overheating, possible HG

[mva5142]

I recently became the owner of a 98 legacy outback with 80,000 miles on her. It has the 2.5l dohc. It overheated and after searching through the posts on here I think it is the headgaskets. It overheated fast, cooled down to normal operating temp fast, and the lower radiator hose is much cooler than the upper. I have a couple questions so far.

 

1) why is there such a dramatic difference in the hose temperature?

 

2)There are no air bubbles or oil in the radiator or fill cap or water in the oil.

 

3)The car can idle all day and not overheat, why is this.

 

4)Can someone smarter than me explain why the headgasket leak causes these particular issues?

 

I have never worked on flat engine. I have done a couple head gasket jobs in the past on a rodeo and a mustang, is this engine especially complicated. Does the engine really have to get pulled to take the heads off?

 

Thanks all, looking forward to joining and participating in the community here.

 

Matt

[Gloyale]

Drastic difference in Hose temps are often a sign that there is a cheap thermostat in there. I'd start by replacing that with a Genuine Subaru one. There is a BIG difference in construction and operation.

 

Beyond that, it isn't absolutely nessecary to pull the engine, but it really helps. The DOHC heads are so big it's very hard to get them out. Plus the bolts hit the framerail when you try to slide them out, so you end up having to unbolt the motor mounts and lifting the engine a tad anyway.

 

For 2.2 I leave engine in car, for DOHC 2.5 I pull them.

[idosubaru]

not all makes, models, and engines behave the same when similar things fail. you're experiencing typical EJ25 head gasket failure symptoms. very common. of course you want to rule out other possibilities like a leak or bad t-stat like GLoyale said.

 

sounds like you may have unwillingly been sold one with a pre-existing problem. sorry to hear that if so.

[mva5142]

I would hope that the issue was unknown, but I will never really know.

 

I am going to change the t-stat, water pump and timing belt and see how it does.

 

Why is the overheating with a headgasket random? I would think that it would be pretty regular. I test drove it for 15 minutes or so, and then about 100 miles home before it overheated. What makes it so random?

 

Thanks for the guidance.

[idosubaru]

would you expect a bubble the size of a pin head in the coolant to cause overheating? no, of course not. how about 2 bubbles? 100? 10,000? well it depends where and how quickly they coagulate.

 

sounds like there's plenty of room to be random given different temps, RPM's, water pump hydraulic properties..etc. you can search for pumps and cavitation to understand more about fluid pumping properties.

 

if you just bought the car....there's a chance they tried to toy with it to sell as well. conditioners, remove the thermostat, there's a few ways to try and cover that up.

 

air in the system disrupts coolant flow significantly in these engines. it prevents overflow coolant from being sucked into the engine to replenished what's lost. once the coolant loss is enough and air bubbles have gotten trapped in the right places...overheating happens.

[Rooster2]

It is possible that it is a bad water pump, but I doubt it.

 

With the 2.5 phase 1 motor, which you have, the head gaskets go bad by allowing exhaust gas to enter the cooling system. It is not a problem with coolant getting into the oil. The exhaust gas can cause the car heater to work poorly because of poor coolant circulation, while the added exhaust heat causes the temperature guage to spike quickly to "hot." This also causes such poor coolant circulation (because the cooling system contains some gas, not liquid, that the top hose will be hot, while the bottom hose is just warm. Air "exhaust bubbles' are sometimes seen in the overflow tank that sits off to the side of the radiator.

 

It is common to have a bad head gasket, but it only presents itself when the engine is being driven. It will idle all day without over heating, but just drive it, and put a minor "load" on the motor, and it will over heat.

 

Hopefully, you have not driven the car long with the engine being over heated. If not, replacing the HG will solve your problem.

 

Also, it is not uncommon for the bad head gasket problem to cause such heat and pressure problems, that the radiator springs a leak.

 

Replacement head gaskets from Subaru have been improved. The revised design seems to permanently solve the problem.

 

Since you just bought this car, I suspect that the previous owner may have known about the HG problem. Perhaps that person will pay for some of the cost of a HG repair. Can't hurt to ask, or maybe return the car and get your money back.

Edited January 16, 2009 by Rooster2

[mva5142]

Thanks for the responses. After being able to toy around with it over the weekend, it appears it is a headgasket issue. I let it idle for 30-40 minutes a day and it is losing water after it cools down. Also, I drove it about 5 miles and it overheated as I was pulling back in the driveway. I let it cool down and turned it off and it never pulled any coolant in from the resevoir even though when I checked it the next day it was low. I don't have the time or experience to change them myslef, never pulled an engine, so it is going to the mechanic this afternoon and should be back thursday evening. Not a good way to start off ownership of a new used car, but looking forward to finally getting it back and putting it to the test for the rest of the michigan winter.

 

Thanks again.

 

Matt

[idosubaru]

sorry to hear that, but glad you're having it done.

 

i'd ask the mechanic to use new Subaru head gaskets. since this is a 100,000 miles interval timing belt now is a good time to get an entire timing belt kit. it's not a good idea to expect all of the pulleys and the tensioner to make another 10 years and 100,000 miles.

 

not only because of mileage but because the components are over 10 years old. i picked up EJ22 timing belt kits on ebay for $80, it's a steal. i'd look into EJ25 timing kits.

 

this is an interference engine, if the belt breaks or the pulleys seize you are likely to incur significant engine damage.

 

this is a testimony to why i caution against EJ25 purchasing. tread carefully, it is not rare for people to dump problems onto unsuspecting future owners or for dealers to have no idea.

 

fortunately you were able to absorb that repair costs, many people don't plan on or can afford $1,000 bills right after purchasing.