Temperature Problem? Whats going on here?

[Dweano]

Alright, awhile ago i was driving to school, temp gauge started as low as she goes like usual, then warms up to "normal" (about 1/3 of the gauge), then all of a sudden it warms right up to about half of the gauge and I'm like oh dang, contemplating pulling over...then all of a sudden bam, its down to a little bit below normal...and not slowly...it took about twenty seconds to go from "half the gauge" warm, to about "one quarter the gauge" warm. So it warmed up and cooled down randomly really fast. And it happened a few times, but about after ten mins everything was normal and it stayed normal. After school it happened a bit too. Whats going on here? And its not like I gunned it and kept it revved for a long time, i was cruising along at a constant speed and rpm. I also get pretty crappy mileage which may or may not be related.

[99RangerBoss]

sounds like a head gasket check out your oil and or your oil filler cap for white oily sludge kinda like a milk shake

[Dweano]

Awe damn, i was hoping it wouldn't be that. How major of a fix would a headgasket be?

[fordboi415]

Could also be a bad t-stat sounds like its sticking closed then openeing, would be worth the 10 bucks to repolace it

[SoLongStang9499]

It sounds like its just your thermostat opening and closing, usually it opens and closes very fast preventing from seeing any variation you've described. If it was cold outside it just may be your cooling system not staying up to temp due to the cold. To check this, when your temperature gauge starts to stay normal, turn on your heater on low but on full heat, If it falls again and then raises again, its completely normal. Your thermostat will ( and should only) open at i think 192 degrees I believe in stock form. So if your thermostat is opening, cooling the system to below 192 degrees, the thermostat will close. If its cold outside the cooling system would have more cooling capacity, and drop the temperature even lower when the thermostat opens, which would take some time for the system to heat up again to 192 degrees, which I think thats what your seeing.

[Dweano]

Phew, I'm hoping its just the thermostat, this would make sense actually because the older man i bought it from said he replaced the thermostat himself, so he could've got a cheap quality one, or installed it wrong or something. I'll look into replacing the thermostat.

[SoLongStang9499]

I really dont think you need to replace the thermostat either. If its heating up to norm temp, then cooling down below that, why would you expect your thermostat is malfunctioning? If anything, it seems your cooling system is functioning more effectiently then it needs to, thats just how i see it.

[Dweano]

It goes above what it normal was running at before, it used to run at a third of the gauge and when its jumping around it goes up to half the gauge or more. And its very erratic so something just doesn't seem right.