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Faulty Dash Temperature Gauge or Possibly Bad Water Pump - 2006 STI

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Xsplatz

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Discussion starter · #1 ·
I just noticed two weeks ago that my dash temp gauge needle was not at its normal spot while at a stop light(sitting just a hair below the wavy lines near the middle of the gauge). It was between the H and the tickmark below it. I have a Cobb AccessPort and always monitor the coolant temp, will explain why below, so when I looked at that, the temp was at 200 degrees. In the past 205 degrees would still keep the dash gauge rock steady the middle and the fans would kick on at 207 degrees. After moving again the dash gauge came back down to the normal range and the Cobb App was showing around 190 degrees. Anything close to 192 and up would cause the dash gauge to move now.

I have an 06 STI stage 2 Cobb w/mishimoto radiator and stock radiator caps. I rebuilt the engine with a new OEM short block at 215,000 miles. I had headlift/head gasket issues and I was pushing coolant into the overflow tank. I struggled with this for over a month testing and trying all sorts of things hoping it wasn't the heads. So I am familiar with all of the problems that go with head gasket issues as i had to burp my coolant system every day in order to drive the car. Because of this I have always monitored my engine temps. 205 was always the normal hot temp with the fans kicking in at 207.

Now at 3 years later at 230,500 I'm going through my checklist again.
  1. I'm not low on coolant.
  2. I'm not pushing any coolant into the overflow tank/ no bubble or material in the coolant.
  3. My radiator fans still kick on at 207 degrees.
  4. Cobb AccessPort has never shown the temps going above 207 even though the dash gauge displays like it is.
  5. I burped the coolant system 2 times.
  6. I replaced the thermostat and coolant with OEM.
After replacing the thermostat I burped the system and let the car sit overnight. The next day I did another burp but this time something usual happened. From all my previous times burping the car before the rebuild, I was always keeping an eye on the coolant level to add more as it was always going down with the bubbles. But this time the opposite happened.

I let the temps come up and around 191 degrees the dash gauge started to rise. I then realizes that the amount of coolant in the Lisle funnel was increasing a little around 195 degrees. Then at 200 degrees the funnel was now up to half filled. Worried it might over flow I plugged the funnel and I turned the AC on to help cool the radiator. At this point i could see the top radiator hose suck in a bit so i pulled the plug and the car sucked almost all of the coolant back in. So i could then repeat this process. As the engine temps go closer to 200 the funnel would fill, I could then turn the AC on and the fans would bring the temp down and the coolant level in the funnel.

Yes, Yes i know coolant expands when hot but i have burped the coolant system dozens of times up to 207 degrees where the fans kick in and never seen coolant push into the funnel like this. So here lies my confusion. Originally i thought it was a bad dash gauge since the Acessport never showed temp changes that matched the dash. But after seeing the coolant expand and fill the funnel could the water pump be the issue. Could it not be circulating the coolant and the path of least resistance for the expansion was up into the funnel.

Before I jump into a water pump replacement I'm just looking for any other thoughts on what could be causing this. Engine temps have been fine for 3 years and nothing has been done to the engine other then oil changes in this time.
 
#2 · (Edited)
Hmmm very interesting. I would think that if the water pump were faulty, you would be overheating which I believe you said you were very close to according to the gauge. Im guessing that when you did the rebuild, you replaced all timing components along with water pump right?

I think before you jump the gun here, lets try bleeding it again. Yes I know I know, you've done this a bunch of times but this does sound like you may have an air pocket trapped in there somewhere. At this point you have nothing to loose and everything to gain....

If you havent replaced both rad caps recently then do so now with brand new OEM ones.

Set your funnel assembly up on the upper smaller coolant tank. Put some coolant in the funnel. Set your heat to MAX temp and blower speed to low. Start the engine and begin the bleeding. Rev and hold the engine to like 2K and hold it for like 10 seconds. This will force the water pump to push coolant through. Then let idle for like 30 seconds. Repeat the reving and idling a couple of times. You should see some burping going on in the funnel as this is happening. It may not happen right away so thats why I say do it a couple of times. Feel free to squeeze the coolant hoses too while you're in the idle phases.

Once the fan kicks on, bleeding is now done and you should feel heat coming through the vents inside the car. Go drive the car for a while and put some miles on it. Check coolant level the next day and adjust if needed. Then if all is good, see if you coolant temp gauge is still acting up.

The reason im saying all of this is because I recently had a bad rad cap cause all kinds of problems for me. I believe the spring/valve in it was jamming and causing the car to suck in air by means of the overflow tank creating air pockets. One day the overflow tank would be almost empty, next day FULL. It was impossible to get the coolant level right. There were even times when I saw inconsistent coolant temp gauge fluctuations. Temp gauge would go down under heavy boost. I ended up replacing the rad caps, bleeding the system as mentioned, and all has been good since.
 
Discussion starter · #3 ·
Jay,

Thanks for the response.

Yes, i used all OEM timing belt and water pump components during the rebuild. I haven't seen many stories of Subaru water pumps going bad so I'm willing to test the other components first, that was why i swapped out the thermostat. I was hoping it was stuck/broken and causing the inconsistency.

I originally replaced both caps during the rebuild, but they are easy enough to replace so I will pick up another new set just to make sure. I did read a lot of other horror stories about bad radiator caps when searching the forum.

After i pick up the new caps i will bleed the system again and report back.
 
#4 ·
Jay11STI said:
The reason im saying all of this is because I recently had a bad rad cap cause all kinds of problems for me. I believe the spring/valve in it was jamming and causing the car to suck in air by means of the overflow tank creating air pockets. One day the overflow tank would be almost empty, next day FULL. It was impossible to get the coolant level right. There were even times when I saw inconsistent coolant temp gauge fluctuations. Temp gauge would go down under heavy boost. I ended up replacing the rad caps, bleeding the system as mentioned, and all has been good since.
Click to expand...
Aftermarket caps lead to overpressurizing my system and causing a coolant hose to snap and losing enough coolant for temps to hit 248. Always use OEM - lesson learned there.
 
#5 ·
could you have possibly installed the thermostat backwards? maybe this new one is defective? Could explain the coolant pushing into the funnel. As for your original problem, i believe but not 100% sure your STi has 2 coolant temp sensors one for ECU and one for the gauge, i would guess you need to replace the one for the gauge.
 
Discussion starter · #6 ·
Healtoer,

I'll start with the funnel. I used the smaller coolant reservoir near the turbo and st up the lisle funnel. I filled the funnel up with coolant, but only to the middle of the bottom V part (Maybe 2" of coolant, this was the second burping of the coolant system the next morning so i wasn't expecting to much change). After the engine hit 195 degrees i noticed the coolant level was rising in the funnel as the funnel level was now at the top of the V portion of the funnel. As the temps slowly climbed up to 200 degrees the coolant kept climbing. As i grabbed the plug to close the funnel off i could see the coolant flow steadily pushing into the funnel. At this point, with the plug in, coolant was maybe 2 inches from the top of the funnel. Im sure if i didn't plug the funnel it would have spilled over into the engine bay.

I then turned the AC on to get the rad fans spinning. As the engine temps went down towards 190 i was able to pull the plug and almost all of the coolant was sucked back into the engine. I could then watch and see if do the same thing again. Turn the AC off, let the engine temps rise to 195 and coolant was slowly climbing back up the neck of the funnel. With all of the burping/bleeding i did of the system before the rebuild i never saw this happen.

The original and new thermostat were both installed with the jiggle pin on top. And both thermostats ended up showing the same signs. I boil tested the old one and it open per manual specs.

Image


The 06 STI has the Version 5 (3pin sensor). There is only one sensor on the coolant crossover pipe. This was also replaced with OEM during the rebuild.

I was originally hoping there was a second sensor that i forgot.
 
Discussion starter · #7 ·
Jay,

I replaced both radiator caps. I burped the system again like you said with more rpm use during the burping. I still did not see any air bubbles.
After that system burp i took the car out. It is still showing the exact same behavior. Normal cruising is showing around 175 degrees on the Cobb app and the temp gauge is showing normal needle readings. If i pull over and let the car sit the temps will slowly increase and at 191 degrees on the cobb app the needle on the dash temp gauge will start to move up.

Now looking to see if anyone with a Cobb app can let me know if there temp gauge is still at the regular positions at 192 degrees.
 
#8 · (Edited)
Xsplatz said:
Jay,

I replaced both radiator caps. I burped the system again like you said with more rpm use during the burping. I still did not see any air bubbles.
After that system burp i took the car out. It is still showing the exact same behavior. Normal cruising is showing around 175 degrees on the Cobb app and the temp gauge is showing normal needle readings. If i pull over and let the car sit the temps will slowly increase and at 191 degrees on the cobb app the needle on the dash temp gauge will start to move up.

Now looking to see if anyone with a Cobb app can let me know if there temp gauge is still at the regular positions at 192 degrees.
Click to expand...
Interesting. Ok so it seems like the only time the temps go back down is when the car is out driving. Once it stops moving, and is stationary, the temp gauge moves towards hot. I think the water pump is going to run no matter what obv since its belt driven. In my experiences on other cars in the past, when mechanical water pumps fail, they usually leak or make noises. Sometimes both lol. I just dont see a new oem water pump/headgaskets going bad in 3 years and 15K.

Im not rulling anything out yet execpt the rad caps. However, like I said above, the car only starts to "overheat" once the car is stationary. Meaning no air passing through the front of the car towards the radiator. Even like you said, when you get the electric fans to kick on and operate the temps go down. Obv when the fans are in operation, there is air circulation. Tell me, do you have normal heat functionality? Does the heat feel normal in terms of temp output in accordance to your climate control settings? Also, is there even air flow (heat) out of all the interior vents?

How old is that mishimoto radiator? How many miles do you think are on that thing?
 
Discussion starter · #9 ·
Jay,

That was my thought about the water pump as well. I've checked in and around it and haven't seen any leaks or heard abnormal sounds.

The inside heat works fine. I can adjust throughout the range and can feel the air temps change accordingly. When burping the system ill crank the heat to max and the car will become an oven.

I installed the mishimoto radiator at 157,000 miles once the original started leaking. Haven't had any leaks or issues with it.
 
#10 ·
Xsplatz said:
Jay,

That was my thought about the water pump as well. I've checked in and around it and haven't seen any leaks or heard abnormal sounds.

The inside heat works fine. I can adjust throughout the range and can feel the air temps change accordingly. When burping the system ill crank the heat to max and the car will become an oven.

I installed the mishimoto radiator at 157,000 miles once the original started leaking. Haven't had any leaks or issues with it.
Click to expand...
Alright, so like 73K or so on the radiator. Dont really know the life span of a radiator but anything can happen. Ive never owned a mishi product but ive herd nothing but horror stories. I also dont like their quality. I honestly think they're popular because the name sounds cool. It sounds like a "jdm" brand and therefor it must be good, right? Lol, moving on...

Id say lets try an experiment to try and rule out the possibility of the radiator. Let the car start to "overheat" while stationary at idle. Get a leaf blower, big fan, shop fan, or something to that equivalant. Set it up to blow and push air through the front of the car as if you were driving. Try to focus it towards the front radiator. With the car trying to overheat and the leaf blower/fan assembly going and forcing air through, see if your temp gauge goes down back to normal.

Before doing the experiment, make sure there isn't any leaves, debris, or anything ridiculous obtructing the radiator.
 
Discussion starter · #11 ·
Jay,

That does sound about right. It definitely has a "Fast and Furious" sound to it. I think it was the only radiator i could get with next day shipping from RallySport back then.

So I went out and drove the car to warm the engine up. Below is what I consider normal operating coolant temps in the past this was from around 170ish all the way up to 205 degrees. (What i would see on the Copp App)
Image
 
Discussion starter · #12 ·
Now the below pics show the increase from 193, 196 and then 205 degrees from the Cobb Accessport. Right after 191 the needle starts to move up

193 196 205
Image
Image
Image
Image


As soon as the temp must have hit just above 205 degrees the radiator fans kicked on and brought the temps back down to 187. At this point the temp gauge was showing normal range again.

So the radiator fans are kicking on when the coolant temp sensor is hitting 205 degrees as seen in the access port. The question is should i be believing the Cobb Accessport value or the dash gauge needle??
 
#13 · (Edited)
Xsplatz said:
Now the below pics show the increase from 193, 196 and then 205 degrees from the Cobb Accessport. Right after 191 the needle starts to move up

193 196 205
View attachment 68486 View attachment 68487 View attachment 68488 View attachment 68489

As soon as the temp must have hit just above 205 degrees the radiator fans kicked on and brought the temps back down to 187. At this point the temp gauge was showing normal range again.

So the radiator fans are kicking on when the coolant temp sensor is hitting 205 degrees as seen in the access port. The question is should i be believing the Cobb Accessport value or the dash gauge needle??
Click to expand...
Just saw this, yeah that definitely isnt normal. My coolant temp gauge on my 2011 sti sit right around the middle and or just a hair over the middle. Depends on how you look at it. I dont really monitor coolant temps unless im going to really put the car through some punishment. With that being said, Ive hit coolant temps of 207-210 on the AP under heavy load situations. I have never seen the needle move more than its normal settings on my temp gauge.

I think you do have an issue here somewhere. Id be concerned with the gauge reading on the car. The fact that the fans kick on at the same time, everytime, at 205 degrees leads me to think that the actual coolant temp sensor and or fans are operating normally. Someone on here mentioned that there MAY be some other sensor specifically for the gauge but I dont remember ever hearing about that on the GD chassis cars. That may have been something for the GC cars. Maye look into that just to confirm.

I still think you should try my experiment recommendation. Im leaning more on the radiator being the issue. With my experiment recommendation, you can either condemn or eliminate the radiator.
 
Discussion starter · #14 ·
Jay,

I double checked and the GD only has the 1 coolant temp sensor located on the cross over pipe.

And i tried your experiment. I let the car heat up and used a leaf blower on the radiator. It lowered the temps as expected. I was also able to do the same with the AC. By turning it on the radiator fans kick on and can bring the temps down. So the radiator seems to be doing appropriate cooling that is needed.

I also hooked up my RomRaider laptop to check and make sure the Cobb AccessPort was reading the same. It matched the temps with the Cobb. Still showing the needle rising as soon as the coolant temp hits 191 and the fans kick on at 205. Still stumped on this one.

So it seems both software programs (Cobb and Romraider) are reading the temps in the correct range but the dash gauge is rising sooner. I'm guessing the dash gauge is using an voltage/resistance signal and maybe the wire or gauge is getting an incorrect or interfered signal. I'm going to try and see if i can see any issues with the wires coming out of the sensor.

Still not sure how the software can get a correct reading but the dash gauge cant.
 
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