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Mike V.
Mike V., Subaru Technician
Category: Subaru
Satisfied Customers: 25677
Experience:  Certified Subaru Technician, factory trained by Subaru.
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I'll try to be as quick and detailed as possible. I have a

Customer Question

I'll try to be as quick and detailed as possible. I have a 2003 Subaru Baja that overheats. I had the same problem a year ago when it would overheat as well. replaced everything on the engine it could have possibly been. finally blew the engine. bought a new(rebuilt) engine where it was completely rebuilt. new gaskets, water pump, timing etc. 1 year later same identical problem. no leaks anywhere. radiator is new as well. biggest noticible problem is top radiator hose is hot and bottom one is ice cold. no flow through the radiator?? exactly the same problem as the last engine which scares me because I just dropped $4200 into this engine 1 year ago. sounds like thermostat not opening, but it is one year old too. read posts online everywhere and got no definitive answers.
Submitted: 1 year ago.
Category: Subaru
Expert:  Mike V. replied 1 year ago.

Hi there,

The very first thing I would do is replace the thermostat. This is a very inexpensive part and can very likely be the problem. Even though the symptoms are the same, it doesn't mean the same problem is occurring. For the record though, I do totally understand your concern.

If the thermostat doesn't resolve the issue, then you may be looking at a head gasket problem. New engine or not, it can be happening. If you have a warranty hopefully it will cover it. A combustion test will need to be done to see if there is any exhaust gas in the coolant.

It does sound like a bad thermostat, so I would start there.

Also, make sure the cooling fans are both going when the engine is hot.

Please let me know what more I can do to assist you today. Also, please remember to rate my answer, Just Answer does not compensate me for my time and resources. Follow up questions are included in the price of your question. If you are using the free trial, or have a subscription a rating is still required.
Thank you so much!

Customer: replied 1 year ago.
I'm leaning towards it being the thermostat. But the last engine I had had the same problems. I replaced the thermostat twice. And it still overheated several times. I took the car to a Subaru dealer and they did a complete inspection of the engine. They said everything was fine. Cost me $400 for the inspection. A week later it overheated and blew the engine. The lower hose was still cold when the engine blew. That's why I don't believe it's a gasket issue. I wish that if the problem is unfixable someone would tell me. I got that impression last year at the Subaru dealer.
Expert:  Mike V. replied 1 year ago.

On these cars, when the head gasket fails, it allows the exhaust into the cooling system. This overheats the engine so fast that the thermostat can't open fast enough to get the hot coolant into the radiator. This is why one hose is hot and the other is cold. The same as the thermostat going bad. If you replace it, and it doesn't solve the problem, it's likely the head gasket. A combustion test will prove that. They should have done that when they had your car before.

Customer: replied 1 year ago.
Well I'll start with the thermostat, if it doesn't fix the problem, I'll deal with that then. Thanks
Expert:  Mike V. replied 1 year ago.

You're very welcome, please let me know if there is more I can do to help out.

Also, please remember to rate my answer.

Thanks so much!

Customer: replied 1 year ago.
One mor thing, if it is a bad head gasket. Wouldn't that cause the engine coolant to heat up faster and therefore make the thermostat open?? It seems like if there was a leak in the head gasket the coolant would still circulate normally.
Expert:  Mike V. replied 1 year ago.

No, as I explained, it heats up from the 1500 degree exhaust gas so fast the thermostat doesn't open before the car overheats.

I personally think you have a bad thermostat to be completely honest here. This type of head gasket issue on this particular engine isn't very common. Usually they leak externally at the rear driver side head.

Customer: replied 1 year ago.
I was hoping it was the thermostat, but I felt the housing that holds the thermostat when it overheated and it felt cool(ish). I will try thermostat first as it is the least expensive option to start.
Expert:  Mike V. replied 1 year ago.

I am hoping it's the thermostat as well. I know the head gaskets aren't cheap to do, so hoping you have some warranty on this engine if it is in fact the problem. The thermostat will stop the coolant from transferring into the radiator as well, so it may feel cool. Remember, it's the coolant in the engine that's overheating, not the radiator.

Customer: replied 1 year ago.
Well, I replaced the thermostat and the radiator fluid as well. Same problem. Car overheaded when driving. It maintained an ok temp in park but it is 15 degrees out here. Again, the top hose had pressure in it and was warm. I was able to reach the bottom hose and it was ice cold as well as the housing that holds the thermostat. So that tells me the fluid in the enging isn't getting circulated, right?? The gauge says it's way above the red Mark but the bottom of the engine where the thermostat is is cool to the touch. I let it get real hot and then put it in park while idling for 10 minutes. Temp was stable but bottom of engine still cool. Further thoughts??
Expert:  Mike V. replied 1 year ago.

Do the combustion test, you have a bad head gasket sorry to say.

Again, the hot exhaust is heating the coolant before the thermostat can open. Take the thermostat out of the car, then it will flow freely and less chance of it overheating because at least then the coolant can make it to the radiator. I know you don't want to hear the head gasket is the problem. I totally get that, but throwing parts you don''t need is only going to cost you money that you could put towards repairing the head gasket. I have been down this road with these cars so many times, I have seen it time and time again.

Customer: replied 1 year ago.
Yeah this sucks. My question now is, if the fluid is getting heated by the exhaust, and is getting so hot. I let the car idle when the temp gauge was almost near the red for 10 minutes. Wouldn't the hot fluid have circulated through the engine down to where the thermostat is??? The car idled for 10 minutes while super hot
Expert:  Mike V. replied 1 year ago.

No, I have left them idle for an hour in the bay and never showed a problem, then take it for a drive for 3 miles and its overheating. I have also had some that people got mad because they said it was overheating and I couldn't get it to!!

Then drive it 25 miles and bam! Overheat.

This is why I suggest the combustion test. It's a chemical test that shows the hydrocarbons if they are in the coolant. Another thing, you clearly know what the coolant smells like since you have been working with it. If it smells acidy and not sweet, it's another indicator. I don't recommend it as the "main" test, but sometimes you can tell by the smell. I assume the cooling fans are kicking on when it's hot?

Customer: replied 1 year ago.
Fans are working fine. I just try to understand the inner workings of the engine. To me logic dictates hot fluid should be circulated. Car is in too good of shape to trash so I guess I'll have it tested for head gasket
Expert:  Mike V. replied 1 year ago.

Being a Subaru there isnt a lot of logic on the head gasket issue.

please be sure to let me know if there is more I can do to help.

Also, please remember to rate my answer.

Thanks so much