Drop in MPGs
 

I have an 06 Ram with a Quadzilla Xzillerader chip and a drop in AFE air filter with holes drilled in the factory box. Otherwise, the truck has no mods. I recently moved from SC to MD and have noticed a sharp drop in my fuel economy since October. At that time I replaced the original Michelin A/S(I ran these around 65psi) tires with BFG A/T's(I run these around 60-65psi) but kept the same size(265/70/17). I drive mostly highway miles and was getting 18.5-21 hand calculated for about 4 months. In October after getting the new tires I dropped to 15-17 mpg. Is this typical for a more aggressive tread but same sized tire switch? I'm told that states further north than my previous home in SC mix Number 1 and 2 diesel fuels and this will decrease mileage. Is this an expected level to drop considering the different tires as well? I have had a fuel filter change and ran some Stanadyne and got even worse fuel economy with the additive(barely 15). The water pump also went out since this started and the truck was in a Dodge garage and no other problems were noted. I have also cleaned the air filter. Am I missing anything else or should I get used to this? Its getting tougher to justify the truck having sold the boat it was intended to tow and getting worse fuel economy. Sorry for the 20 questions and thanks for any help you may be able to offer.

The winter blend of fuel will cause a drop in mpgs. I lost 1 mpg and my Ford buddy lost a little over 1 mpg as well. It will come back up in the spring......

The tire change alone counts for the drop. Given stock tire dimensions/specs, the more "open" the tread, the worse the fuel mileage. The MICHELIN LTX A/S is a "green" low rolling resistance tire, that companies best for mpg and long life.

Fuel can also make a difference, especially in colder climates. Frankly, warm weather (above 50F) means more, IMO.

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When I installed my BFG's (315-70-17's) going from the factoy BFG Rugged Trails I didn't see any fuel mileage change. I usually see a 1-2mpg decrease on winter fuel, more the 1mpg than the 2.

Normally I would sat to change the fuel filter and change/clean you air filter, but you said you did this, SO, all that remains IS the tire change. I really find it hard to believe that you would have had that great of an amount in mileage change due to tires alone.

Try adding some cetane to your fuel and see if that brings it back up.


CD

Thanks for the tips and reassurance. Guess I'll stick it out through winter and see if it comes back up in the spring. Yet one more reason I'm looking forward to moving back to the southeast.

You southern boys, sheeze!!!
In places that actually experience WINTER, it's normal to see fuel mileage drop. Even in my car I see about 50 less km per tank during the cold months. Right now, I'm getting about 50 less miles per tank from my truck, 23 vs. 25 mpg.
Never quite understood this. Colder air is more dense thus it should be more efficient, right? I'm guessing there is also more friction throughout the drivetrain, colder gear oil etc.

There is more to winter mileage than the fuel. There is a less than 3% difference in BTU's between #1 and #2, and if its a blend that number is even smaller. I also believe many stations now chemically winterize their fuel, so the BTU content wont change.

The biggest difference in winter is the additional hp required to get the truck moving with cold fluids, cold tires, and more dense air, and the added time to get the motor to operating temp where it will operate efficiently. My truck makes almost 2x as much boost to drive 80 in 10* weather as it does in 80* weather.

I think its just easier to blame the fuel than to blame all the reasons.

The new tires will also make a decent difference. The stock ones are very low resistance, and that resistance decreases as the tires wear, near bald tires get the best mileage and new tires get the worst.

Diesels (mine, at least) are more efficient with more heat in them.

Last winter I was driving across WY on I-80. Up until Laramie it's pretty flat. In 75 mile sections I had an open grill, winter cover with all flaps open, and winter cover with all flaps closed. I don't have any way to moniter intake temp. But with all flaps closed the water temp hovered around 195*. That's where it got the best mileage.

https://www.dieseltruckresource.com/...y-t267100.html

On a 10* day with all 4 flaps open the IAT's are around 100 at 80 mph, I dont want to know what they are with all 4 closed.

Between cold winter temps, winter fuel and my Copper STT I use as my winter snow tires on the truck, I lose 4-4.5 mpg compared to spring to fall time of the year.

I'd like to know. Maybe a higher intake temp makes the engine more efficient? Maybe it doesn't.

I am going on a 300 mile drive tomorrow. I will leave the cover on, all 4 open and see how it does. Temps will start in the single digits and end up in the low teens.

Just commented on the same thing in another thread talking about the LSD to ULSD change. I can always tell when they change the blends becuase my fuel milage will do just as stated, drops 1 mpg in the winter/fall and picks it back up again in the spring according to the overhead meter.

My truck makes almost 2x as much boost to drive 80 in 10* weather as it does in 80* weather.

Wow!

Warm-up is key. I've seen discussions elsewhere about coolant, oil, trans, axle heaters to try to reduce time/miles of warm-up. If op temp is, say, 180F then starting from 80F or 20F isn't as big a difference as it seems, it still takes 100 to 160F heat rise.

And even here in near-Mexico it takes 30-miles or more to fully warm-up a cold CTD. Tires change pressure around until 1.5-hrs at steady state speed, minimum (the point where they stop changing).

"Coolant warm-up" means little. Important, but tip-of-the-iceberg.

^ same here ! on days like today when it is about 8* it takes my truck about 15-16 lbs of boost to do 70 mph. In the summer it is usually 5-7 psi to do 70 mph