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Just a quick question if you guys wouldn't mind humoring me.

R/T Tuning bled and filled the car up with Glycol coolant about a week ago. After a couple of 2+ hour drives I wouldn't imagine all the air bubbles are out. I also know we don't have the most accurate system, but when is the needle considered to be "high" on the temp gauge. The needle today (~45*F) seemed to be a tad higher than normal, but no where near the middle of the gauge by any means. Just a tad higher than it normally sits right above the first tick. Now, if it is reading slightly higher during 45* weather, I am a bit nervous for when it becomes 85* weather. Also I my drive I did notice the temp needle drop a bit from it's normal position then rise back up. Could this have been from the fans turning on when I was in traffic and then started driving? I know this isn't a huge deal and may seem like nothing, but I want the car running healthy for the summer. Thanks for any help guys. I may take a drive again later today (car was sitting for 4 days) and try to get a pic of what I think might be the needle being a tad high on the gauge.
 

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High is the second mark on the gauge and up. Anywhere in between those two marks is normal operating temperature. Anywhere below the first mark is considered cold.
 

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Discussion Starter #3
High is the second mark on the gauge and up. Anywhere in between those two marks is normal operating temperature. Anywhere below the first mark is considered cold.
Did not know that. So even if you're right below the second tick as opposed to right above the first tick, that's still considered normal operating temp? Or is that excessively high?

Any issues with Glycol coolant?
 

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Not very educated on Subaru coolant temps other than to say if our needle moves from what has been typical in the last 140,000 miles...I would be concerned. Always just a tick above the first line.

The Cobb AP does have an option to watch actual temps...certainly far more accurate than the analog gauge. Mine touched 210 once, if I recall correctly.

Hope that helps.
 

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The stock gauge sucks.

If you have an AP I would keep track of it that way. Anything from 180 - 215 I would consider normal.

Like B said though, unless your getting above that second line I wouldn't worry about it. If your getting large temp fluctuations you need to re bleed your system.
 

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Sounds like you had air in the system after the coolant change. How is it now? The upper end of the stock gauge is approx 230 deg actual coolant temp...once it gets to the top of the gauge its closer to 240 deg. It can get that hot during the bleeding process but should quickly cool down as coolant is added to replace the air.

At the point you are describing on the gauge you are probably seeing 207 degrees and then the fans come on and drop it back down, but it shouldnt go below the first mark on the guage once its has reached operating temp. Even at 187 degrees my stock gauge stays a tick above the first mark on the gauge.

Your temps will spike with air in the system, but as long as your not driving it for miles like that, it wont hurt anything; the coolant shouldnt get hot enough to boil or boil out of the overflow...it it gets THAT hot then its probably exceeding 250 degrees and that is hot enough to damage the engine if your driving at speed. Pull over and let it cool if it gets to the top of the gauge and get it somewhere to bleed the cooling system.

I thought I read on here that the Subaru ECU has a failsafe and will shut the engine off at a certain overheat temp?? But I wouldnt worry if you dont hear the coolant boiling or if it only got hot for a short period of time and you werent on the highway or driving for miles like that. But it's best to pull over and let it cool to insure that you dont get to a temp that can boil the coolant
 

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i had low coolant after doing work on the turbo and reading from my AP the temp climbed up to 230 at red lights but when i went over 45 it cooled down to the normal 198. filled it up and bleed the system and its always at 198. so you shouldnt worry about being to hot for a short amount of time. the other guys on here also have some good info
 

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Yooooo bringing this tread back, I recently replaced my radiator at the 105k service to an aluminum rad from Mishimoto. Is it normal for my temp gauge to fluctuate lower at times? This happens usually when I'm either goin downhill on a highway, or I sometimes have good throttle modulation on a flat surface on the highway 6th gear @ 80mph. It does not get higher than the normal op-temp, but at times it dips just below the first notch mark. Also will this lowered temp cause my car to run rich til it's back up? Thanks all.
 

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Define "fluctuate", do you mean a constant "up down up down" motion on the same down hill stretch or it'll move up to normal op temp while driving under load and when going down hill the temp needle (or gauge reading) drops but returns to "normal" when resuming putting the engine under load again? As for running rich, watch your AFRs. Rich is better than lean, but unless I'm missing something the coolant temp shouldn't have an affect on fuel trims, AFRs, etc.
 

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Define "fluctuate", do you mean a constant "up down up down" motion on the same down hill stretch or it'll move up to normal op temp while driving under load and when going down hill the temp needle (or gauge reading) drops but returns to "normal" when resuming putting the engine under load again? As for running rich, watch your AFRs. Rich is better than lean, but unless I'm missing something the coolant temp shouldn't have an affect on fuel trims, AFRs, etc.
Hey, thanks for reply... Ehh I think "fluctuate" might have been the wrong word... Idk maybe. Yea when I'm not under load, it seems to drop(the temp needle) a tad bit, even on flat surface. And yes it comes back up after several seconds of mild load. Obviously 70-80 mph highway it does stay steady above the first notch line, but goes down when I'm cruising on a down hill. My old Civic or my wife's Toyota RAV4 never showed any temp "fluctuation" in accordance to drive load...

I really don't beat on the car since I'm usually carrying my daughter in the back. I've read in other threads about "racing" thermostats opening early and keeping the temp lower than "operating temp". It was stated that people will suffer from running rich because the ECU is detecting the less than normal operating temps. But I had the regular Subaru thermostat installed 2k miles ago with my service. I don't have an AF gauge or an accessport to determine any of those factors. Our cars run rich naturally anyway right? Anyway thanks again. I'm still slowly learning the basics to STIs :cool:
 

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Might be a bad thermostat, especially if it didn't do it before replacement...also could be an air bubble, but leaning toward bad t-stat.

Try this: Unplug the thermostat heater and see if the temperature still drops under those conditions. You will get a code for open circuit to the t-stat heater (so I think) but you can clear it later or it will eventually clear itself after you plug it back in. If it cures the problem it means the ECM is forcing the t-stat to open even though it isn't necessary. That indicates a sensor problem. If it still drops in temperature that pretty much confirms a defective thermostat.
 

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Might be a bad thermostat, especially if it didn't do it before replacement...also could be an air bubble, but leaning toward bad t-stat.

Try this: Unplug the thermostat heater and see if the temperature still drops under those conditions. You will get a code for open circuit to the t-stat heater (so I think) but you can clear it later or it will eventually clear itself after you plug it back in. If it cures the problem it means the ECM is forcing the t-stat to open even though it isn't necessary. That indicates a sensor problem. If it still drops in temperature that pretty much confirms a defective thermostat.
The thermostat is not electronically controlled. It opens purely based temperature. Either it works properly, or it doesn't and needs to be replaced.

I replaced my tstat with a new OEM one when I put in my Mishimoto radiator and I've never had issues with the temperature changing like that... It sounds like either the new Tstat wasn't installed properly, or its faulty... Either way, I'd start there.
 

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unless I'm missing something the coolant temp shouldn't have an affect on fuel trims, AFRs, etc.
whut.
it definitely should affect AFRs, maybe not by enough to be important though if its only fluctuating say 10 or 20 degrees.

If that was true, cars wouldn't richen up on cold starts.
 

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Howdy guys, bumping the thread...AGAIN. I didn't get a clear answer to my previous question and my car is still lowering temps on the dash gauge. Thermostat is fine, installed correctly. I have no air pockets running through my system, engine and rad are full of water. So finally it's August and San Diego, Ca is seeing 100deg ambient temps, I'm moderately using the AC for my wife and kid in the car. I drive quite spiritedly but I still notice my temp gauge lowering as I have decreased load on the engine. Can I assume this is normal for my car? Is the Mishimoto actually a very well engineered heat dissipating system? I'm running 50/50 Subaru coolant in my car. I do not have an accessport so I wouldn't be able to really tell the water temp. But yes even on a hot day where temps reach 105 outside, it still seems to lower with decreased load. Downshifting to slow down, exiting the highway, downhill coasting... Just lowers itself and then it comes back up once I load up the engine and start spooling moderately. I'd say it dips below the first notch quite a bit, to the point where I see the squiggly lines of the temp gauge logo. Once again, it's a Mishimoto rad, Subaru blue 50/50, OEM thermostat in excellent condition and is installed properly, system is bled out no air pockets.
 

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I'd bet air in the system...or low coolant.

Best way I've bled the Subaru system is with one of those funnels while the engine runs.

The needle on the factory gauge should move negligible...unless really caning it!

Something is wrong.
 

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I'd bet air in the system...or low coolant.

Best way I've bled the Subaru system is with one of those funnels while the engine runs.

The needle on the factory gauge should move negligible...unless really caning it!

Something is wrong.

I'm 100% sure the cooling system has no air and is completely burped. When I did my timing belt service I put the new rad and bled the system at least 8x. Did the "morning after" top off too. My rad is full of coolant and so is the coolant res tank. Yes I also used that big coolant funnel that has the radiator cap base so I was pretty much on point. The car isn't overheating at all. It just estranges me that the temp gauge reads lower than normal operating temp with less load on the engine. Literally I don't have a heavy foot lol. Should I assume my thermostat is over-compensating? Bah I need to get an A/P asap to really tell. I don't want my ECU to think my car is cold and it starts running richer than a pro athelete's bank account, screwing with my A/F and possibly making more carbon deposits overtime. Could it be low voltage? However I do not notice my lights dimming or anything electrically wrong with the car. Its just so weird I don't find turbo-hot STi's to run "that cool". Decreased load = lower. Increased load = returns to normal.
 

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Factory Subaru coolant gauge (like most cars) has a huge temperature swing with the needle moving nil.

If you are seeing the needle move...that is not right when up to temp. Take it to a dealer...only few things that are culprit.
 

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Hey folks, quick thread bump...

SoCal started having "cold" weather over the last few days. I'm seeing 45F ambient mornings on my way to work. Monitoring via AP3, is 192-194F coolant temp normal for cruising at 80mph? I usually saw between 187-190F few weeks back when the weather was still "summer like".
-Stock T-stat
-Mishimoto rad
-OEM Subaru blue coolant 50/50
-IA Performance tuned in August

Thanks in advance.
 

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bumping this thread again, anyone has found a solution to this problem?

Car is a 2005 STI (all stock)
the original radiator cracked and caused the car to overheat to the 3rd line on the dashboard (towed it back home).
I replaced it with the OEM KOYO radiator, all the coolant hoses (from Subaru), thermostat with gasket (from subaru) and Subaru Green coolant with conditioner.

I have replaced the thermostat twice with oem and burped the system multiple times.

the temp gauge drops to the first mark as shown in the picture below, it doesn't have a specific time, but mainly when i go like 80 mph on the freeway or cruising downhill.

 
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