Unfortunatley, I just have an anecdote that this kind of fumigation with car exhaust was done during the war. In the U.S. my grandfather just used cyanide and he had a barn with barrels full of the stuff. It was used in mining and pest control. When we were clearing out the estate we didn't know what to do with it so we called the EPA. They were shocked and relieved that we were getting rid of it.
Btw, the Soviet KW-1 heavy tank and the T-34 medium tank used the model W-2 twelve cylinder diesel engine, a excellent design and remarkably lightweight. This engine had a brake horsepower of about 500 at 1500 rpm. These tanks were available in numbers in 1941-42, and after 1942 all Soviet tanks used this diesel engine. Models built before this, except for the two above, used gasoline engines like a copy of the famous American twelve cylinder Liberty aircraft engine, also used on boats.
A submarine engine would almost certainly be a diesel and huge, usually two engines of over 1,000 horsepower each. There was one model of a German midget sub that was used in small numbers late in the war that had a small gasoline engine due to the shortage of standard 90 horsepower diesel truck engines that midget subs normally used. I don't know about Allied or Japanese midget subs or Soviet submarines.
The 500 horsepower W-2 diesel engine salvaged from a Soviet tank would be a good choice to provide electrical power if mated with a German or other 50 Hertz dynamo. It would require welding a solid frame and mounting a radiator and fan as well as external fuel tank but it would provide a peak output of 373 kilowatts at full load, probably half that for continuous use if the demand was needed. There is no practical way that the Germans could have loaded down a 500 horsepower engine enough to produce lethal carbon monoxide when overloaded like this for a supposed gassing, and it would be very severe on engine life as it would produce copious black smoke. Probably something like this or a diesel engine used to pump water for bathing and delousing was mistaken for a death house. I can imagine that Heckenholt might have named it as though it were a famous health spa, rather ironically, but not for the reasons that Gerstein alleges.
Any gasoline truck or car engine would have done the job. That is exactly what Scharführer Fuchs testified that he installed at Sobibor. But his story has certain technical holes that should have been plain to a rigorous cross-examination. It is the only claim that I know of where sufficient detail was been established so we know that he was definitely talking about a gasoline engine (at Sobibor). Heckenholt supposedly installed the engine at Treblinka and Fuchs installed the electrical system at that camp afterwards.