my cousin has a 98 5.9 , hes running 15-40 shell diesil motor oil in his gas motor , is this going to hurt his motor ... reason i ask is im getting up on milage and wondering if i should go with a thicker oil too thanks currently im running mobil 1 sythetic 10-30

 

i wouldnt suggest it. i run 4 qts mobil 1 5-30 and 1 qt of lucas. the thickness of the lucas really bumps up your oil pressure and keeps everything very well lubed.

 

+1, or 10W30 like the manual suggests. Even then the oil turns darker (like mit is when you perform an oil change) the lucas keeps the viscosity.

I just now became a fan of Quaker state Torque power syn. it was very thin, but with lucas, it makes it perfect and it will keep the viscosity.

I ussually buy whatever synthetic autozone has a sale on. But i will stick with quaker state torque power.

EDIT, my 2001 only has 45K miles on it.

 

On a high milage engine the clearances should be somewhat looser.
I use 15w50 in my 96 with 110000 miles on it.
I have used 20w50 or 15w40 in my 87 since new.
At 171000 miles with no problems.

 

Laramie1997 I know runs 15W-40 Shell Rotella in his truck (even in the winter).

 

Rotella 15w40 will not hurt a gas engine. Just they say its not good for your cat(cause its high in zinc) (Correct me if im wrong)

I was going to use rotella 15w40 in my truck. Still might. You can get 5 quarts for a really good price. I currently run Cas GTX HM 10w30. Should i go any thicker? My engine has around 165,000 on it. Oil pressure is fine. I live in FL. So it gets pretty warm in the summer. Should i go thicker this summer? What would you guys do? Any opinions? Not to hijack the thread, But im sure the info wouldnt just be useful to me.

 

Yes, I have been running Shell 15W-40 for the last two years. No ill effects, and this is the first time I've heard of the oil being hard on the cat....

 

oil is oil.

 

Rotella is High in zinc. That is good for older engines that were built to run on oil with lots of zinc.

The greenies take the zinc out of oil because it produces some gas that can hurt catalytic converters (in their Priuses) and the enviroment. Hence the reduction of zinc in most new oils.

 

I know all about zinc. Just was saying the only thing ive ever heard about the rotella in a gas engine is it being bad for the cat.

I use rotella 15w40 in my dirtbike (03 Honda CRF450R) And its a great oil. Im really tempted to switch to this in my truck.