My initial idea was simply that the MPI is claimed to do 30 mpg, and LPG is about half price.That would work out a whole lot cheaper to run than any TDI i've ever seen.However having looked into it more i am not convinced the MPI is as economical as claimed, and also LPG is closer to 40% saving.Still cheaper to run than a TDI in my opinion.With regard to telling the insurance company about a like for like replacement engine it will not increase insurance and i see no need to tell them.