P0128 Coolant Thermostat

[sr139fox]

I put a new thermostat housing and thermostat on this summer. Everything is running great, no leaks, coolant loss, or any problems. I noticed with the extra cold days this winter that the engine temperature does not run at normal. As a matter of fact, if I run the heater, it almost makes it to the cold line on the gauge. This depends on how cold it is in North Carolina. Another thing I noticed is it appears to have better gas millage. Have not checked it, but my millage between tanks is more. In the summer, I prefer a cooler running thermostat when it is almost 100 Degrees in the shade. I think the thermostat is stuck open or just bypassing too much. Is this something I should look into soon, or let it ride until the next thermostat housing starts leaking? This is the third housing installed, factory, and 2 replacements. When the weather clears, I will put my code reader and check the temperatures after a long ride. Vehicle has about 153,000 miles.
Dave P.

 

[mustang6878]

I would double check that you plugged the sensor on the thermostat housing back in and that it is tight. Then I would look at the temp sending unit.

Are you getting good heat?

 

[sr139fox]

Yes, I get good heat, but it is cooler. I usally have to turn the temp knob mid range, but now its on full. When I run the heater, the tem gauge will drop to a cooler indication.