2000 subaru overheating

my friends mechanic is telling him his 2000 outback (2.5 4 cyl) has a blown head gasket. there is NO water leaking/seeping out from anywhere outside the motor AND there is NO water in the crankcase motor oil. the thermostat has been replaced. the cooling fans work. I’m inclined to say it’s a plugged radiator. he is considering replacing the head gasket (to the tune of $1500+) on advice of his mechanic. is it possible to have a blown head gasket and not be leaking coolant?

...is it possible to have a blown head gasket and not be leaking coolant?

Yes, very common. Exhaust leaks into the cooling system.

First off, head gasket problems on Subarus are not an uncommon thing discussed here. And this vehicle is 15 years old. The problem seems to be more common on certain models than others, and certain years. You might use the search feature at the upper right to see if there’s other posts on this topic for this particular car.

There are 5 common ways coolant can exit the cooling system: (1) leaking onto the ground, (2) escaping into the air as steam or water vapor, (3) leaking into the crankcase oil, (4) leaking into the engine cylinders and out the tailpipe, (5) leaking into the automatic transmission fluid.

There’s various tests that can detect which paths are involved. A cooling system pressure test for example. Suggest to not put the cart before the horse. Overheating doesn’t necessarily imply a head gasket problem or even that any coolant is being lost. So the first question is: Is there any evidence of coolant being lost? For example does the friend need to top off the coolant occasionally to keep the cooling system full? If so, how often and how much coolant do they need to add? Is there any white smoke coming out the tailpipe after the engine warms up?

It’s also very common to have a headgasket breech without contaminating the oil.

Engines’ headgaskets contain combustion pressure and gasses and seal the channels through which oil and coolant pass between the block and the head(s). They often even seal the top of the water jacket.

A breech could occur between a combustion chamber and the cooling (water) jacket (the most common kind) and result in overheating and loss of coolant WITHOUT leakage to the outside world. With a breech of this kind, the piston will draw coolant through the breech on the intake stroke and into the combustion chamber where it gets burned (turned to steam). It will also allow hot combustion gasses to be blown into the cooling system, heating the coolant faster than the engine’s cooling system can dissipate it and badly contaminating the coolant with combustion gasses. And as the coolant gets lost, the problem gets worse.

A breech could also be between the combustion chamber and an oil passage, contaminating and heating the oil and allowing the oil to be drawn into the combustion chamber and burned. The contaminated oil can also allow the bearings to self-destruct. This is not the common type of breech.

A breech could also connect the water jacket and the oil passages with the combustion chamber, causing contamination of the fluids, overheating, destruction of the bearings, corrosive damage to the combustion chamber parts, and all sorts of bad stuff.

I’m not of the school that thinks most overheating issues are caused by failed head gaskets.
The only way head gaskets should cause overheating is if the gasket is leaking coolant and the engine coolant level drops low enough to cause an engine to run hot OR there is a breech between a coolant passage and a cylinder.

What is not known is what diagnostic procedures were used to determine if a failed head gasket actually exists. There are several procedures which will verify a HG problem beyond all doubt.

Since the oil is not contaminated with coolant, there are no external leaks, and if there is no white smoke being belched out of the tailpipe then I would look for another cause of the overheating rather than the head gaskets.

ok4450, normally I would agree with you, but considering Subaru’s history with head gaskets, in this case it is a real possibility.

However, even with a Subaru, it should be tested and confirmed before jumping into that kind of repair.

THAT…is how the DREADED Subaru Head gasket failure presents itself. Subaru release updated Head Gaskets to remedy.

Yes it can have other causes…but ive followed this road so many times that suspecting the Rad and the T stat and all other suspects first is what we all do… But if you hear the name Subaru stated prior to hearing these symptoms… You skip right to the culprit…the head gaskets.



I’m fully aware of the Subaru head gasket issues but I’m just not eager to jump in and blame the head gaskets at this point UNLESS some proper diagnostics have verified there is a head gasket problem.

It’s going to be disheartening to spend 1500 on head gaskets, crank it up, and then watch it overheat a short time later.

OF COURSE… I agree with you brother OK44. Which is why to this day…despite knowing or leaning heavily toward the head gaskets. I STILL go through all the smaller things it could be…but on Subaru of that year… It inevitably ends at the head gaskets. Trust me Im not happy about it either.

But of course…do your normal checks… T stat…Rad…etc… Eventually you will cry in your soup when you realize the heads are coming off.

Has anyone reported the reason this was happening so much on these engines? It wasnt the case prior…or Since…but if you have the known years of Subie that were affected…and this is one of them… Those damn gaskets failed like Repeat Robbie who is still in High School at age 21 which is to say…over and over again.

Subaru released new updated gaskets…but what was the root cause I wonder… Damnit now I have to look it up…


Helps to have an infra red thermometer to check on Rad operation. You “shoot” all the little columns within the rad…the ones holding fluid… look for temp discrepancies… Then of course the T stat. These two things are cheap, easy and helpful.

But if you have ANY overflow or high pressure rad hose symptoms etc…you know where you are headed.

If Im not mistaken…these Subaru’s were able to fool me into thinking that it WAS NOT the head gaskets… I forget their precise failure modes…but they seem ok…and the overheating was presenting in a confusing manner. And if it fooled me…its gonna mess Big Time with non mechanics. I DO remember that about these failures…they almost seem ok…and just pick their own time to overheat.

Which is why I want to know now…what the final decision was on this Subject.

But yes…always…I do the pre checks before ripping two cylinder heads off any engine. But with that name thrown in (Subaru) …expect to be closer to Head Gaskets than further away. Sad but true.


A good source of information below… Just upon a quick search… The article mentions Subarus as well and their problems. The article is broader than that however and good info for those with inquiring minds. A LOT of good info here… If youre like me…when you read this type of thing you start wondering how any of this stuff even works at all let alone lasts as long as it does… But that is what Math is for…figuring this stuff out. LOL