fearce65

Start the car. Temp gauge stays cold. Cold air from the heater. Drive the car, temp gauge goes to hot, stomp on the gas in neutral a few times, heat comes on, temp goes to normal. Also, when running the air conditioner, runs hot or overheats. The fans are turning on. Any ideas.

brunobluto

Are you sure its completely full of coolant? Is your drive belt loose or broken? Sounds like its low of coolant or maybe the waterpump isnt working right. Might also check the thermostat.

fearce65

It's got coolant. Belt is fine. When I squeeze the hose, I can here the thermostat open and close.

MoneyShot

i would get it flushed regardless esp if the car has the original fluid. how long does it take to go from cold to norm or norm to hot or vice versa? and did this problem just now start or has it gradually got worst? if it is a new prob and the temp changes are quick, sound like that could be the thermostat is not working correctly and needs to be changed.

also where are you that you are using the A/C??????

Nuke

Is it a water antifreeze mix or straight water? The mix will run cooler than straight water.

brunobluto

I'm not sure that squeezing the hose thing means its working right. It opens and closes depending on temperature. It is easy and cheap to replace, so i would just do it and see if it helps. if nothing else you can eliminate it as a possible culprit. And as already suggested, i would get your entire cooling system flushed out, you may have a blockage resticting coolant flow.

MoneyShot

i was about to post that same thing. it opens at 195* not at a PSI so if it was the thermostat that was opening and closing then i think you found the problem.

fearce65

I don't believe it's a temperature thing. I was driving today. The temp guage stayed cold for about 5 minutes on the highway, cold air coming from the heater. Then the temp gauge went all the way to hot, still getting cold air. Coasted in nuetral and revved the engine. Finally got hot air and temp gauge went to normal. I'm beginning to believe that something is blocked and coolant is not circulating. The heater core was replaced two years ago and the water pump was replaced 5 years ago.

MoneyShot

kindly note that even though you may have a 4.6L i believe you have posted this in the wrong section. this is the S197 forums. there are forums for "modular mustangs" that would be more suited for you. This may be a problem that they have encountered before and could pin-point the problem.

Also note that these are still symptoms of a faulty thermostat and great candidate for a coolant flush. The thermostat may be opening way too late and letting the water get too hot before opening and letting water into the radiator. taking it to the side of the road and revving it like you have done is only going to make it hotter. while i do not personally recommend them, they do make thermostats that will open at 5-30 degrees cooler temperatures than OE one. At a $7 part this needs to be the first thing you try.

As far as the coolant flush goes, that will run you about $50 - $100 bux. make sure you take it to a reputable repair shop and ask them if they just replace the fluid or if they run clean water through the engine first. doing this will remove any debris from the coolant system and fresh coolant will carry heat better and make you car run cooler. you can do it yourself but the hard part is trying to find some place to take gallons and gallons of water/antifreeze.

Also you may want to check the fan replays. park the car and see if they turn on and off once the car is properly warmed up. finally once the problem is fixed let us know what it was so that we may better diagnose the problem with other MFers, Good luck