I have a 96 F350. Right now I use valvoline 15w40. I change it every 3 months or 3000 miles which ever comes first. If I were to change to synthetic how long can the oil stay in the engine. I do not put to many miles on the truck anymore. The amsoil site says 1 year, is that ok. Also my brother uses valvoline synthetic 5w30 year round. In his 99 f250 powerstroke, Is that good for the engine? Thanks.
I can't relay anything on the Valvoline, but I can on the Amsoil. Typical oil life with Amsoil sythetics and Amsoil oil filters is 15k miles or 1 year, which ever comes first. The reasoning behind the 1 year max is condesation. If you have a truck that rarely drives or only drives very short trips, condestation can build up in the crank case and we want to get that out. If you drive it on long trips (20 miles or more) every now and again, especially towing, this is not so much of an issue as the oil and motor get warm enough for the water to vaporize and be expelled through the crankcase breather system. Still, once per year to be safe. If you use oil analysis, you can monitor the water content in the oil along with many other contaminates, and extend the fluid changes out until a sample comes back saying it needs changing. Filters should be changed every 15k or 1 yr still. Does this answer your question?
