My 2003 cooper s, heater stopped getting hot. Then the temp gauge pegged out. replaced the the thermostat, Now if I stop at a long red light, the temp rises very quickly. What is wrong?

SOURCE: 2001 mitsubishi eclipe heater does

It could be very well your water pump from the sounds of it. When was the last time you had that check or replaced? That would be my next guess to the problem...what's your mileage on the car?

SOURCE: Intermitant temperature

Check to make sure your thermostat works right by monitoring the warming up of your engine. With a completely cold engine, start and run the engine for a few minutes, then put your hand on the top radiator hose to monitor if and when it gets warm as the thermostat opens more and more and note the gauge reading( if it works) the top radiator hose should be unbearably hot within 5-8 minutes. If the therm. opens right it should close right aswell, staying open a little while eventhough the radiator may have cooled may be what you are experiencing causing the rapid cooling and is nothing to worry about. The Hose should not get warm very soon after starting the engine. Regarding you gauge, lets take one step at a time, verify proper op. or the therm.

SOURCE: water temp mal function

Unfortunately No, All of the Guages run straight into the Computer. If you bypass them you will have error codes out the Wazzu and lights on the Dash Constantly. Try a Salvage yard for a Replacement Guage Cluster.

SOURCE: just replaced radiator, but temp. gauge is rising to the red line

preform a pressurized collant flush , take it to a raidior shop to have it done , they will clean and blow out all blockages that might cause your car to over heat. also check to make sure you dont have air pockets in your anit freeze, if you do you need to bleed the system out after you have it flushed , your car should have a blead valve to let out the axcess air ,if not drive it down the road with the cooaint overflow cap off , not the radiator but you need to flush out the system first , add new anti freeze then bleed out all air pockets, hope this helps

SOURCE: The temp gauge on my 2003 chevy impala is pegged hot when idling, but goes down as I drive. Is this a thermostat problem?

The most probable cause is air in the system. If all fans kick on then it can only be air in the system or problem would accure when driving too. A pocket of air will cause a small vortex and it take far more pressure to get anything around it. Like fluid. To burp the system....when your car is cooled off, remove the radiator cap and then start it up....it will push all the air out the top and you will see bubbles and maybe even some fluid shoot out. Just make sure you add back to correct levels when all done. This running process has taken me as long as 30 mins to get all the way out. Its easy and free but DO keep an eye on the temp guage while the cars just idealing to get the air out.