don't go below a 30 weight oil in our engines - it's not designed for that low of a viscosity. Also don't recommend the 0W oil if you have any leaks, since they will become worse at cold start with a thinner oil. I'd stick 5W-30 for our engine's design and age. It's a delicate balance.

 

10W30, 5W30, and 0W30 all have the same viscosity at operating temp. The ONLY difference is viscosity at ambient (room) temp. 0W at ambient temp. is still too thick to properly lubricate our engine. I can't see how an engine would have a cold start leak problem. Perhaps I am reading this wrong. 10W takes longer to lubricate the top end of ANY engine than 0W.

0W30 will reduce start-up wear more than 5W30. 5W30 will reduce start-up wear more than 10W30.

The old thinking behind oils and weights doesn't apply to modern oils. Especially the synthetics.

The leak issue is a myth. Viscosity is viscosity. Dino or synthetic, if there's a gap, it will find it. The ONLY possibility of developing leaks with synthetic after using conventional oil is where the sludge from the conventional oil is washed away, revealing wear that you already had. No NEW wear is created by molecularly perfect oil.

There is a great independent study that tested Mobil1 and Amsoil over ever increasing mileages. Bottom line, they both last well beyond the 3,000 mile mark, (Mobil1 18,000 - Amsoil 14,000) with only a filter change at about 7,000 - 10,000 miles.

 

Dukie, I see your high mileage on your XJ. I attribute that to you being a good owner. I have to wonder what climate you live in? I'm just curious. I live in N. Illinois. I suffer the extremes.

I have a 249,000 suburban that doesn't have a tick. I attribute that to mobil1. (I can't believe I just admitted to owning a burban.)

It's my wife's DD, and I have often found it low on oil and generally neglected. I change its oil every 10-12,000.

Keep on.

 

Yes yes!!! Oil is all very close to same thickness at operating temp and all oil is too thick at room temp.... hey Btw do you know.who that guy is??

 

I wasn't saying that the lower ambient viscosity caused leaks. Any engine has larger gap tolerances when the metal is cold. Our engine tolerances are larger than those of say the high compression engine in my Acura (which uses 0W-20). Thus it is more prone to leaking at engine joints when cold, regardless of seal condition. As the vehicle ages, these "gaps" get larger simply due to engine wear. This is why I made that statement - I prefer a little more viscous oil to keep cold leaks to a minimum.

I live in a mixed climate (Baltimore, MD), where we have both hot and cold extremes.

 

Who?

 

The tolerances in engines are different... by 2 or 3 thousandths maybe. If you read the article posted you will realise that even the lightest oil made for motors is too think cold. That is really all the 0 is referring to. And the climate does matter once the engine has warmed up but in a cold climate you need lighter oil anyhow. At operating temp a 40 weight oil will help larger clearances a little. Put it this way, I run 10-40 in a 150000 mile original 289 from 1966 and it does the job well... you really think my jeep needs oil that is thick enough to keep the 289 quiet? I'm a Machinist and have rebuilt motors so I know about tolerances and wear.

 

Guy that wrote that

 

I've read that article many many times and always recommend it. I'm well aware of what it says.

 

Stick to 5W-30 in the winter and 10W-30 for the summer. Unless you're paranoid, then you could use five-thirty in the summer, too. Has anyone done the upgraded oil pump in the 4.0 yet? How much would it cost and what would it involve?

 

Not really necessary. If you want one they're not expensive and its a fairly easy swap just make sure you get the hardened drive tube. Im running 0-30 synthetic.

 

http://www.bobistheoilguy.com/ Great info. VERY detailed. Multiple articles.

http://neptune.spacebears.com/cars/s.../oil-life.html This is from a group of enthusiasts who performed their own tests and employed blackstone labs. While their methods are less than scientifically 'perfect', they're better than I could have done. Unbiased and just looking for some answers. Scroll to the bottom of the first page to see the links for the results of their Mobil1/Amsoil comparisons.

ENJOY!

 

Cot damn oil thread came back

 

Hahaha.