I have a 1999 mercury cougar v6, my heat gauge will say it's overheating when I'm driving but when I pull up to a stop light it will go down . My gas gauge also fluctuates even when full but that problem is more annoying then concerning. Any ideas on what could be causing the temp gauge to fluctuate?

SOURCE: antifreeze ts boiling back into reservoir.

it sounds like a possible head gasket problem,you can get the fluctuation from combustion gases getting pumped into your cooling system and creating gas pockets,i would suggest taking it to a shop and have them do a block test to look for combustion in the cooling system to confirm the problem,that way you will know for sure,if it comes up negative they can also perform a flow test to make sure there is no restriction in the cooling system such as a plugged radiator or a bad thermostat,hope this sheds a little light on it

Testimonial: "I bet you've hit on the problem ! Car has been "using " antifreeze for a couple years now, with no leaking anywhere. Lost through the head gasket ?"

SOURCE: my 2002 monte carlo`s fuel gauge fluctuates from full to empty

Hi you need a fuel level sensor

SOURCE: gas gauge flucuates to empty and full so we never know if we have enough gas. What to do?

It is a common problem. It is a faulty in tank sender. You can just replace the sending unit by removing tank.

SOURCE: temperature gauge is fluctuating while driving.

I'm thinking the coolnat level is low, and this might be caused by a bad head gasket - At least $800 to fix - sorry.

SOURCE: Temperature gauge fluctuates

First of all you have a bad heater core that needs to be replaced. Second you may have a bad temperature sensor. Make sure the radiator if full of water