Squeezing The Gallon

I've got a ScanGauge on my dash. It connects to the OBD-II port on my van and can display all the computer readings. I don't know what a lot of them are, but I do like the MPG readout and also the one that shows trans fluid temp...especially since I'm towing a boat/trailer that's 11,000#.

So I see I'm getting about 6mpg at 55mph. That's not good seeing as I have 2000 miles to go. And what's worse is that even on slight hills she downshifts to maintain speed and then gets about 3mpg. So I put her on 52 mph and see a good 1+ MPG improvement, but the hills are still killing me.

I set one of the fields on my GPS to Vertical Speed. It tells me when I'm going uphill and can let up on the gas to keep her from downshifting. I now have figured out that when I'm running 1,600rpm (at 8mpg) that when she downshifts to 2,100, the MPG's drop to 5+. I don't have a lot of luck with the Vertical Speed indicator to prevent shifting. Further experimenting shows anything under 2,000 rpm is best.

I got to messing with the ScanGuage and found a field called LOD. It seemed to indicate engine load and was a pretty good indicator of when the shift would occur. It reads between about 15 and 99. Anytime it read above 93, it would downshift. This seemed pretty consistent, and as I kept a steady foot on the gas going uphill, I could see the numbers climb until they reached 93 and then she'd downshift and run up over 2 grand and I'd lose 2mpg.

I then carefully watched this LOD readout, and as it approached 93 I'd let up on the gas. Sure enough, she'd hold off shifting, and even though my speed dropped, my MPG's didn't.

After doing this for about 200 miles, several things came to light.
1 - I regained the lost art of non-cruise control driving. I could accomplish what I wanted by the sound and feel of the van.

2 - The van seemed to learn as well. I could now take the LOD reading to 99 and even keep it there and she wouldn't downshift unless the road got steeper or I stabbed the throttle..

3 - Due to my now second nature ability to keep her from downshifting, I'd occasionally find myself going 30 mph up hills on the interstate where the minimum is 40. Simple solution was to set the cruise control at 42 mph and while I was daydreaming with my foot letting up, she'd downshift on her own to maintain 40, but at that speed the downshift only puts her at 1,900, and I'm still getting my 8mpg.

Funny, I used to be interested in how fast I could go but today being a retired old dart pulling a Big Big Duck, I'm more interested in how slow I'm allowed to go.