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I am assuming that I have the very fun HG issue, but figured I could describe my issue and see if anyone thinks it could be something else.

My car was sitting through a storm for about 5 days (car did not flood), and the first time I drove after the storm it I noticed that it would run slightly hot at highway speeds, then overheat when stopped/slow. The issue was sudden, as the last time I drove before that it the needle stayed right below halfway.

The car has 140k miles on it, and had the thermostat (not OEM), water pump, timing belt, and plugs replaced at 100k with a coolant flush at 120k at a Subaru dealer.

When I drive the car in town it will run slightly hot (right above middle) and get slightly hotter when I bring it on the freeway. However, as soon as I slow from a highway speed to about 5-15mph in traffic it will overheat. I pulled over and let the car cool for about 15 minutes and turned it back on. The gauge returned to the middle and did not budge driving 20mph back home for about 10 more miles.

I opened the radiator and noticed that the coolant level was down a couple inches in the radiator and the overflow was between the full and low level. The oil seems good and the coolant in the overflow is somewhat brown due to the additive I believe. I don't see any leakage on the ground and the external HG's dont show any signs of leaking.

I ran the car idle on level ground with the rad cap off, and noticed that it would have a couple bubbles about 5 minutes apart when the engine got to temp. I filled up the overflow and radiator and drove it around until the engine was starting to slightly overheat. I got out and looked in teh overflow and didn't notice any bubbles. However, when I asked a friend to hold at 3,000 rpm I could notice bubbles in the overflow. Both fans run when the AC is on.

I bought a new thermostat (OEM) and rad cap which I plan to replace this week, but was curious if anyone had any other thoughts.

I appreciate all of your feedback and thoughts on this issue.
 

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Your non OEM thermostat may have encouraged your HG to fail. The non OEM tstats are well known for causing overheat issues - continuing to run the car hot pretty much is a 100% promise you will blow a HG with any car today.

Get the new tstat and cap on the car - burp it ie let it idle for a while with cap off and top off the coolant.

Check the over flow hose for cracks which will cause the car to draw air instead of coolant. And see how it goes. DO NOT RUN IT HOT!

Also possible that the fans have failed and are contributing to this issue. Turn AC on both fans should run - if not you probably have a failed fan causing a problem also.
 

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my first thought was maybe a fan not working or they don't kick to high speed(given the storm issue - check for debris on/around the radiator and fans), but there should not be bubbling as you describe so, yeah, likely HGs. You can try the chemical test available at the car parts store - there's a youtube video (probably several) that show how it works.

be prepared for bad news.
 

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Discussion Starter #4
I will take a look at the chemical test and see what the results are. I thought this phase engine did not have the troubles of an internal gasket leak, or is the issue just "better" than the old phase 1 engine?

The engine only ever got to the top red bar one time, and all of the other times I shut it down when it raises slightly above halfway as the normal position is just below half.

Both fans run when the AC is on, but I could never get the fans to run while the car was running idle and AC off. The engine would get up to temp and level off without the fans ever coming on.

If there is air in the system, would it be normal to see bubbles in the overflow @ 3,000rpm or would that condition only be caused by constant air/gas getting into the system somewhere? I called SOA and my VIN was not covered under the extended warranty so even though I have all my records of maintenance they will not offer to help.

As a curiosity question, would you consider "running the car hot" when the needle is just above half way? Or is "running hot" only considered when it is near the red?
 

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For the external HG failure the chemical test will not show anything.

The visual check driver side bottom back corner of the engine is generally where people will see coolant dripping off the block / head onto the hot exhaust. Run the car for a little bit - shut it down with tires cranked to the right. look under the car from just behind driver side front wheel looking forward you will see the bottom driver side rear corner of the engine where the coolant will drip off onto the hot exhaust. This is the text book external HG failure. Mine did this at 65K - no over heat I spotted the issue long before it reached that point. Subaru pulled the head tossed an updated multi layer gasket on and the car was perfectly fine from 65K to 180,000 miles when I sold it with no issues. I needed a larger car.
 

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I suppose if the system cooled and the inflow of air from the leak were easier than pulling fluid back through the rad cap - yeah.

but at temp and pressured up, seems unlikely it could generate a constant stream of bubbles. The combustion chamber can.
 

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Does an external leak show bubbles in the overflow when running?
Yes - when the system cools and draws air back in due to empty over flow bottle or as I said cracked hose or leaky cap allowing it to draw air vs coolant.

The 2002's were more known for external leaks vs internal combustion chamber failure which is why even up through 2009 the chemical test in most cases never shows any HG issues unless the car was beat to **** and someone actually found a way to blow the HG internally to the combustion chamber.

The very early 98 2.5s had internal failures as did the old 2.2 in the early 90's its pretty rare to see them with internal failures after 2000.
 
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