Cooling system

So I have fluctuation in temp range. When fully warmed up the car sits at 194 degrees F. Then after 5 mins time laps by then the highest I see the temp go to is 208 degrees F. But it will not get any hotter. Also I sat in the car for 20 mins watching the temp on the Cobb AP. The fans kicked on and off many times, and it would cook itself down to 194-192 every time, it's just weird because it will go from 192-208 just from idling for 20 mins, it would do it rapidly, and not overheat. Because the normal operating temp for our cars is 200 degrees F...so the gauge cluster I'm reading is way above the second line, but on the Cobb AP is only 208 which should be on the second line exactly, correct me if I am wrong.

So the guesses I have what the culprit could be is:

Coolant temp sensor
Air (I have burped the system many times with my 50$ funnel.) lol
So I kno it's not air, maybe the cap on the reservoir?
Or the cap on the mishimoto radiator? Or both caps? Because the system has been burped and I check every morning and the reservoir is literally 1 tbsp of water that is low...

I have no leaks, and no coolant in my oil.
I have no oil in my coolant. No bad head gasket.

Please tell me what you think it could be. I feel the temp range is normal for a built motor, but my cluster giving me a hotter reading than what the Cobb AP is giving me is whats concerning me. So bad coolant temp sensor?


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Also I might add oil temp does not go above 110 degrees C after driving "boost heavy" if you will, for over an hour one way to my cabin which is over 50+ miles away.. Oil temp is good cruising, stays at 96-100 degrees C, it stays at 90, if on highway speeds cruising


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It all sounds pretty normal to me. The cluster is less reliable than the accessport reading. The accessport sees what the ECU sees so my guess would be a bad gauge sensor. I forget where my gauge sits. I never refer to it.

I don't kno how to explain better but the range from 192-208 the needle on the cluster moves way more than it should, I might replace the coolant temp sensor one day and post results, also a faulty coolant temp gauge refers back to the ECU's AFR as well, as it adjusts for the correct fuel based on coolant temp and flow. The faulty sensor can cause bad AFR's and rough idle, and boost issues.


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Thanks for the input [MENTION=9]HolyCrapItsFast[/MENTION]


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STIMULA8 said:

I don't kno how to explain better but the range from 192-208 the needle on the cluster moves way more than it should, I might replace the coolant temp sensor one day and post results, also a faulty coolant temp gauge refers back to the ECU's AFR as well, as it adjusts for the correct fuel based on coolant temp and flow. The faulty sensor can cause bad AFR's and rough idle, and boost issues.


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Click to expand...

If the AccessPort is reporting the correct temperatures, then that is the temperature the ECU is reading and your AFR's should be normal. At that point, my only conclusion is the gauge itself is bad. In looking at the wire diagram for your car, it uses the same grounds that you had an issue with when you removed your manifold. Perhaps that issue somehow caused damage to the gauge. :tup: That circuit is pretty simple and straight forward.

Here is some more info... On the STi the thermostat and the coolant temp sensor are in the same sensor so if one is bad you have to replace both by default, The good news is that they are isolated internally. So the same sensor can report different readings to the gauge and the ECU and the two remain isolated. That said, the gauge reading should have no influence with the ECU. If your AFR's are influenced and the AccessPort is reporting normal temps, then you may be looking at something unrelated in that regard.

Thanks so much for the diagram, it will really help me out a lot looking for this behind the cluster. You da man


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