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Ask Mike V. Your Own Question
Mike V.
Mike V., Subaru Technician
Category: Subaru
Satisfied Customers: 23610
Experience:  Certified Subaru Technician, factory trained by Subaru.
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overheating occurs not in idle mode but when driving

Customer Question

overheating occurs not in idle mode but when driving
Submitted: 4 years ago.
Category: Subaru
Expert:  Mike V. replied 4 years ago.
Welcome to JA! I am Carguy1 and I will assist you today.
Hi there!
Is this a 2.2L engine or 2.5L?
Customer: replied 4 years ago.
this is an 2.2
Expert:  Mike V. replied 4 years ago.
Ok, it's not common for the head gaskets to leak on the 2.2L
Do you notice any loss of coolant or maybe even heat inside the car during any of the time you drive it?
Is the coolant actually boiling out of the overflow?
Lastly, how long can you drive it before it over heats?
Customer: replied 4 years ago.
ok. here are the issues that occurred before and after all cooling system parts were replaced:

and yes I spend lots of time to fill the system with coolant and the bleed the air out.
-you can drive for about 15 min before things the engine gets hot.
-at first there is heat in the car when the heater and fan is turned on telling me - ok the cooling system is working.
-then, under load on a hill this changes into no more heat transferred to the car heating system - no heat gets to the inside of the car. instead the coolant overheats and evaporates. there is coolant steam coming out of he car only when its overheating. those leaks are not detectable when the coolant is in liquid form.
-also, often the coolant is being rejected into the reservoir/tank

Expert:  Mike V. replied 4 years ago.
Where or what general location do you see the steam?
Customer: replied 4 years ago.
steam is coming out of the motor block.
first I thought, the radiator might be leaking and I replaced it and the hoses. still steam.
it's really hard tell where exactly the steam is coming out.
I made an effort to really tie down the hose connections between radiator and engine.
Expert:  Mike V. replied 4 years ago.
Ok, if it is coming out of the block, it may be the O rings for the cross over pipe. This is really pretty rare, but I chased one around for a long time before I found it. It didn't even show up with a pressure test.
The car is sucking in air some place, this is why the heater stops working, it fills with air, then starts the overheating process.
The crossover is where the coolant temp sensor is located under the intake manifold.
I would also take a look at the hoses on the driver side that go to the heater core. At least the clamps and make sure it's not leaking there.
I just don't have a good diagram of the crossover pipe to show you.
Customer: replied 4 years ago.
Sorry it took a while to get back to you.
I have tried several mechanic shops in town and had some diagnostics done.
According to professional mechanics, the O-rings on the cross-over pipe seemed to be ok and not leaking.
What was found to be the reason for overheating were two issues.
1. Radiator eventhough is was replaced 3 weeks ago, it was leaking at higher temperatures - replaced radiator again. - this stopped 75% of the overheating problem.
2. Cylinder heads were found to be ok during head gasket replacement but were not send to a machine shop for verification - this could cause the remaining 25% of overheating problem that can occur from time to time on a very steep hill
Expert:  Mike V. replied 4 years ago.
Yes, if the heads were not planed, or checked it is very possible.
Who would have thought the radiator would cause the problem?
Sorry to hear it all but glad to hear you are on the right path.
They could do a combustion test and see if the exhaust is getting into the coolant.
This would tell them if the head gaskets are bad.