Temp gauge or Temp sensor problems

[hellaflushs14]

ok, so i hit a deer in my car about a month ago. well the car has been sitting for awhile now whilst the parts are being sourced and the body work is being done... btw no damage was done to the chassis, radiator, or engine. anyway, i have started it and let it warm up a few times a week just to keep it healthy and circulating fluids. well last night i start it, let it warm up, then give it a few revs to 4k rpm. everytime i would do that the temp needle would go from normal all the way back down to cold as soon as the rpms hit 2k.
what the hell could that be??? do i need a new gauge sending unit, a new temp sending unit, is it a short, or some faulty wiring. the only thing i have messed with since the wreck is the dash and the stereo head unit. i pulled it all out to hook up the ipod connection behind the unit. thats it.... please help...

[Marahutay]

dude i have the same problem every winter.
my car warms up normally and runs fine in 40+degrees weather, but as soon as it gets cold ill be lucky to get the temp needle half way to the normal operating temperature. Also, whenever it does reach the middle of the temp gauge, which is only when i let it sit and idle for almost 15 minutes, as soon as i rev the engine it goes right back down to cold.
However, it has never affected the way the car behaves when i drive it.
let me know what you do to fix this please. i havent had heat for the past 3 winters since i bought my 240.
thanks

[biggie]

Bad thermostat would be best bet.

[hellaflushs14]

yeah i have had a few mechanic friends say that i either didnt have any water or coolant in the radiator or my thermostat is sticking open...im guessin the thermostat...
im gunna put a superstat in and see what that changes, after that im goin with a new temp gauge...ill keep you posted though

[Marahutay]

but regardless of what the gauge says, wouldnt the coolant still be 'hot'? why would i not have any heat from my vents because of this if my coolant is still warm when i have great heat in my car as long as its not to cold outsid? would a thermo replacement fix my problem also?

[hellaflushs14]

no i the thermostat wouldnt help the heater problem but im guessin it will most likely fix both of our problems as far as the gauge and actual engine temp go, ur gunna be looking at prolly a new heater core, or something along those lines. givin im not a mechanic or anything...google the breakdown of a standard heater system and do some research, you could start by fixing small things that you think might be the problem and work your way forward trial and error style. definitely cheaper than taking it to a shop.

[LoserCard]

Your thermo is definitely stuck open if it 1) takes a long time to warm up, and 2) goes cold when you rev then engine. Your heater will not work properly when the thermo is open because your engine is flushing cool water through it instead of hot water. Don't get a new temp gauge yet, just change the thermostat. Most likely it will fix both problems.

[hellaflushs14]

well there it is, im gunna be putting a thermostat as soon as its ready to hit the road again, still prolly about a month away considering i need two new headlights and front aero, the headlights are ridiculous to find. the dealer wants six hundred but i can get a bro deal for 338 which still seems like alot....so anyway thanks for the replys definitely helps a whole lot

[allenms240]

Is it erratically jumping around?
If you're needle is erratically jumping around, it's a bad ground.
Next to the temperature coolant sensor, there is a black ground, clean it up and reconnect, should work better now.

[hellaflushs14]

no it justs sits at normal then when i rev past 2k rpm it just slams to cold and stays there

[breadbox]

does your upper rad hose look like its sucking closed? or do you know if it has a spring it in it?