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Yes, Another Subaru Overheating - At Wit's End

OK experts, I have tried to get this posted three times now, but never see it in print…
I have a 2001 Subaru Outback Limited with 135K miles on it. In the last year, I had two complete head jobs (the second because the new water pump failed while on the highway). In addition, I have had multiple water pumps, lots of thermostats and a new radiator installed. The last thermostat is an OEM. The car had been running fine for about a month and now overheats after about 30-40 minutes of combined, but mostly highway driving. At first, the gauge would rise to about 3/4 and then drop after about ten seconds, but now it goes to almost red and drops to 3/4. If I blast the heat, it will drop pretty fast. My mechanic told me that while diagnosing an earlier overheat issue (just before the good period), he noticed that the gauge would rise, but the computer temp would remain stable. He tried a new sensor, but said it made no difference, so he returned it. What is left to replace? I am sick of not trusting this car. HELP!!!

get rid oth this beast

The problem with overheating is that it can create a plethora of secondary problems. Someone is going to have to go through this from scratch, looking at the radiator’s flow rate and ability to evenly and effectively dissipate heat, evidence of a breech in a headgasket, fan operation, abaility of the system to hold sufficient pressure, and even water pump condition.

I’d try another shop.

“What is left to replace?”

The dash gauge.

And the radiator.
But I’d suggest a good analysis of all the parts of the system as well as the engine for headhasket breech before changing another part.

I have a feeling the folks who are fixing your car don’t completely know what they are doing. Subarus have their share of these problems, but they normally cease to be problems after a proper fix.

Your mileage is not that high, but like others, I believe the improper fix has led to some secondary problems, and you my have to send a lot of money to get everything right. As mentioned get a second opinion from a really qualified mechanic, preferably one who knows Subarus. Skip the dealer at this time because they will propose an extremely expensive fix whcih will likely not worthwhile.

To answer some questions, as I said before, the radiator is new, the water pump is new and the heads are resurfaced. The only possible link to the renewed overheating was a jarring pothole I hit. (Although unlikely) The gauge began to go up within about ten seconds of that, but still takes 30 - 40 minutes to begin to rise from cold start.

Now that we know about the pothole, I’d suggest an immediate check for damage to the radiator, fan, water pump, and maybe even the oil pan. Oil removes heat from the cylinder walls and the pickup screen for the oil pump is just above one of the bottom surfaces of the pan. It’s also possin;e that the bump caused the inner liner of a radiator hose to collapse, restricting the coolant flow.

Did you put in a new radiator cap with the new radiator?

At least you now made it into print. Sorry I don’t have an answer, but let me ask this. Are you losing coolant?

If anything, the reservoir is too full. There is no damage the crash pan and the pot hole was jarring, but not that deep. Radiator cap was new last year or the year before. I transferred most of the coolant back to the radiator with a turkey baster. The reservoir is at the “Full” line now. The cap did “hiss” when I took it off, despite the car being garaged most of the week. Perhaps the radiator cap is to blame as it would not seem to allow fluid back into the radiator.

I replaced the radiator cap with an OEM (the cheapest thing I could do), but it did not help (although there was no hiss on opening). I took it back to the shop and the mechanic discovered that my model (by manufacture date) uses the previous year’s thermostat. He replaced that. He told me that the temp is down, but there is still a pressure build up that he can’t figure out. He said that if it continues to overheat, it is probably the heads again and that, combined with “rod slap” tells him to ditch the car or engine. I took it to work this morning (30 highway miles) and only after twenty minutes did the gauge rise. It never went above 3/4 and would come back down. I did notice that it would rise on long uphill climbs and occasionally short steep hills. I also noted yesterday after a 20 minute drive (and rising gauge) that the bottom coolant hose is cool to the touch as is the lower radiator. Is the radiator that efficient?

The hiss on opening the radiator cap after the engine has been cool for a while often indicates a head gasket issue, since it is often caused by the exhaust gases are entering the cooling system through the head gasket. I would assume they replaced that they replaced the head gaskets and checked to make sure the heads were not warped during the “complete head jobs”.

I’m not familiar with the Subaru engine in particular, but perhaps the block is stripped and the head bolts are pulling out of the block. I would hope that they would have noticed that when working with the heads earlier, though.