I saw there was another strange temperature issue recently posted but i think my situation was different enough to do a new post

I have a 2003 evo, basic bolt-ons. I had been having a problem with not having heat and as New England has been getting colder it was becoming a bigger problem. I replaced the gears, cable and blend door with no luck. Bled the coolant of air bubbles with no change. Than i decided to change the thermostat "just in case". The car was warming up normally but i had noticed the electric fan never would turn on.

So i replaced the thermostat & rebled the coolant system. The problem im having now is that the car takes a VERY long time to warm up, and will only do so if its sitting. The car will reach normal temps after sitting for about 10mins, but as soon as the car starts moving the temperature drops back down to "C" within a few mins even at just 15-20mph.

The weird thing is that the electric fan does kick on now and when the car gets up to temp i DO have heat now. It just gets colder as i drive the car and the temperature drops again. The only difference i had noticed was the old t-stat was 80degrees and the new one is 82degrees

Any ideas or help would be appreciated.
-Matt

 

The new thermostat could be sticking open. Are you able to hook up a scan tool to the obd 2 port and look at the actual temp value at what your coolant temps are at? You could also have a bad coolant temp sensor. When those things go out they default at -40 degrees.