About 2 weeks ago, I got a yellow engine light (manual mentions not having full engine power).
I took my CM in, turns out the thermostat was bad. It took a day to get the part in and a half day to fix. So I was without my CM for 2 days .

Since I've had it back, my average MPG indicator has been at 24.4 and has not moved at all. Before I took it in, I was getting 25.5 to 25.6. It would fluctuate between the two and has never gone below 25.5.

Has anyone with heard anything about this?

 

Had the thermostat done twice now, but no negative impact on gas mileage or the indicator.

 

Try zeroing it out along with your average speed. At least that way, you can tell if it is working.

 

This car should have a temp gauge.
Did it fail open or closed ?
Did you overheat?

As for MPG indicator, I assume you already reset the average speed and MPG history...right.

 

Did you accidentally push the SPORT button while using a cup holder? Otherwise, I cannot see that the two issues could be related.