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Cavalier Starting in the 1980s. the Cavalier made a name for itself by offering an affordable 2 and 4 door compact.
Platform: J-body

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Old 02-01-2011, 05:42 PM
CF Beginner
Join Date: Dec 2010
Posts: 7
Default 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)
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Old 02-01-2011, 06:29 PM
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Join Date: Mar 2010
Location: Saint Amant, Acadiana
Posts: 171

Colder the engine richer the mixture, MPG is directly affected by engine temperature.
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Old 05-30-2013, 12:22 AM
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Join Date: May 2013
Posts: 1
Default 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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