Hi guys I tried searching but couldn't find anything with my exact problem. I first noticed an issue with my heat not blowing warm this past winter when I was stopped for a few minutes idling then once I start going it would blow warm again. The same thing has been happening in the summer with the AC then just today my temperature starting getting very close to the H so I quick turned my heat on and it started going down. My antifreeze is filled to the top at both the cap and reservoir. I'm seeing a lot of info about bleeding the coolant system or changing the fluid... What should I do first? Btw i have a 04 coupe 6mt with about 63k miles. Thanks!

 

sounds like the blend door actuator.
Not 100% sure but that definitely sounds like the problem.
you can get one for 20-40 bucks.

 

Also check your heater hoses that go into the heater core. Get the car warmed up and feel to Make sure they are both hot. If one is hot and one is cold the heater core is plugged

 

Would the blend door cause the temp to rise though?

 

Oh I gotcha, thought u meant the air vent temp not the engine temp.
So it's overheating,
Thermostat maybe?
Make sure your fans are kicking in, they can fail.
Also I've heard air sometimes gets into the cooling system, there's a bleeder screw on passenger side on a heater hose. Lots of threads here on how to bleed it properly.
Also the radiator cap is known to cause overheating problems.