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Bad gas mileage

I have a 07 Ford F150, 4.2 liter V-6, that the city gas mileage has fallen from 17 to 12.5, highway from 22 to 16.5, in that last year or so. Two garages have ran a test on the computer and can find nothing wrong. Anyone have any ideas?


Thermostat stuck open?

A thermostat that’s stuck open.

Bad coolant temp sensor to the computer.

Either of these will cause the computer to operate in the open loop mode. Which makes the computer think that the engine is always cold.


That truck was rated for 14 MPG city and 19 MPG highway. I my dad has a a similar truck ( a lighter 03 F-150 with the same V6) and he gets about 15-16 MPG overall. I have a hard time believing you’re getting 17 MPG city. But anyway, Could a thermostat that’s stuck open as the others have mentioned, or a sticking brake caliper. Or if you’ve replaced the tires recently with larger ones, that will throw off your odometer as well.

"Or if you've replaced the tires recently with larger ones, that will throw off your odometer as well."

Or, if the OP has recently bought tires with a higher rolling resistance…

I am constantly amazed at how many people fail to look at the rolling resistance ratings on tires before buying them. A friend of mine phoned me just before he finalized the purchase of new tires for his Rav-4. In addition to the fact that the “recommended” tires had really high rolling resistance, they also had poor scores in terms of both traction and heat resistance.

Luckily, I was able to convince him to NOT buy these old-technology Bridgestone tires from STS Tire, and instead to buy the far-superior Michelin Defenders from a different retailer.

Have you checked the tire pressure recently? Use the placard on the vehicle…not the tire pressure rating on the tire.