Overheating on mountain roads

I have a 2002 Subaru Outback that has started overheating only when I try to go up into the mountains. It starts within a few miles of starting up a steep grade and cools down the instant you start down the mountain. I have had no problems with regular driving conditions. The only pertinent info might be that it did have a coolant leak last summer and overheated then. Thanks for the help.

You may have an air bubble in the system that causes the thermosensor to not be immersed in coolant when you’re under an incline. An airbubble is never good because it means that the car cannot efficiently cool itself but in this cause it is even worse because it actually causes the fans to not come on.

Try this on the car once is has cooled off and you can touch the radiator:
Park it on a slight incline or ramp, take the radiator cap off and start the car. Add some coolant once in a while and observe what it is doing. Rev the engine up and down some.
You’ll note a large air bubble burp out once in a while. When you do, add more coolant until the burping stops. Close off the radiator and try driving it again.
Most cars have a burping valve on top of the engine but Subaru does not.

Subarus especially are kinda picky when they are refilled with coolant. If you had a leak, it may not have been fully filled. Often it is best park it on ramps, to take the top radiator hose off the radiator, leaving the other end onto the engine and stick a funnel into it to fill the engine up first. Then when done, very quickly, push it back onto the radiator.
That tends to minimize air bubbles.

I think your cooling system is showing it needs attention soon or you will start noticing a problem eventually in normal driving. Here is my advice:

Replace the radiator cap and see if it gets any better. It’s relatively cheap to try this. (My Civic recently had air in the radiator and the overflow tank was overfilled. Replacing the radiator cap solved the problem.)

If it doesn’t get better, have the cooling system pressure tested.

If the pressure test doesn’t show any problems, have the radiator flow tested. It might have clogged passages even though coolant can still flow through it, keeping the coolant from being cooled adequately.

If everything checks out, replace the radiator anyway. A partially clogged radiator can be really hard to diagnose.

I agree with Whitey. Driving up mountain roads places higher demands on your cooling system. I suspect it may end up being your radiator not able to dissipate the heat as it used to. But I’d first try the steps Whitey and RemcoW recommended.

I’d take it to a radiator shop and have them test it. They might find an air pocket and know how to bleed it properly.

I think the problem is more likely to be a clogged radiator. I have a 4x4 truck that had this same problem. They did some kind of pressure test with the radiator installed and determined it was clogged. The radiator shop removed the radiator, put it in some kind of cleaning tank, re-installed it in the 4x4, and the overheating problem was fixed. Simple as that. And not overly expensive. They said the radiator’s passages was just clogged from calcium deposits.

Overheating while going uphill is the classic symptom of a radiator cap that is not holding pressure. Replacements are cheap so start there.

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Other than the engine coolant related causes that are mentioned some other possibilities could be an inoperative cooling fan or fans, bug clogged condenser/radiator, excessively high A/C head pressure, or even partially clogged catalytic converters, etc, etc.

Just something for consideration if all else fails.

Agree with GeorgeSanJose; a dirty or partially clogged radiator is the most LIKELY cause of such overheating if other wise the system works OK. Have it checked out by a specialty shop, which will check the thermostat, the cooling fan as well as the health of the rad.

The service intervals for modern rads are too long; many are 100,000 miles. On a typical Ford, and many other cars, that would be the life of the radiator.

also take the car out overdrive the extra rppms will help to move more water in the coolen system and less strees climbing the grade

Keith NAILED it. He posted about uphill overheating being the radiator cap in 2009, and twice in 2012 that I found on these forums. My 2004 Jeep WJ w/ the 4.0 was overheating going uphill. Research was showing everything from a clogged radiator to a blown head gasket. I was dreading replacing my radiator in my driveway but decided to buy a Gates radiator cap for $10. Immediately fixed the overheating issue under load. Wow. The overheating ruined part of my vacation in the mountains of Vermont and there was a damn Advance right down the road!! THANK YOU KEITH!! 190k on the motor and still going strong.

You’re welcome.

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