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gas mileage help with two avalanches but same size engine

Ski4343

New Member
Joined
Oct 11, 2020
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5
I own a 2005 1500 with 5.3 flex fuel engine and the readout says I am averaging about 16 mpg. I just bought an 2003 with 5.3 non flex fuel and it is averaging about 13. Same gear ratios 373. The 05 has 183K on it and 03 has 96k, Any thoughts on the difference
 
Pull a spark plug from each and compare.Id imagine you've replaced them in one by now while the other might be running factory plugs. GM changed the recommended plug type and gap around 2008 or so with a tsb.

I always recommend running a few tanks of fuel treatment like amsoil PI or techron once a year and right after buying a vehicle.

Those two combined things jumped my 2001 tahoe about that amount. The plugs were basically completely worn down at 117k.

Depending on how new the 2003 is to you, it might just need some usage and standard maintenence to clean up it's act. Stupid things like the previous owner not changing their oil enough can have an affect.


Beyond that, simple stuff like air filter, tire pressure, tire tread type, and your driving habbits in each will all have an affect.

I'd also recomend tracking your mileage with something like fuelly.com instead of using the computer when comparing it to another vehicle. That computer number is most accurate only to itself.
 
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same fuel?
 
I would not trust the onboard computers for gas mileage figures they have been found to not be very accurate. Best way is old math with fill tank and record mileage for several tankfuls. There can be various reasons for differances in addition to what was already mentioned above, air temp, wind, driving conditions such as stop and go as well as time idling, then tire size and tread as well as tire pressure...on and on.....
 
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