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Old 06-25-2019, 12:05 PM   #1
fullmetal
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Default overheat at idle only after high RPM

**************PROBLEM CONTINUES PLEASE SEE BELOW*****************************

background 07 WRX, 205k miles timing belt done 2500 miles ago, new fail safe thermostat, new water pump (dayco kit), full oil, full coolant, blows hot, plugs replaced for factory at 160k

So as the title says, if I drive on the highway then come to a stop, toll booth, coast for a mile etc the car starts to over heat until I bring the RPMs back up. It can idle all day, cruise, run back roads and no problems at all. I am at a loss for whats going on. It will heat up to 2/3 mark on the gauge then stay there and slowly (very slowly) come back down to about 1/2 way and stay there. I have a CEL on that is normally a very small evap leak, I am going to pull the code today and see if there is anything else but I know the last time it was that and a bank 1 lean code.

Checked the coolant it was about 1 cup low so I topped that off, checked the oil it was a Qt low (first time I've ever seen it low) so I topped that off. Both are holding fine for the last 100 miles since. No indication that the head gasket is blown (mixed fluids, smoke, etc)

aAny one have any ideas? I'm at a total loss here
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Last edited by fullmetal; 08-09-2019 at 12:04 PM.
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Old 06-25-2019, 06:24 PM   #2
MortonCharbo
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What about your radiator fans and the associated fuses and relays?
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Old 06-25-2019, 07:34 PM   #3
fullmetal
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fan runs fine. And one of the over heats was coasting from 70 down to 45 and I have to imagine the airflow through the radiator at that speed is more than what the fan would flow anyway
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Old 06-25-2019, 10:09 PM   #4
Blktrax
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Its not an OEM thermostat. Just went through this with my 02. Would warm up , gauge read 1/2 (normal) but I would park and sit and the fans would never shut off . Watched the data coolant temp was 215-220, would cool down to 205 , but the shut off point is 195f. So the fans ran low speed all the time. Swapped out the NON-OEM for the Subaru part, warms up to 205 and cools down to 192.

Also make sure you have your radiator caps in the correct locations if you have the 2, round in the radiator, wings on the surge tank on the intake.
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Old 06-26-2019, 01:32 PM   #5
fullmetal
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Rad caps are correct that was a good call though, I didn't know until I did the timing belt they weren't the same. I'll get a new thermostat today and do it this weekend, I had a thought that might have been it but I didn't want to start digging blindly either. Thanks for the advice I have a 450 mile drive next Monday I'll report back the results
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Old 06-26-2019, 11:02 PM   #6
stu
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Lifted a head! do you have to keep bleeding the system?
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Old 06-28-2019, 07:21 PM   #7
fullmetal
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nope heads are fine.

Blktrx I replaced the thermostat like you said and a 2 hour drive after had no issues at all good catch thanks for the suggestion.

My guess is that the one I had just restricted it too much so at idle it would over heat but at speed it could force enough coolant through to keep the temps down. Weird
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Old 07-01-2019, 09:19 PM   #8
stu
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Report back when it overheats again.
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Old 08-09-2019, 12:10 PM   #9
fullmetal
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*************UPDATE THE PROBLEM CONTINUES**********************

I don't know if this is related or something else and I am again at a total loss.

I replaced the thermostat as suggested and with the exception of a weird process burping (the car randomly pushed out a lot of the coolant when I was almost done through the turbo overflow tank) which I simply attributed to a trapped air bubble that I had missed. I drove the car for a week with no issues (about 500 miles)

Then 2 hours into a drive to NC on 695 near DC (4 lanes divided each side with heavy traffic) the car starts to over heat. I get it off the road and it boils all the coolant out of the (not turbo) overflow tank. I had all the coolant still in the car from replacing the thermostat the previous week and since it was only about 2k old I used it to refill the coolant to try and get off the highway to a friends house 20 minutes away. I got there, let the car cool, burped it more thoroughly with it starting to hint at overheating only once. I decided to carry on my drive to NC thinking if its going to over heat again at least I'm closer to the destination because I was catching a flight from there in 2 days.

Car drove fine with no issues for another 1000-1500 miles. Then Sunday it overheated and poured all the coolant out of the overflow again after driving 3 hours, idling for 5 minutes while paying for parking, then driving .1 miles to a parking spot. It over heated as I parked. I let it cool, refilled the coolant to get to my friends house on the other side of philly, I checked it out and the car was fine. I couldn't figure out why it again over heated. I drove it for another 500 miles deciding that I would check it every day or two and see if I could notice low coolant, sweet smelling exhaust, exhaust smell in coolant, anything. Nothing. Today it overheated again and dumped more coolant out. So stuck on the side of road I added coolant after it cooled some. I was able to drive back to my apartment (15 minutes) no issues at all.

Every time it over heats suddenly, all at different speeds and conditions but never at idle. It dumps the coolant out of the over flow with no other indications of leaks. I add coolant back and it runs like nothing ever happened. I check it every few days and see no lack of coolant in between over heats or anything else.

Any ideas from those more intelligent than I?
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Old 08-09-2019, 12:34 PM   #10
Jedi03
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check actual coolant dilution with test kit...how did you verify heads are good?
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Old 08-09-2019, 07:32 PM   #11
Blktrax
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Coolant is able to operate over 212f due to it being under pressure. However if coolant is being pushed out of the system, the only way for that to happen is being replaced with volume of air, or a sudden venting of pressure. i.e. what happens when a cap is removed hot, and you get the geyser of coolant to the face.

With that many overheat cycles, the heads need to come off and be inspected. Besides the typical gasket failure or possible cracks around the spark plugs into the coolant jacket and combustion pressure making it way into the coolant. You wont always get a smell or a visible leak, but usually you will see near constant small bubbles in the over flow tank

Unless something is routed incorrectly or one for the rad hoses is collapsing. Its pretty much going to be head gaskets or heads.
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Old 08-10-2019, 11:22 PM   #12
Theorifice
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This sounds very likely to be a head gasket issue resulting in leaks from combustion pressure causing exhaust gases to enter the coolant chamber. The head gasket probably seals ok when cold but one you get warmed up and driving, exhaust enters the coolant.

During normal driving, the water pump is moving coolant around enough to be effective at cooling. When you're idle, coolant isn't moving much through the system and the air in the system causes your engine to overheat.

205k miles is about the time you'll need to do the head gaskets.
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Old 08-13-2019, 06:18 PM   #13
fullmetal
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I am with you guys at this point there has to be a leak at the head gasket/head. Well guess I have to decide if its worth fixing now.
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