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Discussion Starter · #1 · (Edited)
Anybody ever notice their gauge move around?

The other day it was 48C outside and I was in freeway traffic. Usually the gauge stays at ~1/3 (at the lower level of the "thermometer" symbol on its face) but I noticed that from lower speeds and with high throttle (accelerating) the gauge moved to ~2/3 (the top of the thermometer). It then dropped again and then fluctuated between those two areas.

The car has never done this before.

I suspect environmental/ambient temps were ridiculously high because at one point the AC cut out (implying extreme head pressures and and overwhelmed condenser; when airflow resumed not only did the coolant temp needle drop but the AC resumed producing cold air).

I've not seen this before and I've not been able to replicate the behavior. I pressure tested the cooling system -- it holds pressure great with the motor off. I see no bubbling in the overflow reservoir. I see and smell no coolant.

EDIT: More info: I was unable to replicate the fluctuation in the temp needle at 40C ambient temps during the day and I certainly was unable to replicate the issue at 28C tonight. I'm not about to drive to Death Valley in 2nd gear for further testing.

I'm switching to a 2-core Al radiator thinking my 1-core Koyo got overwhelmed.

Anyone thinking "head gaskets" on this one though? Note that the car never overheated in that the needle never reached red. TIA.
 

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Have you checked the fans operation?
 

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Discussion Starter · #3 ·
Good point, thanks! With the AC on, both fans come on. I have no "fan logic fault" CEL either. As far as I can work out the fans (probably) work. Granted the fans are dual speed and I've no way of knowing if they engage at full speed or not -- merely that they do engage.

I also can't find any debris on the condenser or the radiator itself.

Tomorrow it'll be 40C again (sigh...) and I'll try to drive on the freeway with the AC on in 3rd gear like a jackass. Hopefully I won't be able to replicate any issue again; that'll indicate to me that the issue happens above 47C (a condition I've encountered precisely once in 16 years of ownership).
 

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I’m not sure what trips the fans activation however I still wouldn’t rule it out as you said the temperature issue arises while stationary and goes away with movement. I don’t know of a way to test the fan speed without a rpm gun and some reflective tape. You may still have two speeds, but the wrong two.

Another issue could be a failing water pump. Less likely but not a reach.

Honestly I’d lean towards an air movement issue over a pump issue.

I don’t think I’ve ever seen a build thread for your car so I’ll assume it’s straight out of the fast and furious. Do you see any other issues if you monitor anything like afr or egt?
 

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Discussion Starter · #5 ·
The issue arose under moderate speed and very high ambient temps with the engine under load. Temps fall at high speed or idle.

Subaru built my car... It’s stock!

The fan logic is documented and I remember... remembering it but I’ve since forgotten what I once remembered other than the fact I did once remember it. I’ll search my own posts (sigh...). I even posted the temps involved once upon a time. I bet it’s in my manual!

I’ll see what happens in mid day her today and see when I can fit a bigger rad and go from there.

Thanks!
 

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just make sure that 2 core isn't mishimoto, they are prone to leaks.

I haven't heard of many having issues with the koyo Rad; and that's with track use.

Do you have an oil temperature gauge? It is possible that your oil temperature was causing the coolant temperature to rise since the stock oil cooler is really an "oil warmer" and more of a fallacy then anything?

I just wouldn't jump right away into replacing the koyo.


XJ also brings up a good point, if your fan thermostat switch is stock, then the koyo is doing the best it can to keep cool without the assistance of air through the fins. However, when the temp finally gets high enough, the fans kick in and cool it back down.
 

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Discussion Starter · #7 ·
The Koyo is their single core plastic tank OEM clone unit not their race unit. I avoided Mishimoto and gambled on an Amazon cheapie 2-core; if it’s rubbish I’ll get a Koyo 2-core instead.

Thanks guys!
 

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I would also guess 118.4F :))) has something to do with it.
I once took a head off my Buick only to find white gunk in the coolant passages; one seemed almost completely plugged. In normal ambient temps such a thing may not matter but in such temps as you describe, it just may be the difference between system overwhelm and not.

Also, I had a Dodge van whose radiator would almost constantly gunk up and cause just what you describe (heat up under load and at idle {not enough 'flow'} but then go back down under moderate speeds.) I had to rod it a couple times then replace it.

good luck
 

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I genuinely am not convinced radiator. It’s not difficult to switch out but buying a new one only to have an underlying issue that comes back will suck. There are a lot of people who live in places where 110°freedom units are common and still maintain constant coolant temp.

In my limited knowledge fluctuations arise most often when there are air flow issues over the radiator or fluid movement issues usually from a thermostat. If it cools off quick at idle you know fluid is moving and you have adequate airflow in that situation. If it’s cooling well at high speed you can suspect the same.

Pressure test on the system checks. Coolant fill checks. No contamination. That leads me to believe thermostat, air bubble, or fans. Do you have a way to jack the front of the car way up before bleeding?

I know you’ve got miles on the car, and I vaguely remember a thread about the timing belt, or perhaps hoses, that you’ve done in the last year or two. When you did the timing belt job did you use a Subaru thermostat and pump? I’ve heard hit and miss feelings about the gates pumps.
 

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Discussion Starter · #10 ·
I initially used a Gates pump but 60K later it leaked and I went to an Aisin. It’s been there 50K now.

Thermostat is Subaru dealer part. I have circulation.

OK I’m forming a plan: drive the car hoping it’s hot today (so far we’ve had TWO earthquakes this morning so for all I know the sky will fall). If it doesn’t overheat I can’t fix it but I’ll change the rad and coolant for fun. If it overheats I’ll swap the rad and the thermostat and save up money for head gaskets just in case.

I’m good at burping and my fans spin up. I’m left with

Nothing wrong except 47C and high load
Obstructed rad
Thermostat
Head gaskets

And I’m suspecting I have them in order decreasing likelihood too.

I’m in no mood for HGs today!
 

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Discussion Starter · #11 ·
Correction: three earthquakes.
 

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Discussion Starter · #12 ·
Regarding the fans, and quoting myself from another thread (I now don't remember where I got the info but I probably knew what the hell I was talking about back then) here's the story:

On the 2002 car turbo car, if the temp is below 95C, the fan is off.

If the temp is between 95C and 99C and the speed is below 43 kph, the fan is on.

If the temp stays in that region but the speed increases beyond 43 kph, the fan is off.

If the temp exceeds 100C the fan is on regardless of vehicle speed.

If the A/C is turned on (this includes the defroster regardless of A/C switch position) then the fans switch to A/C mode instead.

This tells me that I saw elevated coolant temps when the ambient temps at the nearest weather station were 47C, airflow was moderate due to speed over 43kph but load was high (accelerating in 2nd, 3rd for example) and the AC was on. I'm left with really hot air going into a hot engine bay etc. Didn't mention, but the bonnet hurt my finger to touch -- the nose of the car must have been really hot -- and this also explains the AC cutting out (I'm betting the compressor has a high pressure failsafe off switch just like domestic units).
 

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Discussion Starter · #15 ·
Ha!

I’ll be honest: I’ve never understood nonmetric units! I’ve never needed to do so...

OK so I was about to post about my inability to replicate the issue. I drove 60km in 25C weather and zero fluctuation. Maybe this afternoon we’ll warm up again.
 

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Well keep this updated so we know an answer for the future.
 

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Discussion Starter · #17 ·
I certainly will, thank you!
 

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I want you to know I keep really odd hours, and you either also keep very odd hours or you have a bigger issue with insomnia than I do.
 

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Discussion Starter · #19 ·
I stay awake some nights. Other nights I’m too tired — I carry the world’s winters...
 

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How were the temperatures in the dash around the cluster? Could this be a gauge malfunction? Any chance you run a data logger to confirm the reading?

The only time I've seen my gauge cluster move is when the radiator fan cut a slit in the upper radiator hose and I lost coolant. The gauge would sit normal when I was moving, but would climb when I slowed. Coolant smells are unnerving. It's good that you already checked for this condition.
 
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