P0128 code - Thermostat - Chevrolet Forum - Chevy Enthusiasts Forums

P0128 code - Thermostat

Join Date: Dec 2010
Posts: 7

February 1st, 2011, 4:42 PM   #1  
CF Beginner
P0128 code - Thermostat

This code came up for my car.

P0128-Thermostat opening too soon causing engine to run cold. (now fixed)

Would this be a possible cause for somewhat low mpg?

Just don't feel my Cavalier is getting the best mileage.

Average at 27mpg (mostly highway)

Join Date: Mar 2010
Posts: 171
Saint Amant, Acadiana

February 1st, 2011, 5:29 PM   #2  
CF Active Member
Colder the engine richer the mixture, MPG is directly affected by engine temperature.

Join Date: May 2013
Posts: 1

May 29th, 2013, 11:22 PM   #3  
CF Beginner
Too Cold

If the engine runs too cold then the computer will always be in ' warm up ' mode and say that it needs more gas. The idle may be up as well.

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