I always ran my vehicle down to a gallon so that there is no accumulated junk build up. The fuel pump is cooled by the fuel flowing through it. Fuel sitting in the tank for months on end deteriorate into harmful products
The 1980 diesel rabbit had a top gear that required the engine to spin at 3500 rpms to go 60 MPH. the 82, 83, & 84 diesel rabbits top gear the engine spun at 2300 RPMs at 60 mph. That was the big mistake of the VW Rabbits that let Japan into the USA market
I am use to 40-50 mpg on my vehicles, 77 gas rabbit, 83 diesel rabbit, 64 diesel rabbit, 86 civic, 92 5-speed 4-cylinder caravan, 01 prism, 11 cruze, 18 cruze, 24 maverick hybrid
if it is just 2 of you then putting water jugs on the rear seat floor is even better. Pack the rear seat with heavy items helps. More weight in the truck give more control.
My brother bought a 24 foot box camper with the mercedis 3.0 liter turbo diesel engine and tows his chevy spark . he get 14 MPG at 65 MPH level interstate
Attach it to a custom made tonnel cover and you can store heavy stuff in the bed in front of the rear wells to keep some weight out of the trailer. the stationary piece of the tonnel cover would probably be the center piece.
I am averaging 45.7 (MPG gage) from day 1 on my hybrid for 2 years June 10-2024 to June 11-2026. I live in zone 6 USDA Cincinnati, Ohio. My MPG read about 5% higher than calculated. I run 42 PSI front tires 35 PSI rear tires. Front end is heavier.