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Hey all, this may be a book, but bear with me. I've read all the info I can find on the internet about overheating foresters, can't seem to fix it. Lets start from the top.

Bought my Subaru 6 months ago in Montana, ran great, temp gauge never moved over the half way point. Most of my driving was quick 1 mile trip to work and back, although we did a camp trip to Glacier pulling a boat (gauge still never went over half).

A month ago, I took it in to have front brake pads replaced and I noticed a little bit of coolant clinging to bottom of thermostat enclosure. Figured it was a leaky seal, so I told the mechanics to replace seal. They ended up putting a new thermostat in it (I don't remember if they said it didn't have a thermostat in it already and they just swapped it for some reason). I didn't think to ask them why they put a new thermostat in it (probably didn't have one in).

Immediatly after they got done with it, I noticed my ScanGuage reading higher temps (198-224) after warmed up. The car temp gauge would be at the tick right before red line at 224. I was leaving from Montana to Texas that day and figured as long as it didn't go higher than 224 I would be ok. During the 1700 mile drive, temp fluctuated between 198-224 just as before. I noticed that while driving, if temp guage was over 220, I would floor it and immediatly the temp would go down to 198 (I think the RPM's shooting up increased the water pressure enough to open thermostat). Of course, when I resumed my cruise, the water temp start creeping back up again.

Made it to Texas with no other problems. Took it into the shop to see if maybe the new thermostat the mechanic in Montana put in was faulty. I swapped it with a brand new 170 stat. Test drove it and saw no difference---still running hot. I noticed that the upper hose was hot and the lower hose was cold. Top of radiator was hot and lower radiator was cold. I started to think it was a radiator blockage...so I did the stupid thing and went and bought new radiator. That didn't fix problem either---same symptoms. I then took it in to have it pressure tested. The ASE's said it held pressure fine. They also mentioned that the upper hose was sitting at around 160F and lower was around 106F--which is normal according to them. They said fans were working normal and they found no leaks. I told them my temp guage was reading 224 and they said Subarus run a little hotter than other cars---it's normal. (If 224 were normal the needle on the guage would be sitting in the middle, not 3/4 mark). After that, I called Subaru dealer to ask what normal operating temp is and they said "In the middle"---they wanted $98 to run diagnostic on it. I said no.

A little more details.....the system does not leak any coolant---it is always full in radiator and overflow evertime I check it. There is no water sounds coming from dash area. There are no coolant smells or burning smells inside cab. There is no frothy coolant inside radiator or overflow. No oily residue in overflow. No smoke blowing out back.

My theory is this, in Montana the mechanic installed a thermostat because there wasn't one in there. The dealer I bought the car from probably removed it to hide a cooling problem. I think the impeller on the waterpump is free spinning or there is a blockage in the engine or maybe even the temperature sensor is giving false readings. Not sure.

Need some help if anyone has had this issue. Sorry for the book!!
 

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2006 Forester XT
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That's why they don't put ccoolant temp gauges in cars anymore - all you get is an idiot light for 'too hot'.

You got a Scangauge, and it's now given you 'something to worry about', when in fact all is normal.......
 

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... Bought my Subaru 6 months ago in Montana, ran great, temp gauge never moved over the half way point... noticed a little bit of coolant clinging to bottom of thermostat enclosure. Figured it was a leaky seal, so I told the mechanics to replace seal. They ended up putting a new thermostat in it... Immediatly after they got done with it, I noticed my ScanGuage reading higher temps (198-224) after warmed up....
My theory is this, in Montana the mechanic installed a thermostat because there wasn't one in there. The dealer I bought the car from probably removed it to hide a cooling problem....
Cooling systems don't work without a thermostat, and it would be hard to remove one and patch the hoses back over the gap.

I don't think there is such a part as a thermostat seal. The first shop just replaced the thermostat. And it sounds like they didn't fill and burp the system properly. Air in the system might account for all your symptoms. Talk to the dealer about checking that.
 

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Discussion Starter #4
Cooling systems don't work without a thermostat, and it would be hard to remove one and patch the hoses back over the gap.

I don't think there is such a part as a thermostat seal. The first shop just replaced the thermostat. And it sounds like they didn't fill and burp the system properly. Air in the system might account for all your symptoms. Talk to the dealer about checking that.
There is a thermostat seal...actually a thermostat housing seal. I just put it on myself--so it does exist. Air in system is something I considered. I tried to burp it a couple times already....took rad cap off, turned heater on and let run at about 2,000 rpms. Maybe I'm doing it wrong, or maybe I didn't do it enough---I have no idea.
 

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Discussion Starter #5
That's why they don't put ccoolant temp gauges in cars anymore - all you get is an idiot light for 'too hot'.

You got a Scangauge, and it's now given you 'something to worry about', when in fact all is normal.......
Well, the factory gauge is reading one tick below hot and that corresponds with the temp on my scan guage....so. I don't use the scan guage as the end all be all, but it is helpful inconjunction with other tools. Hard to believe the factory guage reading that hot when the outside temp is 50F and it's raining, and hardly any load is on the vehicle. Everyone is accustomed to seeing where there guage normally lies on any given day. Now everday my guage is outside of the norm. Somewhere there's a problem.
 

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That's why they don't put ccoolant temp gauges in cars anymore - all you get is an idiot light for 'too hot'.
The needle gauge is telling him: "Too hot". The needle gauge stays in one place from 150F to 210F, so it's the same as an idiot light. And both of them really work well to tell you when it's "Too Hot".
... You got a Scangauge, and it's now given you 'something to worry about', when in fact all is normal.......
His ScanGauge says his coolant temp is over 210F, which is not normal. On a 100F day in city traffic with AC, my ScanGauge reaches only 210F before the fans knock it back down. That 210F is the max operating temperature. His temperature should not reach 224F on a road trip like it did. It should have stayed around 190F. I think he does have a problem -- the needle gauge shows it, and the ScanGauge details it.
 

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Discussion Starter #7
I should also note that the heater works excellent all the time. If I turn it on full blast when the scanguage is reading 224F, it will drop to around 216 after a couple minutes. I think that eliminates any notion of air or restriction in the heater core.
 

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Using oem Subaru thermostat or aftermarket brand? (There are reports that the latter, e.g. Stant, don't always work well in the Subaru cooling system cofiguration).

Is the t'stat installed so that the spring/sensor is toward the engine (and not toward the radiator)? (Subaru t'stats are longer and can go in only one way, whereas most aftermarkets are shorter and can be put in either way.)
 

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If you are pretty sure it's not air in the system, it's most likely the thermostat. Its probably not opening all the way as it should. I don't know what a new thermostat costs but if it's not too much I would source an OEM one from a reputable dealer and replace it yourself. Who knows what those goon mechanics installed.
 

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With the car up to normal operating temperature there shouldn't be a great difference in the heat of the top and bottom hoses if you are getting proper circulation. What stops circulation?. Either a faulty water pump, blocked radiator , faulty thermostat or air in the system. Assuming the water pump and radiator are ok that leaves air in the system or faulty thermostat. I would take the thermostat out and run the engine. Contrary to what has been said above the cooling system will work without the thermostat, it will just take a lot longer to get up to temperature. If the car now runs normally and stays cool then thermostat is problem. If not and still running hot then there is trapped air in the system.
 

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With the car up to normal operating temperature there shouldn't be a great difference in the heat of the top and bottom hoses if you are getting proper circulation. What stops circulation?. Either a faulty water pump, blocked radiator , faulty thermostat or air in the system. Assuming the water pump and radiator are ok that leaves air in the system or faulty thermostat. I would take the thermostat out and run the engine. Contrary to what has been said above the cooling system will work without the thermostat, it will just take a lot longer to get up to temperature. If the car now runs normally and stays cool then thermostat is problem. If not and still running hot then there is trapped air in the system.
you need a thermostat, otherwise you will never have system pressure, so at first your car slowly warm up, then the car will overheat becasue the system cant build pressure
 

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I should also note that the heater works excellent all the time. If I turn it on full blast when the scanguage is reading 224F, it will drop to around 216 after a couple minutes. I think that eliminates any notion of air or restriction in the heater core.
All the symptoms sound like the radiator itself is restricted internally. This severely limits its cooling capacity, but still allows pressure buildup and lack of coolant loss. You've replaced or checked everything else, so as unlikely as a partially plugged radiator might sound, there is not much left to try. Get a new rad!
 

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Discussion Starter #13
Ok guys, like I said before...I just replaced radiator----got the exact same outcome with brand new radiator. I focused my attention on the thermostat already....the one the mechanics installed was a Duralast 170 and it was installed correctly. I took it out and replaced it with another new Duralast 170...yes it is installed correctly. So changing thermostat didn't fix anything. I know some of you will say that the problem is still the thermostat because it isn't OEM, but I don't believe that. I've used bunches of aftermarket t-stats and I've never had a problem with any of them. I may go the route of running it without a thermostat---I think that will narrow it down to a flow problem. I'm stll thinking it is a water pump impeller free spinning or has messed up blades and is making less pressure than normal. But that is a fairly big job for me at the moment, I'm trying to disprove that it is the water pump. I appreciate all the replies.
 

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My apologies - I skimmed your first post and missed the part about the new rad.

Isn't it possible to measure the amount of coolant flow and pressure buildup while the engine is running? You could get a sense for whether or not there is enough.

As long as you are confident about the Duralast thermostat, let's run with your hypothesis as seen from these images of SOHC (water pump is on bottom right, you can see the thermostat housing - DOHC is similar:



As the water pump is run off the back (non-toothed) side of the timing belt, it is perhaps free to slip, although it looks like at least 90 degrees of the water pump pulley is in contact with the belt (and a bit more on the DOHC). Ages ago with my '88 Toyota Camry an independent mechanic told me that one failure mode with their water pumps (run the same way, off the timing belt) was a gradual seizing of the water pump pulley. This would eventually lead to overheating. So maybe this is possible in the Subaru as well. It might mean that a lot of friction would build up and cause premature wear on the belt, unless it was also coupled with slightly relaxed tensioners and maybe some grease on the back side of the belt.

So I'd say a partly seized water pump bearing.

Thoughts?
 

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... with my '88 Toyota Camry an independent mechanic told me that one failure mode with their water pumps (run the same way, off the timing belt) was a gradual seizing of the water pump pulley. This would eventually lead to overheating. So maybe this is possible in the Subaru as well. It might mean that a lot of friction would build up and cause premature wear on the belt, unless it was also coupled with slightly relaxed tensioners and maybe some grease on the back side of the belt. So I'd say a partly seized water pump bearing. Thoughts?
I think a bad pulley bearing would make noise, and when it seized, the pump would stop. The friction would soon destroy the belt and then the engine would stop with interference damage. Wally3430 said he took a 1700-mile trip. He could not have done that with a water pump pulley bearing about to seize.
 

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Discussion Starter #16
Wormguy---I tend to side with Vintage on this one. I don't think it would've lasted a 1700 mile drive. But, there is a very slight squeek coming from engine---especially when it's cold out. Not sure if that has anything to do with the problem. I've owned other cars that squeeked a little when it's cold out---no known problem with them. I'm thinking now that it could be a loose tensioner or bearing problem. Something that would make the impeller turn less. So, I what I'm going to do is get the hydrocarbo test done for the coolant---if that comes up clean I know it's not a head gasket problem. The only thing left really after that is to opener up and get into that water pump. I don't really think I have a choice now.
 

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you need a thermostat, otherwise you will never have system pressure, so at first your car slowly warm up, then the car will overheat becasue the system cant build pressure[/QUOTE

Coolant system pressure is supplied by the water pump. Sole reason for the thermostat is to regulate the flow of water through the radiator
 

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... Coolant system pressure is supplied by the water pump...
I thought the water pump just circulates the coolant, while the pressure comes from the hot coolant confined in a sealed pressurized system. When the engine is hot, and then stopped, the radiator cap cannot be safely removed. That pressure is not coming from the stopped water pump, but from the coolant explosively boiling when the pressure cap is removed.
 

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These are sealed cooling systems to allow the coolant to reach a higher temperature without boiling by running under pressure. Doesn't get away from the fact that the system will operate fine without a thermostat although will run cold most of the time. My Point originally was if the thermostat is removed then the car will not overheat if everything else in the system is ok. If it still does overheat then there is air in the system or the water pump is defective. The lack of a thermostat is not going to stop the coolant circulating if the water pump is ok and there is no air in the system. See my original post.
 

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Look, this isn't rocket surgery. Start with the least expensive fix and work your way up:

1. Air in the system
2. Thermostat
3. Radiator
4. Waterpump
5. Head gasket

Air in the system is pretty easy to eliminate so let's assume you've covered that. The radiator is new, so let's assume that isn't an issue either. A head gasket would be pretty appearent, as you would be loosing coolant and would see other signs of a failed gasket. That leaves the thermostat and waterpump. Water pumps usually work or they don't. It's highly unlikely that the waterpump is not providing 100% of it's required circulation without some very obvious noise, vibration, leak, or other manisfestation. So you are stuck with the thermostat. The fact that it's a non-OEM thermostat and not installed by you makes this a prime suspect, in my opinon. Before moving on to more expensive fixes, I would start with the least expensive/easiest fix first. Just my $.02.
 
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