2020 ST temperature gage & fast idle issues

[Boss 351]

I have an issues with my 2020 ST in which the temperature gage stays low , and moves up when warming up . Then, gage will go back down to just above 'C' and engine will take a long time to come of the fats idle circuit. T-stat was replaced with no avail. Has anyone had this issue ? Looks like engine can be running for 20-30 min., and fast idle circuit stays on half the time . Been to dealer 3 times ; I tell them maybe it's the temp. sensor or ? Can anyone help? thanks
Dave Christo

 

[SimonsGTS]

What was the brand of the replacement thermostat? A lot of aftermarkets can be defective, if so try an OE stat from the dealer, they're usually much better quality. At the same time you can verify it's seated properly and not allowing coolant to bypass the stat.

 

[Boss 351]

Was covered under warranty with FordTech & parts . Did not fix the issues. I think it is the temp. sensor on the engine , and wondered if any others had this sane issue?

 

[TXCarbonized]

It should start giving you code P0128 if the coolant temp never gets high enough. Most likely either the thermostat or temperature sensor.

 

[MikeHTally]

Sure sounds like a sticking thermostat. I've had one like that. Usually they just fail, but I had one that would intermittently stick. I've heard of brand-new ones bad out-of-the-box. Maybe you should get one of those laser temp sensor gadgets. They're not expensive.