My 95 pontiac grand am se has been saying low coolent even tho resivor is full radior don't have cap to fill there has been runing hotter then us to uselly runs at about 150 but now will jump up to 220 an stay there the needle on the temp gage jumps any ideas of what it coukd be

SOURCE: temperature/heat wont work/dashboard lights on and off

It sounds to me like you're low on coolant. When you checked the coolant level, did you actually open the radiator cap and make sure the radiator is full? The plastic tank you generally add coolant too is actually an 'overflow' or 'reserve' tank. There is a hose that runs from that tank to the top of the radiator so if the radiator gets low on coolant, more coolant -should- run in from the overflow tank. However in practice this does not always work. I have a Jeep that leaks coolant and experiences this exact same problem. Coolant will not run from the reserve tank into the radiator because the hose is plugged up, and whenever the radiator gets low on coolant the temp gauge will go real high and then drop, and the heater doesn't work well. This is because the cooling system of your car is supposed to be a closed system, full of coolant and no air. When coolant leaks out, the space it used to occupy is now occupied by air, which does not transfer heat well. When 'air' is passing through your cooling system, no heat can be transferred from your engine to the heater and radiator, resulting in a hot engine and no heat at the heater. Then when a pocket of water passes through the system, the temperature gauge quickly falls as the water absorbs the heat from the engine. The hot water that cools the engine is where the heater gets it's heat from as well, so when water passes through the heater core, the heater works, but when it's filled with air, it doesn't.

SOURCE: Intermittent overheating on 96 Jeep Grand Cherokee

I had this same problem on a taurus and did all the things you did and found out after that the coolant reserviour bottle had a crack in the bottom of it

SOURCE: 1999 Pontiac Grand Am Floating Gas Guage

 you have a bad connection or faulty tank gauge unit

Mike Deemer-White

• 96 Answers
• Posted on May 12, 2009

SOURCE: I have a 1990 Jeeep Grand Wagoneer that has a fuel an engine temp

Sending unit for the fuel gauge is not grounding correctly or is bad. Temp sensor needs to be replaced.

SOURCE: battery needle jumps normal to low (power draw) then all normal

Your voltage regulator is sticking a little.
I'm not sure but I think it is built into the alternator on these fords which means you may need to start thinking about a new one (either voltage regulator or alternator depending.)