Heavier Oil
 

:( I am confused about the type of oil to use for the type of driving. If I drive 90% city perhaps my oil may have more fuel delution. Therefor A heavier base oil like Delo 15/40 would hold up beter than a 5/30. Any opinions.:rolleyes:

If most of your driving is in city, change your oil at half the time you would otherwise.

If fuel dilution is significant enough to vary your oil viscosity then you have a problem, unless we are talking a 1970 280SE/SL mechanically fuel injected car. In that case fuel dillution could be a factor.