I would pressure test the new radiator cap. If the radiator cap is venting at 1.3 bars (18.9 PSI), the fluid temperature is ~270f and you have a blockage somewhere.

 

How would I go about that? The cap is brand new from Subaru

Reply

 

Test for hydrocarbons from a head gasket leak. If no hydrocarbons, suspect a blockage in the heater core or radiator. Went thru this on my 05 OB. Ended up replacing the heater core, a PITA.

 

Did you do this work yourself?

How did you go about ensuring the cooling system was properly burped of trapped air?

Chris

 

Yes I did it myself, I used a no spill funnel

 

Which engine? I'm assuming you made sure to get the thermostat to open and checked for heat from the HVAC? I did the coolant change on my 3.6 last spring and it was definitely reluctant to burp, even with the front end on ramps and a burp funnel. I tried to follow the FSM procedure to the best of my ability and it ultimately worked out fine but, after reading of several struggles posted around here, I kept a close eye on it for a couple days using a wireless OBD scanner and Torque Pro. I don't like waiting for the idiot lights to warn me of anything.

 

It’s the 2.5, I let it run for roughly an hour, then drove around for 2 or 3 hours. I’d imagine the thermostat had to have opened in the time but I can’t say for certain

 

Well, if that's all you did, then I wouldn't be surprised if there's still a good amount of air in the system. For one, if you didn't turn on the heat, then I think the heater core will likely have a lot of air in it.

 

Yes I turned on the heat. Drove it for roughly 3 hours with the heat on

 

What led to replacing the thermostat in the first place?

Are the radiator fans coming on? Both of them? Does the AC work? Are you getting strong heat from the heater all the time, even when it's running hot?

Somewhere on this forum someone reported getting a radiator cap from Subaru and it was bad. It happens. If the cap isn't venting properly, the higher pressure increases the coolant temperature. It would also create what you describe where the light comes on, then goes out coupled with the "boiling" in the reservoir. It's a possibility. Not saying that's the problem.

Hydrocarbon test on these engines does not work. You have to monitor a funnel for bubbling, or watch data in conjunction. I gave up on hydrocarbon reating a boxer years ago since it can show passing and a HG breach is there.

 

I changed changed the thermostat because I was replacing the coolant. I replace coolant because I was experiencing “high temperature” warning but no visible overheating and spillage from the overflow reservoir. Someone here said there’s likely air in the system and low coolant due to heat fluctuations in the cabin.

Sometimes info feel high heat from the vents even with the heat off.

last night I parked the car and for the first time since I’ve owned it. The radiator sucked up coolant from the overflow but the coolant in the radiator filler neck was low

 

Thanks cardoc. I thought the purpose of increasing pressure inside the radiator was to raise the boiling point of the coolant. Hopefully I’m not confused. Here is credible description: Engine Cooling System 101: Keepin it Cool

 

Maybe I was misunderstood. The higher pressure does increase the boiling point. But, as soon as the liquid is no longer under pressure, hitting atmospheric pressure upon release, it's still at a really high temp so you'll see "boiling".

 

Just a note, OBW is Outback Wilderness, introduced in Gen 6. You don't have one from 2016. I doubt it matters for this issue but for some problems calling it an OBW may lead to incorrect responses as people might think Gen 6 and Wilderness trim (which does have a few mechanical differences from other Outbacks even of the same generation) when you apparently have a Gen 5. Unless you have the model year wrong.

Maybe yours wilderness green in color. It's a little unfortunate that Subaru reused a color name for a trim level.

Anyway, good luck with your radiator issue. Sorry I don't have any tips for you.

 

Just a note, OBW is Outback Wilderness, introduced in Gen 6...

I believe if you go a ways back, to the early days of this forum, you'll see that OBW had a different meaning, but one which is no longer valid. It was used to differentiate between the sedan and wagon version of the Outback. OBW = Outback Wagon.