Also, when you run your engine there is nothing between diesel exhaust and your living quarters except for a thin, leaky, single paned window (unless your exhaust from above in which case your get exhaust in your face as you cruise). You are going to smell some engine/exhaust smells no matter how well you maintain your engine. Some people may have gotten used to the smell over the years, also as we age our sense of smell dulls. I just can't see a way that it isn't a factor. I really wish I could easily and reliably access HVO bc I think the smell is less.