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Old 01-01-2012, 11:02 AM   #1
02bugeyedimp
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Default Thermostat question

02 Outback Sport 2.5 MT

Is it normal for the thermostat to only open when I get above 3000 RPM's? if I cruise around and keep the revs low, or I shift before I hit 3k the temp goes all the way to 215-220 and the lower radiator hose stays cold (not just cooler then the upper hose or rad) as soon as I raise the revs up the thermo opens and the temp drops.
1 is this the normal operation for subies?
2 is that temp too high for the engine?

full story... bought the car with 160k was told the timing belt was changed @5000 mi ago, but not the water pump or pulleys, temp gauge went up and down but only went up about 2/5's of the way, thot this was juz the way it was as it was cold and there were no other signs of it overheating.
Came out of a shop one day to see some coolant dripping out of the car, hooked up my scan tool to monitor the engine temp and it was overheating. Narrowed it down to it being the thermostat since the lower rad hose wasn't getting hot no matter how hot the engine was. I replaced the thermo with one from AZ but it still did the same thing (open only when over 3k) I took it out and tested it and it worked fine, even tested the original one (which was also from AZ as the previous owner replaced it when he did his timing belt)
By the time I noticed all this the HG had already started leaking (oil in coolant) so I replaced the gasket, head bolts, water pump, thermostat (with a fail safe one) and a couple other things only to have it still do the same thing. It's not overheating as long as I keep the RPM's up but it seems to get hot when I idle low, or shift low.
I tried searching the forums, web, and asking techs I know (including the dealership). Any thots????
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Old 01-02-2012, 12:30 AM   #2
littlewhitewagon
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Where did you get the water pump from? Are you sure you got all the air out of the system?
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Old 01-02-2012, 12:14 PM   #3
02bugeyedimp
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Water pump is from auto zone, and I'm pretty sure I got all the air out. Ran it with the heat on and rad cap off till it was @ 200 and the coolant was flowing (not bubbling) ot the top of the rad, then let it sit with the cap off till cool, topped it off and did it again. then closed it up drove it. Let it cool with the cap off overnight and repeated the next day.
Another thing when I ran the car with out the thermo it worked fine, well it ran cold the whole time, but never got hot.
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Old 01-04-2012, 09:59 PM   #4
02bugeyedimp
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Bump anyone???? Any thot's? Is that the normal way a thermo works on a subie? Any thot's of what it cud be?
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Old 01-05-2012, 09:04 AM   #5
rkramer
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My bet would be that you have air in the system. Subaru's are notoriously tricky to get burped correctly.
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Old 01-06-2012, 10:39 AM   #6
littlewhitewagon
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Or the water pump is no good.
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Old 01-06-2012, 09:35 PM   #7
02bugeyedimp
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So it shudn't take the RPM's getting up so high to open the thermostat?
Can't see how there cud still be air in the system, I know how hard subies can be to burp; anyone have a better idea then the way I did it above?
Wud using an aftermarket thermostat make a diff? Stock is 172.5 and the one I used is 175.
I know on every other cooling system I've worked on there is no correlation between the RPM's and the thermo working, unless it's a performance engine that has an electric thermostat sensor if some kind.
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Old 01-07-2012, 10:51 PM   #8
littlewhitewagon
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The thermostat opens based on temp not pressure. You want to see if your thermostat is good? Take it out and put it in a pot of water and start the fire. When the water gets to the rated temp, it should open. As you turn off the fire, and the water cools, it will close.
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Old 01-07-2012, 11:43 PM   #9
02bugeyedimp
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I know that thermostats work off temp not pressure, which is why I find this situation so bizar, I've tested every thermostat I put it and took out.
Does anyone know if the ej25 in the bugeye has a valve between the water pump and heater core?
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Old 01-09-2012, 08:48 PM   #10
02bugeyedimp
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Bump!!! Anyone know if there is a valve in the by pass going to the heater core?
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Old 01-10-2012, 11:30 AM   #11
JamesWilson2
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Clogged up radiator? My '00 Legacy (EJ25) had that happen, though different circumstances than yours....HG were fine, system bled and burped, new t-stat, etc but would still overheat. Radiator was cruddy after 215K+ miles.
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Old 01-12-2012, 09:24 PM   #12
02bugeyedimp
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When the thermo is removed it flows fine and regulates the temp perfectly.
Does anyone know if there is a valve on the line going to the heater core, or anywhere else in the cooling system that wud need the extra RPM's to push the coolant past?
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Old 01-13-2012, 12:07 AM   #13
SAx Colin STi
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First thing that comes to mind is the bozo autozone water pump can't flow enough or a few impellers already broke.
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Old 03-25-2012, 03:26 PM   #14
quikrex
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To bring this back to life I just had this same issue it's a bust thermostat stuck closed! The reason the temp drops at higher rpm is coz the water pump is working harder. At idle and low rpm or even going down a hill at 40mph in neutral the car overheats moment you chuck it into gear and rev her the temp drops down... New thermostat and all fixed!
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