I've been using 40W, but my truck sits for long periods of time. Last year my wife got sick, and the truck didn't even get inspected or licensed. Today was the first time it ran in over 18 months. Natural oils have a tendency to drain off of critical bearing surfaces over time. Synthetics tend to stay on the parts. Thus the question. I know at one time synthetics were not recommended for older engines, because they tended to cause leakage around old seals. The more modern versions don't seem to have that problem, but I'm looking for Stovebolters who have actual experience using it.
