Mpg question (optimual rpm)

Everyone’s MPGs lower during winter. It’s normal. Two main reasons why it happens are cold weather creating more air resistance and tire PSI lowering.

Aside from winter, wind speed will drop your MPGs to the floor. In fact, wind speed is more serious than cold weather. I can see my MPG on my gauge lower as soon as I hit wind speeds over 15 mph.

 

Less BTU's in winter fuel as well. Takes more fuel to make the same power.

 

Those RPMs are kind of low. It’s true that lower RPMs will give you higher MPGs, but if the terrain has a bunch of hills, you’ll end up downshifting many times, lowering your MPGs.

Unfortunately your truck is spec’d to run 1100-1150 at 62 mph. I believe that can be changed if they plug in the computer. My truck gives me 1300 rpm at 62 mph. I can get higher MPGs if I lower my rpm, but then I’ll be driving at 55, which I don’t do.

 

I think you’re misunderstanding 1100-1150. The picture you posted shows an rpm of 1400-1500.

By the way, that green light on the dash is probably the recommended rpm. I drove a 2016 Kenworth T680, and I remember it having the light as well.

 

The picture is also showing 73 or so, the OP said he’s 1100 at 62.

 

I used to sell lots of fuel filters on windy days in Nm, some people just didn't want to believe how much wind robbed them of power.
It is sometimes better to drop a gear to maintain speed in the wind, instead of trying to push a head or even a cross wind at low rpm.

 

If you have a boost gauge start paying attention to it and don't be afraid to drop a gear and run a couple miles an hour slower.

The lower the boost, the less load on the engine.
Sometime dropping a gear will give you better economy in certain conditions.

It doesn't happen often, but sometimes the wind hits the truck at such an angle from the side with enough velocity to break the tractors slipstream, get between truck and trailer.
I've found through experimentation that in a case like that you can improve your economy by driving a few MPH faster.
If the truck is moving faster the wind doesn't have enough time or force to overcome the slip of the truck.

Next time you're bucking a wind and pulling steady on the flats keep an eye on your gauges and play with it between 55-65 MPH, see what you can do.

Back in 2001 I left home with one of 4 loads all destined for the same customer, a little over 800 miles, windy all the way, I ran on my own and the other 3 trucks ran together.
I left a little early and moseyed, they left later and drove a bit harder.
When we fuelled I pumped 100 litres, (26 gallons), less than the best of the three.
In the end they probably gained an hour or so on me, but it cost them to do it.

 

Which engine do you have?
Could be helpful.

 

When I fueled last, which would be the second time since winter diesel, my mileage dropped a full 1 mpg. That's huge.

 

The only unfortunately I see is he is running snails pace. If he is getting 11-1150 from at 62. Then if he was driving 72mph his rpm would be 1350-1400