Paccar MX13 Fuel Mileage, how can I get to 7mpg?

I now have the same truck and still averaging 6.7. that shows you the difference between the west coast and everywhere else east of the Rockies lol.

 

3.73 gears. It's always gonna suck fuel.

 

That gearing is your problem...I got a '20 T680 with the 510HP/1850TQ and my average is 7.8mph. 12 speed AMT and 2.79 rears. Usually set cruise at 67mph and pull a reefer....so 76K+ gross most of the time. I will say this...wind KILLS the MPG on these 680's
Slowing down is gonna give you the best results

 

How did you get 510 1850 torque with 12sp auto? I just bought a 579 with Paccar mx13 and 12sp auto and was told could not up-rate engine due to auto trans???

 

Dealer had this one sitting on the lot. The PO18F112C transmission is rated for 1850 tq.

So they said you had to have manual transmission for the 510hp?

 

Yup......I’ll have to check my trans model number.

 

EPA17 MX13 have 2 HP families. Low HP ones can only be taken to 455 HP.

 

Well that explains it, truck I bought is spec’d with PO16F112C12

 

Bummer

 

Meh.......I really don’t think I’d see a huge difference with the weights I pull.