We have a Ford 172 diesel, an AC D17 diesel, a 6 cylinder Perkins, a 6.5L TD in a Suburban and a Ford Powerstroke and each one has a slightly different "aroma" when idling. The old AC probably has the lowest compression ratio so it has the richest exhaust. The Ford 172 probably comes in 2nd. The two vehicles are pretty close, but the Power Stroke has a richer smell, especially when cold. But as some of the other posts mentioned, several factors affect diesel combustion and the exhaust smell--fuel quality and type, compression ratio, injector timing, injector condition--especially the atomizer tips, fuel pump timing, piston blow-by, valve seating conditions, air inlet filter condition and type of oil. I've noticed that two identical tractors and condition--one using Rotella and the other, say Delo, will smell differently. Since a little oil gets burned with diesels, that enters into the mix too. This is more noticeable right after changing the oil--it becomes less and less noticeable after the engines get a few hours on the oil change.
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