Overheating On Highway

[NormVad]

I’ve got a frustrating overheating problem that I haven’t been able to resolve yet…. Here are the details, any insight would be GREATLY appreciated!

2001 Outback 2.5. Recently replaced head gaskets, timing belt, water pump, thermostat, radiator cap, upper and lower hoses. Thermostat and radiator cap are both Subaru. Head gaskets were replaced because they were leaking oil. It runs fine except will run very hot at high RPMs, usually when driving on the highway. Can drive all day on back roads, no issues. When it’s heating up you can turn the heat on full and it will keep them temp at a reasonable level. Sometimes if you turn the heat off then back on a moment later, air is cool. Not freezing, not hot. When this happens, temp goes way up. Pull over, turn the engine off for 30 seconds – 1 minute, start back up, turn the heat on, it is ok and the temp stabilizes. No leaks, no smell that I’ve noticed. I did notice when its running at a high temp the overflow fills right up but doesn’t overflow, just close. One you are off the highway and the temp is back to normal you can drive all day, no issues.

Exhaust leaking into coolant? Blockage in the radiator? Too much water in system vs coolant in the system? Air? I have burped the system.

I was going to test for the exhaust leaking and clean off the radiator (just in case) this weekend.

Any other ideas?

Thanks!

[AWDFTW]

Are the fans coming on properly?

[1 Lucky Texan]

who did the work listed?

air or 'gas' seems to be pushing coolant into the o'flo. If you can see bubbles in the radiator while idling, you are a good candidate for the chemical HG test as sold at autoparts stores. It is a tube with a liquid in it that will change color when gas from the radiator is pulled through. Results are iffy when no bubbling is present though, and often Subaru gaskets only fail at speed/under load.

one could argue though, if you see bubbles whle idling, where else could that gas come from? (localized boiling maybe?)

when the system cools, does it pull the coolant back in from the o'flo tank?

[NormVad]

Yes, fans come on and stay on while its running hot.

I did all the work.

When the system cools the coolant is drawn back. I'm not loosing any coolant.... very strange.

When I bled the system, I was seeing some bubbles but, if I remember correctly, they stopped at some point. I let the car run about 20 minutes with the cap off to bleed it.

[cmill1154]

Originally Posted by NormVad

[SIZE=3][FONT=Calibri]Sometimes if you turn the heat off then back on a moment later, air is cool. Not freezing, not hot. When this happens, temp goes way up. Pull over, turn the engine off for 30 seconds – 1 minute, start back up, turn the heat on, it is ok and the temp stabilizes.

This reads like there is either a huge air bubble in the system and gets stuck in the heater core occasionally or the core is clogged.

[1 Lucky Texan]

you could check the coolant system vaolume listed in the manual, then see if that precise amount can be drained out. If less, you had a 'bubble' of air/gas.

also, just doublechecking but, the t'stat was from the dealer, installed with the return spring up and jiggle pin forward? Anyway, you could pull it , put in a pan of hotwater on the stove, check with therm to see if it opens at 170* F.

[NormVad]

Yes, I picked up the tstat at the dealer and it is installed in the correct direction... I originally picked up the non-oem tstat but changed it out just to be sure.

Something I left out in my original post was before I changed the HG I had used a sealer for a temp fix until I could get the HG done... hmmm, maybe thats creating a clog somewhere?

[canubaru]

Something I left out in my original post was before I changed the HG I had used a sealer for a temp fix until I could get the HG done... hmmm, maybe thats creating a clog somewhere?

if you did not flush the cooling system when you drained it that could easily be the issue. that stuff, some of them any way, do not dry and clog until it reaches the air. so a system with sealer in ti left open to the air will dry and harden. and maybe in places you don't want it to.

back flush the heater hoses and core and flush the rad. it should flow out the bottom of the rad as fast as you can put it in the top with a garden hose.

[NormVad]

Another interesting development today from the ride home... most of my ride is highway so I put the heat on as soon as I got on. About 10 minutes in, started to run hot even with the heat on so I decided to take the back-roads so as not to risk over heating. I left the heat on and a few minutes later the temp was back to normal. When I stopped at an intersection I noticed almost immediately the temp started to go back up and the heat cooled off. As soon as I started back up everything was back to normal. Just another piece to the puzzle.

[dryvby]

Did the temperature swing like this prior to the work? It does seem like a head gasket failure.