Subaru Outback overheated. Mechanics say head gasket. Other reasons?

Asked by Guru3TZZC Jul 01, 2020 at 07:30 PM about the 2004 Subaru Outback 2.5i

Question type: Maintenance & Repair

I think there is something not quite right with Convenience Auto Subaru
Specialists who have worked on my car for 6 years.
Just put $3k into my 2004 Outback which is in pristine condition, low miles,
and after paying them, 10 days later my car overheats for the first time.
Now they say the car needs a new head gasket and that this new
issue is due to what was "a nearly undetectable oil leak in the gasket."
They said there was "no way we could have detected it" before I sunk 3k into
the car for brakes and general maintenance to keep the car running for another
2 years.
The head gaskets were replaced by Dunning Subaru in 2017 and I have driven
the car 12k miles in 3 years. Very little wear.

What is the issue? I took the car back to the mechanics 10 days after they
performed maintenance,  after the temperature
gauge was abnormally high. It was  into the red zone and has never
overheated in the past. I was driving doing errands, it was 85F out and nothing
unusual. I have done a couple short 5 mile trips since and no overheating just
to see if this is a fluke. There is no white smoke or exhaust, it is driving fine, no
sounds or knocking. I am not sinking another 3k into it to fix the head gasket.
And I'm not convinced this is a head gasket issue.

What other issue could be causing the overheating and how can I get this
properly diagnosed before selling it "as is" or spending more money?
Help! CH

4 Answers

65,400

You never mentioned that the thermostat was replaced if it was replaced already bleed air from system like this. Remove cap from overflow tank fill with antifreeze to full mark leave cap off and start vehicle and let idle as engine warms up antifreeze level in overflow tank will rise this is normal once vehicle reaches normal operating temp thermostat will start to open and level in tank will drop add more antifreeze to full mark then put cap back on. That should clear all air from system.

The head gaskets should not have failed after 12k miles but after 3 years there is probably nothing you can do about it. You should consider scrapping the car.

48,660

There are small probabilities that the original head(s) have cracks, weren't sent to a machinist to assure condition and flatness, were shaved too thin, or the head bolts weren't replaced or properly torqued. But since it ran ok for 3 years after the work it's hard to be sure. Before you continue at great expense, check the simple stuff. First note that the Subaru OE t-stats are EXTREMELY reliable and durable, and never fail. If a Subie dealer did the prior HG job they probably tested or replaced the t-stat with an OE one, of course, but it doesn't hurt to pop it out and assure that it's the proper wide-bore OE type. Next, remove and blow out the rear heater hoses, as a blocked one will starve the. cooling system of proper flow as their in-line and not in parallel. There's a chance the radiator is clogged from past use of sealer(s), as well. If it's a copper one then perhaps it's simply not sinking enough heat. Likewise if a cooling fan isn't switching on (check their switches and harness too). Finally, to purge the coolant of air it's best to lift the front of the car upward (or park on an uphill), put a funnel on the radiator hole, and keep adding coolant to it until all air bubbles disappear. If they NEVER fully disappear you may have internal "percolation" from a head gasket internal breach. This catastrophic high-pressure failure occurs less often in the 2000-2009 SOHC 2.5i than the very common HG atmospheric leak (loss of coolant on the left head and/or oil seepage to the outside world from the right head), but it IS possible. You are correct that there's no way I would countenance replacing HGs for $1.6k in a 16 year old Subie. But chase the cheap stuff first. Maybe you'll dodge a bullet. Good luck. Ern

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