engine heating and cooling

[quote:0cdd90e042="fattyford77"]My 1992 F-150 302 v8 4x4 auto trans is having a problem keeping the thermostat were it should be. I just put a new one in and when I start driving it goes up to the normal line then goes straight back to the cold. If I leave it idle it will raise up to n or o. When I'm driving it will come down just above the normal line and when i brake or slow down it goes below to the c. The old thermostat and the new do the same thing. What am I doing wrong. Thanks[/quote:0cdd90e042]

do you have heat or the heat temp change with the movement of the gauge
because it may be you are dealing with temp sending switch sending wrong signal to the dash
check the connector on it (clean and lube)
check / flush radiator and coolant system
good luck