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Temp Rise After Long Drive

2K views 12 replies 7 participants last post by  traildogck 
#1 ·
Hello All,


I'm having what I think is a peculiar cooling system issue, and thought I would run it by folks here first before I take my car in.


Two weekends ago, two hour drive up to the mountains from Denver. I slow only twice after getting on interstate, once to get something to drink (place closed, so never turn off car) and then when I arrive. Both times engine temp climbs to near 3/4. Fans are both running, so I think maybe its the thermostat. Since I don't know the thermostat's history, I change it.


This past weekend, make the same drive. Same thing happens. I get to the mountains and slow through town, temp rises. I let the car sit overnight. Next morning I look under the hood and see that the reservoir tank is full (not at the full mark, but FULL to the brim). I check the fill tank, and it looks empty. I thought maybe I hadn't quite got all the air out, so used a turkey baster to transfer coolant to the fill tank. When it was full the reservoir tank was about 1/2" below the full mark.


Drove home. No problems on the drive, so I let the car idle a bit when I arrive. Temp starts to rise.


Radiator, hoses, and water pump replaced within the last few years. Thermostat replaced week. Fans both run. Both radiator caps are new. Temps seem normal just running around town.


Anyone have any ideas what my problem might be? Why would coolant expand to the reservoir, but not return when cool? Did I do something really stupid somewhere here? Thanks!
 
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#3 ·
Thermostat replaced week.
Did you get the thermostat from the dealer? There are many aftermarket thermostats that fit this car, but none work as well as the real thing from Subaru.

Both radiator caps are new.
Confirm- the one with the grip wings goes on the tank, the plain round one is on the rad.

Why would coolant expand to the reservoir, but not return when cool?
Check the hose that goes from the radiator neck into the reservoir. Sometimes during cool-down, that hose will suction itself to the bottom of the reservoir instead of transferring coolant back into the system. You can eliminate this by slicing the end of that hose at a 45° angle with a razor.

Head gaskets almost never fail in turbocharged Outbacks, even though it is quite common in the non-turbo models.
 
#4 ·
Did you get the thermostat from the dealer? There are many aftermarket thermostats that fit this car, but none work as well as the real thing from Subaru.
From the dealer. And seriously, somebody thinks its worthwhile to go to the trouble of making an aftermarket one? Its only like $20!

Confirm- the one with the grip wings goes on the tank, the plain round one is on the rad.
That is how they are arranged. The original tank one was missing its label, which is why I went ahead and replaced both - cheapish insurance.

Check the hose that goes from the radiator neck into the reservoir. Sometimes during cool-down, that hose will suction itself to the bottom of the reservoir instead of transferring coolant back into the system. You can eliminate this by slicing the end of that hose at a 45° angle with a razor.
Will check that tonight, thanks for the tip!

Head gaskets almost never fail in turbocharged Outbacks, even though it is quite common in the non-turbo models.
(fingers crossed!)
 
#7 ·
I also hate to say it, but it sounds like a small head gasket leak. My wife's 04 was constantly running low on water, but drove fine. Only ever started overheating once the water got low enough. Well after 9 months of that I finally put head gaskets in it. And it's fixed. I tried, thermostats, radiator, hoses, clamps, etc. I did a block test with the color changing liquid. I also did overnight cooling system pressure tests and those did show that I did indeed have a leak. But I'd only drop 2-3 psi overnight. Now it did get slightly better after using some Subaru coolant conditioner. When I was still investigating. I wonder if left in long enough the leak was small enough it might have been fine for long time. For the first 6 months or so I added coolant every 2 weeks. But towards the end it was more frequently and any longer 1hr plus trips caused issues.

Good luck and lets hope it's something simple!
 
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