First of all, I'm now officially obsessed with this site, and I love it. ------------- I've been reading a lot about the Delvac1 5/40; It has a visc. of 15 cSt @ 100 deg C Has anyone used this a in a new engine which has tight clearances? is there any danger in putting this oil in a 4.6L Ford(97)modular engine, which is supposed to have rather tight clearences? BUT it has 87,000 miles on it, and I think the it probably doesn't have the same clearences as when it was new, right? Also: how much of cold start-benifit am I giving away if I used this oil in such an engine? Can the detergents in a "fleet-oil" like this be harmful to a modern gas engine, which demands API SL rating? (I think delvac-1 5/40 is SJ rated for gas engines...) I'd really appreciate some answers from people who have used Delvac 1 in new or relatively modern engines where a much thinner oil (5-30/10-30) was recommended by the manufacturer. Thanks a million!