95 legacy engine temp. gauge puzzle

yeah I know....the old (defective) one will probably open at correct temp is what I meant. Not sure what that temp is though.....if that's what you meant?

Dont want to extend this thread longer than necessary 777, but how could the stat be responsible for the overheating trouble described by dtate if it opens at the right temp? Feeling like I missed something somewhere... 8o

Ok.....I'll try and explain the best I can.

I'm assuming you know what a standard thermostat looks like correct? They are maybe 1.5-2" deep/total height. They are not very big at all. The OEM Subaru thermostat is probably 3-4" deep/total height. Plus as someone mentioned it is not perfectly centered. It is offset a little, and has a little thing that probably lets air through.

Now here is my explanation to what is happening. The smaller thermostat does not go up into the engine block as far as the subaru one does. The cooling system on the legacies is VERY good. I'm not sure which way the coolant flows, (top to bottom or bottom to top) But for arguments sake, let's say it flows top to bottom. You have cooler coolant flowing out of the radiator back into the engine. This cooler coolant may just be enough to close the thermostat, partially or all together. Also the OEM thermostat could be less sensitive to a change in temperature, therefore fluctuations in temperature over a short period of time will not affect it, as could an aftermarket. Also flow rates of the coolant could affect the thermostat in the same way, whether it opens more or less....and how that affects it I'm not sure.

I do know for sure, that if you replace the stock thermostat with one that is not OEM, you WILL have problems....whether it be overheating or sporadic temp gauge, or something else. I have experienced this first hand with mine. I replaced my thermostat several years ago, and the car would warm up, and if you revved the engine, the temp gauge would just sink. This was even after the car had been warmed up and running for a while.

Without actually seeing how much each thermostat opens, it's reaction to a change in temp, flow rates, depth in the engine block, and any other variables you can throw in there I can not give you a 100% factual reason why. This is speculation or a theory on my part to why the thermostat/engine is exhibiting the characteristics it is.

Hope that helps explain my reasoning.

Questions, comments....?

Josh, your theory seems to reflect what may have been going on with my car. While checking out the system before replacing the thermostat, I would feel the radiator hoses, the top one would be hot, the lower one cold. This seems to indicate that the coolant flows from the bottom to top. As you stated, the OEM thermostat is much longer than the one that was in the car. I did test the stat I removed, and it would open, but I didn't check the water temp. when I did the test. Anyway, two days with the new stat and no problems with the gauge!!

« I'm assuming you know what a standard thermostat looks like correct?
They are maybe1.5-2" deep/total height. They are not very big at all. The OEM Subaru thermostat is
probably 3-4" deep/total height. Plus as someone mentioned it is not perfectly centered. It is offset a little, and has a little thing that probably lets air through.»

[Yes to the first question : I replaced a few and have one right on my desk waiting for the next occasion to go into the Brighton. It's genuine Subaru ordnance and bears the part number 21200AA072. It is exactly 2 1/4 inches in height, 2 1/8 inches across, is excentric like you say and has this small wiggly little peg in a hole near the circumference just like you say. This part looks solid, has a beefy spring, stainless steel armature and solid brass core. Just beside it, I have an after market one, same diameter, but only 1 1/2 inch in height. It looks...well...cheapo, very much cheapo. The minute I saw the real thing, the after market one became paper weight !]

« Now here is my explanation to what is happening. The smaller thermostat does not go up
into the engine block as far as the subaru one does. The cooling system on the legacies
is VERY good. I'm not sure which way the coolant flows, (top to bottom or bottom to top) »

[It flows top to bottom]

« But for arguments sake, let's say it flows top to bottom. You have cooler coolant flowing
out of the radiator back into the engine. This cooler coolant may just be enough to close the thermostat, partially or all together. Also the OEM thermostat could be less sensitive to a change in temperature, therefore fluctuations in temperature over a short period of time will not affect it, as could an aftermarket. Also flow rates of the coolant could affect the thermostat in the same way, whether it opens more or less....and how that affects it I'm not sure. »

« I do know for sure, that if you replace the stock thermostat with one that is not OEM, you
WILL have problems....whether it be overheating or sporadic temp gauge, or something
else. I have experienced this first hand with mine. I replaced my thermostat several years
ago, and the car would warm up, and if you revved the engine, the temp gauge would just sink. This was even after the car had been warmed up and running for a while. »

« Without actually seeing how much each thermostat opens, it's reaction to a change in
temp, flow rates, depth in the engine block, and any other variables you can throw in there
I can not give you a 100% factual reason why. This is speculation or a theory on my part
to why the thermostat/engine is exhibiting the characteristics it is.

Hope that helps explain my reasoning.

Questions, comments....? »

[I think you're right on the whole. I just made a test comparison with both stats hung side by side on a wire in a pot of hot water. First, the flow opening of the OEM stat is 1 1/2 inch and the opening of the after market one is 1 inch only. The Subaru stat is a 78°C (172°F) and the other one is 82° C (179°F). At 180° F, the Subaru stat is fully open (wide open) and the other one is only starting to open. It wont be open fully (and that's not much compared to the real thing) until 190°F.
The part where your theory specially seems to check true is in the closing phase of both. The after market one is fully closed when the temp drops back to 175°F (much faster reaction like you predicted). The OEM one is still half open at 170°F (reacts slower).
The after market stat could obviously cause problems in a less than new cooling system.]

Nice call Josh!!

Glenn O

Very very cool Gilles!

Thanks for actually running the tests and confirming what I theorized

This is one of those cases where the scientific method or what not worked out.....we gathered data and stuff, made a theory on why it was happening, then tested the theory and draw conclusions on whether it did what we expected or not.

Maybe we could go into business and test subaru stuff.....ya think they'd pay us to drive around a subie and test stuff


Russ, this is probably worth archiving when it starts to fall to the bottom of the page.

Glad the team work worked, 777.
I not only want to be ready to make any maintenance and repair on my car, but I love to understand how things work in a car even if mine does not have thst particular problem at the time. This board is my university in that respect and i read almost all that is posted. I try to do my homework right and be able to help on some occasions.
Mery Christmas to you and to all other members.

Thanks Gilles,

and Merry Christmas to everyone

Ok Josh I'll archive it in a few days, presuming we get no more posts on it. Good thread!

Josh & Giles, thanks spending the time and energy explaining what was going on with the two thermostats. I'm glad to see that this string will be archived. Merry Christmas to all!!
David

Welcome

Merry Christmas

I need archiving....I was on the 2nd page....I don't want to fall off the board....help help....please I'm drowning.....hehehe

And for those of you questioning.....I'm only partially psycho...you only wish I was a fully psycho....mwahahaha

PS: Russ if you don't want my psychotic episode in the archive, you can delete it...