temp gauge fluctuation

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baybaja
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temp gauge fluctuation

Post by baybaja »

Is it normal for my temp gauge (while driving) to go from the middle and slowly go towards cold and then go back to the middle? It usually starts to go to cold when I'm climbing a hill or am at high rpms
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anarchy1024
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Re: temp gauge fluctuation

Post by anarchy1024 »

baybaja wrote:Is it normal for my temp gauge (while driving) to go from the middle and slowly go towards cold and then go back to the middle? It usually starts to go to cold when I'm climbing a hill or am at high rpms
Mine fluctuates a little as the thermostat cycles, but it shouldn't be noticeable. The needle moves maybe 1-2 degrees after it reaches operating temperature, regardless of the road/load. How much is yours fluctuating by? Is the coolant in the reservoir above the MIN line?
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kamesama980
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Re: temp gauge fluctuation

Post by kamesama980 »

It might not be a problem (keep in mind most cars are dummy-fied (gauge is little more than an idiot light) to the point the temp gauge is rock steady in the center from about 140f-240f because people get worried about normal fluctuations). I'd get a more accurate gauge to check what temps you're actually running: I have a scangauge plugged in and have noticed my Baja is actually surprisingly linear with temp (as opposed to dummyfied) BUT from memory, still a 40-50f band where it doesn't move so if you're seeing it dip noticeably, it might be a problem.

That being said, at least it's dipping in the right direction. Generally, higher revs (at the same load) means more coolant is flowing for the same amount of heat being rejected by the engine (that the coolant carries away). So all other things being equal, higher coolant flow = cooler temperature. (the inverse is also true: loading up the engine at low revs will cause higher temperature: My last truck on flat highway at 80mph ran about 204f in 6th, 200 in 5th, 195 4th. 'course the mpgs tanked due to the higher rpm too).

All that aside, the thermostat ought to control the temps better. Do you have one? is it the right genuine Subaru one or a cheap aftermarket one?
-Russell
"You don't get to judge me for how I fix what you break"
03 sport 5mt
05 turbo 5mt vf39 and other STI bits, 3" turbo-back
baybaja
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Re: temp gauge fluctuation

Post by baybaja »

Honestly I have yet to go down and check the thermostat. But I just wanted to get some ideas. I've also read in a repair manual I've bought that the coolant temp sensor could be bad too, which could be a possible cause of why my car cranks longer on a hot start. But I will be looking into this soon.
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kamesama980
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Re: temp gauge fluctuation

Post by kamesama980 »

Could be. for reference, since I've been watching the temps and temp gauge, on my Baja it starts moving a little over 100f, the 1/3 tick mark is about 145f and it's rock steady center of the gauge from about 165f on up (haven't seen mine over 194).

A bad coolant temp sensor could do it, yes, though they fail completely more often than just shifting the scale.
-Russell
"You don't get to judge me for how I fix what you break"
03 sport 5mt
05 turbo 5mt vf39 and other STI bits, 3" turbo-back
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