Alasdair, your oil burner is a bmw engine, the 200/300 tdi in the disco is crap, thats all there is to it. V8's are ok in water as long as you have good leads and work the dizzy properly, there is two drain holes in the bottom yu need to block one then ue one to suck air through into the brake vacum hose via a new intake breathe hole in the side of dizzy from airbox, seal the cap with silicone, it'll be ok as you wont need to keep removing to spray with WD40 once done properly, my V8 was fine submerged, to the point that my airbags were soaked lol. but 17 mpg?? not if you have decent off road rubber, running the simex i had on mine it did 7Mpg, and even on a decent run it only did 9 :o . If you want great noise plus power, look at fitting subaru legacy 2.5 twin turbo motor at 285 bhp, or convert that to lpg too which will give circa350bhp properly set up, or 450 bhp set up for E85
I'm looking at putting one into a suzuki SJ soft top. 450 bhp in a car weighing a ton ready to go with winch etc, thats gonna be a scream, in more ways than one lol