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Sudden low MPG

6K views 8 replies 6 participants last post by  HeavyAssault 
#1 ·
Sorry, this is a little long but I need help. Driving a 2016 F350 and last month we towed our travel trailer to a local park. Got 8MPG to and from. After I put the trailer up, my MPG was at 13 on the freeway. It had been at 17-18 before. I thought made it would get better as I drove and I was still on the same tank of diesel. Later, as I filled it, I noticed the "miles to empty" notice on the display showed over 80 miles less than it normally did. Put in a diesel additive and continued to drive. No change so I took it to my local dealer. Computer showed nothing. A week later my CEL came on and this time it was the DEF heater and assembly (responded to a earlier post about that). Changed that but mileage still in the tank. I don't think it's a blocked fuel filter because it's running like a champ, just the MPGs suck. Dealer said it was the winter blend diesel but I've been using the same source (no biofuel). Location: East Texas. Vehicle is stock and has 60,000 miles on it. Can't do any deletes, still under extended warranty. Any suggestions?
 
#2 ·
Winter diesel does give lower mileage. Also the miles to empty is constantly being updated where it updated the value displayed that quickly or not.
 
#3 ·
What are night time temps in East TX?

Winter blend diesel does give lower MPG as pointed out above but warm parts of the country don’t see much blending.

How many tanks have you gone through now? Might take 2-3 to see a real trend.

It helps that you use the same station each time.

Tire pressure the same?
Air filter clean?

Do you use fuel supplement?
 
#4 ·
Deleting the emissions system from your truck won't help fuel millage at all just so you know. I use the trip meter to gauge exactly what my fuel millage is. It will tell you time, how many gallons used and MPG's. That is the more accurate way to get your fuel millage. That instant MPG's thingy isn't the most reliable source.
The reason your DTE was so low the computer says a 26 gallon tank with 13 MPG's and this is the distance you can travel. if the gauge said 17 the number would be different. Thats the reason for the difference. When I;m towing I use the 100 miles to empty and start looking for fuel other than that i pay no attention to that gauge.
 
#5 ·
I've been thru at least 4 tanks of diesel. It seems to fluctuate from tank to tank. Most tanks read low MPG, one tank read 16, I thought the problem was solved. Mileage is of the trip meter, not odometer. Next couple of tanks I'll check using good old math. As for temps, what can I say, it's Texas. A couple of days is was 60 during the day and 30's at night. It now 30's during the day and 20's at night. Diesel comes from same source, even same source as last winter but didn't have this kind of drop in MPG.
 
#7 ·
When I replaced the tires on my truck I lost some millage. I didn't go bigger just stock size. I have a combined MPG of 15. Towing I average 11 to 12 and that is combined towing and just driving around. I have made two 3 month trips aand that was the millage I got. Both trips coast to coast
 
#8 ·
Common to have drop in MPG with new tires if the old ones had worn out tread.
 
#9 ·
2015 F350 SRW...128k+ miles....16+ City.....18+HWY@70+mph sustained over 7 hours of driving....modded. More power, more reliability, more fun, more driving, NO worries.
 
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