I want to go with Royal Purples synthetic blend of oil, so I just want some opinions on what grade to go with. The engine, 5.9L 360, has 117700 miles on it.
My first guess would be 10w30.

 

I've always used mobil 1 15w-50 with great sucess. have never had an internal failure, sludge or any other sort of problems while using it.

 

15w-50 mobil. I'll keep that one in mind. I've seen it available more often than royal purple. I just have a fascination with Royal Purple's additives and what not, not so much for HP gains or anything, just have yet to use it. I guess you could call it an itch.

 

it it's an itch, scratch it lol . the only way you'll know how well it performs is to put it in.

 

I run amsoil 5w-30 in mine and it runs like a champ.

 

Go with the synthetic, whatever brand, its good stuff and will make your engine last longer. I personally run Mobil 1 10w40 in my ram. I run 5w30 in my 03 Liberty Renagade, 10w30 in my 91 Daytona and 5w40 in my 90 Suzuki Katana, all fully synthetic Mobile 1. I would run the Royal Purple but I dont have the bank account to put it in all my vehicles. Good luck with whatever U decide........

 

Royal purple is an excellent oil, 15w50 is a bit thick for a gas engine but you in a warmer climate than most so you should be OK.
I would recommend 5w50 if you can find it. It will flow better than the 15w50 when cold and protect just as well when hot.
If your considering different brand of Syn oil they are not all the same. The premium Syn oils like Royal purple, Amsoil and Red Line (maybe a few others)are in a different league that then the mass market Syn oils. That why they generally cost more. Mobil 1, Castrol Syntec and most others (while still excellent syn oils) aren't as good as they used to be. The term synthetic oil can be applied to just about anything these days so just be aware what your shelling out 5+ dollars a quart for.

 

I use Mobile 1 10-30

 

Be careful, full synthetic motor oil will help you find leaks if your engine has any on a high mileage motor.

 

That's true, but I have never had any problems with amsoil leaking out. My engine doesn't leak or burn any oil, but the trucks at work did. We tried castrol synthetic in one an it leaked all out so we didn't use synthetics.But my boss startedputtingamsoil in them and they don't leak at all now, so I don't know...
and we're talking about high mileage beat *** vehicles here. That's what sold me. I won't use anything else now.