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2004 Forester XT
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2 Posts
Discussion Starter · #1 ·
Howdy! I have an '04 XT (150,000 miles) and I've recently been experiencing some overheating issues on inclines. I've never owned a turbocharged vehicle before, so my question is, is this normal? I live in Denver and within about ten minutes of hopping on I-70 passed Golden the needle starts creeping on me. I've also had issues overheating going about 85 mph in 80 degree heat outside of Vegas, granted that was after nearly twelve hours of driving. Both radiator fans kick in when it reaches temp and I've so far had no problems with overheating during 30-45 min city commutes in 90+ degree temps. There are no visible leaks and no coolant smells. Does the stock radiator simply lack the cooling capacity to handle driving at altitude on an incline or should I be looking for something to fix? I've been looking at Mishimoto and Koyorad radiators, but if there's an issue with my cooling system, there's no guarantee replacing the stock radiator with a better one will actually fix my overheating issue... Thanks in advance, I'm a bit of a noob when it comes to car stuffs!
 

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2012 SH Manual Diesel
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737 Posts
Start with the cheapest and easiest potential causes first.

How old is the radiator cap? Is it genuine Subaru, and the exact cap for your model? A worn out, or incorrect radiator cap, is a sure cause for overheating symptoms. You can test the cap (e.g. Mityvac radiator test kit, or ask a radiator shop), to see if it is holding the correct pressure, and for sufficient duration. However, if its old or the history is unkown, it may be a good idea to replace it anyway. And also pressure test cooling system.

When replacing the Radiator cap (or thermostat), I'd recommend using Genuine Subaru, and absolute correct one for your engine and model. You must also purge any air in the system; which develops with localised boiling of engine coolant, in hotspots in the engine. This occurs, when the radiator cap can't hold pressure; and the reduction in cooling system pressure, also reduces the boiling temperature of the coolant.

The purging can be a pain in the neck; because, when you think you have all the air out, there's still some air trapped in there. So long as you have air trapped in the system, it again won't pressurise correctly. Any air can also lead to oxidisation in the cooling system (inparticularly the thermostat), which adds to the overheating symptoms. If this scenario occurs, it can make people feel, that they can't seem to diagnose the overheating issue, and that the radiator cap, didn't solve the problem.

Consider trying the cap first, with air purge (or coolant flush, if its due). Check to see if overheat symptoms remain, then go from there.

Let us know the condition, colour or contamination of both your engine coolant, and also engine oil. These may indicate, other major causes. Do you have to top up your coolant level at all?

Is the radiator clear from obstruction, with good air flow, and are most of the fins straight (to allow good airflow, and surface area).

How is the engine running (power, torque, efficiency, starting, smooth idle, misfire etc)? are there any engine tune or maintenance issues that could cause the engine to run hot (e.g. lean AFR, boost control issues etc).
 
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