When Malcolm & Nadine stop for gas, they supposedly get 20 dollars worth, however he only pumps for a few seconds and the pump reads $0.00 showing he got none.
At the beginning of the episode "Novation," when "Donald Kellen" pulls up and parks the black Dodge pickup truck in front of the house in Hillsdale, the engine exhaust clearly sounds like that of a diesel engine. The front quarter panel is badged from the manufacturer as having a HEMI, V8 gas engine, which would sound completely different.