New to this forum and looking for info on why my 2016 Chevy Silverado with a 5.3L engine and 183K miles has significant mpg drop (City 19mpg has dropped to 13 mpg). I’ve had it to shop and they say there are no codes showing. I have recently changed spark plugs and wires, cleaned throttle body and injectors. I have checked my mpg using truck digital screens and also completed mpg calls manually. Both numbers match. I’ve recently had alignment checked and that was ok. Shop claims that bad MAF or Oxygen sensors would throw codes but no codes are showing. Looking at other things to check. I’m going to change my thermostat this week. Current operating temps running between 178 and 181 degrees.

 

You might consider a compression check. Are you using any oil?

 

I am not burning oil or losing any. I changed my fill synthetic oil every 6000 miles. I haven’t done a compression check so can add that to my system checks. Thank you

 

I have 2016 Silverado with 5.3L as well. I just recently changed my thermostat - my temps were running slightly lower than yours. The OEM setpoint is 207F (97C). So, it seems yours needs changing just like mine did. That should help with your fuel economy but I don't think it will give you back the entire 6 mpg you've lost.

I used this AC Delco Gold thermostat - it works great. Coolant temp is 207F now.
https://www.rockauto.com/en/moreinfo...t=2200&jsn=526

When you're checking temperature use a scan tool - not the coolant temperature gauge on the dash.

 

Thanks. I have purchased a thermostat and should get it tomorrow. Then I’m going to install later in the week. We’ll see if it helps.