cars are pretty hard to truly fuck up. theres insoluble metal shavings all up in many older cars, the oil, the gas tank . big chunks can fuck shit up but wont happen with suggested means.
short of water locking the engine to where it cant turn over or frying all the elec and other major disasters it wont really be done for, a heavy oxidizer will clog channels for coolant etc, much more efficient . i have a friend with a protege that has the spark plug out open for any crap to fly in for example, still running even if it dies at idle. one of my cars has 12:1 compression ratio, very high tolerances, some 2000lb per square inch being "directly" injected. thats a pretty different monster than older cars. so that will make a difference
anyway good luck.
to be honest fires work the best