Is my engine heat sensor on my 94 f150 5.0 is bad or going bad, is it suppose to trip the check engine light. It has not triped, yet my temp gauge is still fluctuating. Would the coolant mix have anything to do with it. And what are the manufacturers specification on how my coolant to fill with after draining. Thanks for all your help. Just trying to avoid tacking it to the shop.

 

It won't throw up the CEL if it is bad/ going bad, the mix doesn't have anything to do with it, usually. Close the drain plug, put your heat control to maximum heat(in the cab) start adding coolant to the reservoir until it's full, then leave the radiator cap off to make sure there isn't any air in the system and turn your truck on until coolant runs through the radiator, turn the engine off, let cool, then add some more coolant to until you get to the lip of the radiator filler neck. Squeeze the upper radiator hose to get rid of any air that might be in there, then add some more coolant if you need to, then you're good to go.

 

have you checked the wire from the temp sender for a short? if the fluctuations are erratic, that could be a cause.

temp senders are pretty cheap too, you could just replace it and see if it works out... I'm really not familiar with how they act when they go out.. whether the fluctuate or just die.

 

The computer doesn't use the gauge sensor, it has its own.