't there be something?
You said you used Subaru hoses, did you use a Subaru thermostat or aftermarket?
Im not sure is the 3.0 is the same way, but the 2.5 we had in our forester would run hot on the highway with an aftermarket thermostat, but was fine with a Subaru thermostat.
I don't have any firsthand experience with the H6 engines, but the word on the street is that 3.0 H6 isn't as bad for head gasket issues as the 4 cyl Subarus, but it does happen sometimes. I would make absolutely sure that there aren't air pockets in the cooling system before condemning them though, Subies need a lot of "burping" to get the air out. The failure mode on the old phase 1 EJ25 4 cyl engines was exactly this- combustion gasses getting in to the cooling system, usually at first only under high load use. Since the pressure in the cylinder is so much higher than the pressure in the cooling system when the head gaskets get weak the flow is combustion chamber gasses >cooling system rather than the other way around, so you're not going to see white smoke out the tailpipe or a milkshake in the oil.
And +1 on the OEM thermostat as No Time mentioned.
Get one of these and stick it in the radiator/exhaust. I rented one from Autozone.
Thermostat came from the Subaru dealer, I like to use oem ones when I can. I'll try burping the system more if possible. From what I saw the 3.0 didn't (usually) have head gasket issues, and I'm really hoping it's not one....
I'll grab a leak detector kit anyway, wouldn't hurt. I appreciate the suggestions.
Subaru H6 had less of an issue with head gaskets but it still occurred. I replaced them on my SVX at 147k as it overheated.
Headgasket or system need burped.
Please follow up with us when you get a diagnosis. I hope it's not the HG. Good luck.
wawazat said:
Subaru H6 had less of an issue with head gaskets but it still occurred. I replaced them on my SVX at 147k as it overheated.
Different species, though. Your SVX had a biggiesized 2.2. The 3.0 is completely unrelated to the EJ family.
How hot is running hot?
Pete. (l33t FS) said:
wawazat said:
Subaru H6 had less of an issue with head gaskets but it still occurred. I replaced them on my SVX at 147k as it overheated.
Different species, though. Your SVX had a biggiesized 2.2. The 3.0 is completely unrelated to the EJ family.
How hot is running hot?
Enough to set off the warning light, as in overheating. I have a new cap and non spill funnel coming Tomorrow, I'll use that to get all of the air out, and see what happens.
Has anyone used the Harbor Freight detector? Any good?
What do the transmission lines have to do with running hot?
In reply to wvumtnbkr :
Transmission cooler lines, leaking at the bottom of the radiator, so it was losing coolant.
Just a shot in the dark here as all of my Subaru's have been sticks but my sister had a late 90's Outback and it had a warning light for the transmission temp, are you sure the light you are getting is for the engine and not that? I haven't noticed anything other than the temp gauge on mine.
Just dug up the owner's manual online and that light is AT OIL TEMP so I doubt that is the issue.
adam525i (Forum Supporter) said:
Just a shot in the dark here as all of my Subaru's have been sticks but my sister had a late 90's Outback and it had a warning light for the transmission temp, are you sure the light you are getting is for the engine and not that? I haven't noticed anything other than the temp gauge on mine.
That's the photo he sent me, I have no idea what light he meant as I've never driven the car until after I replaced the radiator
Correct me if I am wrong. But I always thought the cooling lines going from the transmission to the lower part of a radiator on automatic cars carried ATF and not coolant.
If I am correct above and they were leaking, that has nothing to do with your issue.
On the HF leak detector. I am sure its fine, its just a liquid that changes colors when in contact with combustion gases. Now, if your headgasket is leaking out and not coming in contact with the combustion chamber, it might show negative while still having a problem.
In reply to Slippery (Forum Supporter) :
I have seen radiators leak coolant at the trans cooler passthroughs. This is a bad radiator, not trans lines.
Slippery (Forum Supporter) said:
Correct me if I am wrong. But I always thought the cooling lines going from the transmission to the lower part of a radiator on automatic cars carried ATF and not coolant.
If I am correct above and they were leaking, that has nothing to do with your issue.
On the HF leak detector. I am sure its fine, its just a liquid that changes colors when in contact with combustion gases. Now, if your headgasket is leaking out and not coming in contact with the combustion chamber, it might show negative while still having a problem.
Now that I think about it, they did. I was just going off what he told me and the report the other guy wrote up. It recommended replacement of "2 transfer coolant lines, trans coolant hoses, radiator, and thermostat" due to leaks and overheating. I figured with the miles it wouldn't hurt to just do it all anyway since I was there. Now that I've had time to think about it logically, those lines have 0 to do with the overheating issue, must have just been on the "while you're there" list, like a water pump when you're doing the timing belt.
I did a quick "swap parts" job then went out of town for a week, now that I'm back and can dig into it more without being rushed, I'm sure I can figure it out, I'm just paranoid it's the head gasket.
Steve_Jones said:
In reply to wvumtnbkr :
Transmission cooler lines, leaking at the bottom of the radiator, so it was losing coolant.
Wouldn't transmission cooler lines leak transmission fluid? That part of the radiator has trans fluid in it sealed off from the water side.
Edit: Posted before reading to the end...
Floating Doc (Forum Supporter) said:
Please follow up with us when you get a diagnosis. I hope it's not the HG. Good luck.
I used a spill free funnel to bleed the system Yesterday, it seemed to have a good amount of air, so hopefully that was it. They drove it Yesterday and Today, no issues. The block test kit was delivered Today, so I just ran a few tests, and it shows all good. I'm hoping that it's fixed, and got to play with a few things I've never done before, so I'll take it. If it overheats again, it's pretty much down to the water pump, which I can replace if needed.
My main worry was the head gasket, and it looks like we are good there. I appreciate the suggestions.
Good news, man. Hope it stays that way.
