thank you very much. ive been a royal purple fan for my se-r for years. due to the fact that i and several others have used the stuff with no apparent pitfalls.. i know guys who are using it in their mustangs that are force inducted.(5w-30) and swear by it. so i will try others. thanx for the info. much appreciatedBror Jace said:For places with really wild swings of temperature, consider switching weights. Most engines in most conditions prefer a 30 weight oil ... 0W-30, 5W-30, 10W-30, etc ... Probolem is, these shear down pretty quickly these days. Many will be a 20 weight at operating temp in just 2,000 miles, even some synthetics. Royal Purple's street oils thin out quickly and Mobil 1 starts out thin.
I wouldn't waste my money on the 'fake' mass-market synthetics out there: Pennzoil, Quaker State, Valvoline, Lucas or Castrol. Good mineral oils but WAY overpriced at $4+ per quart.
For extreme use, I am a fan of using the 15W-40 'fleet' oils in high-performance applications. These oils (as a class) have better/more anti-wear, detergents, disperants and anti-foaming additives. Plus, if they shear down some, they'll still be solid 30 weight oils.
My fave is the newest version (Fall of 2004 or newer) Chevron Delo400 with about 200ppm of soluble moly, a powerful anti-wear metallic additive.
Pennzoil Long Life used to have this stuff ... but took it out about 6-8 months ago.
Best method is to try an oil a couple intervals in a row THEN do a UOA (used oil analysis) on a sample to see how it's holding up.
Search this site using the acronym "UOA" to see samples of these lab reports. I and others have posted some here.
Best of luck.