Luke warm heat...2003 taurus

I have an 03 Taurus,u code 3.0...has had luke warm heat going on its second year...had super hot heat up till then.Car has 120,000 miles..was power and backed flushed and filled at 80,000...heat worked great before and after...right amount and mix of antifreeze...no rusty gunk in overflow ,coolent looks and tests to -40...gauge is where it should be...just never warm and never gets hot.....open thermostat??....worse? thanks for any help.

Does the engine temp gauge get to the high side of normal after a few minutes of driving, or does the gauge stay low as well?

-Rod

The car takes a little longer to warm up....extra 5 min or so...then go's to right in the middle of the gauge......I have owned this car since brand new.....temp gauge is right where it has always been for 11 yrs.It does not go to the high side of normal....the only thing that has changed is the hotness of the heat...this is the same now for going on the second winter...so...was great for the first 9 of the 11 yrs.Thanks for the reply.

Since the gauge seems to be working as expected (I see I missed that comment in your original post) I doubt you have an open thermostat. It would seem that either your flow through the heater core may be restricted or you may have a stuck blend door for the Heat/Ventilation/AC (HVAC) system.

Do you have an IR thermometer that you could use to measure the inlet and outlet temperatures of the hoses for the heater core, and compare those with the inlet temperature of the radiator?

Are the HVAC controls manual (knobs) or electronic? If electronic there is a self diagnostic mode that may indicate if there is an issue with the blend door. History suggests that it's a bit hit or miss though when it comes to identifying blend door failures.

-Rod

I don't have anything to test the temp on the hoses...might be the blend door...doesn't get as cold as it did...I just thought it was age and maybe needed a shot of coolant....the controls are manual ...I think I know how to check the motor that opens and closes the blend door....2 screws and a small metal panel....right....the control for the door is behind this....is that correct? Take the screws off,take the panel out f the way and see if it is working all the way...both ways...or at all....correct?