Sudden drop in fuel economy while towing

[Nebesa]

I have been pulling my 10,000lb rv for 4 years with my 2014 Ram 2500 6.4l, and fuel mileage has always been between 10 and 12 mpg.

This year, I pulled a 13,000lb dump trailer and the mileage was in the 5-6mpg range. I thought it was perhaps due to the trailer being heavier than I normally tow. Then I pulled my rv, and my mileage was again down in the 5-6mpg range.

The strange thing is, my mileage without the trailer is, and has been since I bought this truck, between 16-18mpg. I would think that if I was having issues with the fuel system, or the air filter, or the O2 sensor, that it would affect the mileage whether towing or not towing, but I'm only seeing the issue when towing. And it isn't showing any codes.

I've spoken to my mechanic who is a Chrysler/Ram/Jeep trained mechanic (his family used to own the local dealership), he first checked to see if there were any updates that needed to done, but everything is current. He is taking it on next week to try to diagnose, but at this point he's stumped.

Any thoughts from the community? Anyone else out there experience this kind of sudden change in fuel economy, but only while towing?

 

[Hagar1]

My 2012 used to get 22 -23 MPG but when I pulled a small trailer (16.5' Jayco) the fuel economy dropped it half.
I was lucky to get 12 with the trailer on. It was a little worrisome when travelling across Saskatchewan and Alberta what with the scarcity of gas stations.

 

[Nebesa]

I have been towing trailers for over 40 years, so I knew that my fuel economy was going to drop when towing. But the issue is that suddenly this season, that economy has dropped again. But as stated it has only dropped while towing.

 

[zrock]

could still be running winter fuel where you are filling up.. If its only when you were towing i would say its a trailer issue and not a truck issue.

 

[Nebesa]

It has happened with two different trailers, if it had been just with my rv, then I would suspect dragging brakes, or a wheel bearing or axle problem. But with two different trailers, I am more suspicious of it being a truck problem.

 

[crash68]

How many miles on the truck?
Might be worth doing a compression check on all cylinders. Another thought would be to check the valve-train operation.

 

[Dean2]

How many times, and how far, have you towed your RV with the lower mileage. Are you using Tow haul and did you before. Is it possible you had a head wind you don't normally have. Have you disconnected the battery over night and let the PU go through a re-learn cycle?

If your pickup gets the same mileage empty it always did then the only variable is more drag when towing than you used to have, which means something about the resistance when towing has changed.

 

[20IndyRam]

Problems tend to show up when you're working the vehicle hard. Temps increase (water, oil, trans) and in general the drive system is stressed. Ignition, fuel, compression, cooling - It could be any number of issues that is only showing up when the system is loaded (your 6.4 is loafing without a load). Taking the vehicle in is a good idea.

You may also want to investigate your brake controller. Can't say that I've seen seen one fail "partially on", but I suppose it's a possibility.

 

[SolidWaste]

Could there be a weird connection in the Hitch Connector or wiring that is slightly applying the trailer brakes?
Other than that, If the Obvious stuff was checked that is weird.

 

[dieselscout80]

I would check/ consider / replace all the easy stuff fit.

However, wonder if your transmission could be slipping under a heavier load?

Have you noticed higher transmission temperature readings?