H6 overheats at idle wtf...

Looking for a lil help,pretty stumped.The car is a 05 outback 3.0 with 190k. What happens is when driving the temp stays perfect without issues, a/c works,heat works. When it gets stuck in traffic or any type of idle the temp rises and overheats eventually,when I check the overflow tank,coolant has usually risen to the very top after this happens and doesn't always get pulled back in. I've replaced the coolant -oem and burped,I've replaced the the thermostat-oem,fans are running and kick on high speed when the issue occurs,radiator is roughly 6 months old but is from rock auto-denso version. Head gaskets have not been done to my knowledge. No oil mixing,no lose of coolant,no visible leaks.Any help would be allot

 

I ran into that with the rsvx. I had two issues going on. Someone also had the fan wired backwards so it was pulling hot engine air through instead of from the outside.

Then I found pure coolant wasn’t cooling enough so I added water to it and I’ve seemed to stabilize. I would add some water then watch it and test it before winter so you don’t freeze. I didn’t have to add too much but still something to watch.

 

Sounds like an airflow issue.

First off is to see if the fans run in that situation.

If they are working, I'd pull the radiator out, and wash it. The radiator fins are tighter than the condenser, so it's not uncommon to have debris pass through one, and clog up the radiator.

 

^ ...and burp it again, you may still have air in a bad place.

 

Hell yea advice/guidance! Fan is pulling air in correctly, I have burped the system twice. Radiator is less than 6 months old.

I think im going to wash the radiator out while its in the car thw best I can, pull out 1/2 gallon of the 50/50 mix and replace it with water. Ill report back, thanks again

 

Jacking the front end up, burping hoses running it with a funnel and a puddle inside funnel, running up to temp and revving around 2-3k when at temp. Air bubble was my first suspect.

 

I do not recommend changing your coolant mix, that's opening a can of worms (lower boiling point, less corrosion resistance, not to mention freezing point) for a band-aid at best (if it fixes your symptom, you still have a problem). 50/50 is perfect.

So you have to add coolant (or transfer it back to the radiator) after this happens? Coolant expansion is normal/expected (that's why the tank is there), but if it's not pulling it back into the system, then you have a different problem.

I still wouldn't do anything else until I could pull the radiator, and rinse it out (against the airflow), and rinse the condenser as well. If it's a fairly new radiator it shouldn't be clogged, but maybe the condenser is.

If you haven't replaced the rad cap, it might be a good idea to test that.


Might not be a bad idea to to a hydrocarbon test, but HG failure on these usually causes overheating under load (on the highway) more than at idle, so I'm not sold on that.

 

So today I pulled the grill and thoroughly cleaned the condenser even though it looked spotless. Also did what I could to clean the radiator but like I said relatively new. Drove the car around for about an hour without issue,let it run in the driveway for about an hour without any issue.... Kinda sat and shook my head for a bit, restarted and ran for abour 5 mins this time without a/c not sure how that would make it harder on the car, and it climbs to just under the whitw hash mark on the H side, so maybe 3/4. Im going to see if my 07 legacy s rad cap will fit on here, seems like it only overheats when the fan motors ramp up.

I never add any coolant I just transfer it back over

 

I should say that I added water to my pure coolant not 50/50.

Also I’m pretty sure any Subaru dealer can pressure test the radiator caps. I had Bloomington Subaru test one for me. Doesn’t hurt to fall and ask.

 

Threw a new OEM rad cap in there yesterday,same issue, no change

 

Temp sender?

As far as coolant not being pulled back into the radiator, I'd replace the hose from the radiator neck to the coolant bottle. If there is a crack in the hose it can pull air from the outside rather than pull coolant up from the expansion tank as the engine/radiator cool.

 

This is a big clue. If the cap isn't suspect, and the hose between the rad and overflow isn't clogged or damaged, you definitely need to test for hydrocarbons (Head Gasket).

That's not a Subaru-specific tool. One (or many) of the mechanics likely personally own them. Most auto parts stores can rent them for free (we certainly did when I worked at AutoZone).

 

Hydrocarbons test next I guess. Yay

 

Ok so last week,I gave it a block test came out blue out of overflow and a blue green from the rad,looked over the small hose looked good,completely burped system for about 45mins taking all proper steps, issue went away until yesterday when it started to rise slowly again. Noticed overflow full again block tested while its on the verge of overheating have the same greenish color, filled radiator swapped the hose, had the wife rev the motor and definitely could see smaller bubbles after burping it completely. Also larger bubbles immediately after shutting the car off.... Early internal head gasket failure??? Any other ideas???
Thanks for the help, much appreciated in these dismal times

 

Yuck...sounds like head gasket seep, indeed.

Labor for head gasket replacement on a 6-cyl usually costs more than a good used (or jdm) engine. With that in mind, I'd be very inclined to try some mechanic-in-a-can, there is a chance for heater core/radiator clogging, but usually minimal if done correctly.

Subaru makes a coolant conditioner, but I've heard good things about that. It's like only a few dollars (since it's actually a recall part number for the older 4-cylinders) at the dealer and is pretty easy to do, just make sure to keep the engine hot for sometime (15 minutes or so, IIRC) when you put it in, I guess when they first started doing this, some guys would just dump it in the radiator, and drive the car outside and park it, and it would set up too quickly and clog things.

Otherwise, I've heard very good things about the Blue Devil head gasket sealant. It's more like $60, and a pretty in-depth process....

 

I thought that was used mainly for external leaks? That's going to be the shot in the dark regardless for me,thanks for all the help! I'll post back with how it works out

 

I believe the Subaru conditioner is geared more for external leaks, but I've heard good things about mild internal leaks, as well. Worth a try...

 

Threw the conditioner in, overheated about a week later. I'm just going to have to play the transfer dance for a while.