My 1982 vw rabbit pickup has a 1984 turbo 1.6 liter diesel quantum engine in it with a 5 speed eco transmission on it. The exhaust manifold is loose and missing 2 bolts but other then that it runs great I think. I should be getting 50 mpg in it and I'm averaging 30 mpg city or highway trips and I drive very soft. I have the cheapest mastercraft gear oil in it and the expensive 5w 40 mobile turbo oil in it. Why might my mpg be so terrible? What could cause a 40% loss in mpg in a diesel? It sound good and doesn't blow any smoke other then after sitting for a while it blows diesel smell and a little non black smoke out. Pretty grey ish. My number Izmir 8317068926 , any help is very appreciated because I'm about to go on a long trip