Originally Posted by grYthshAde

I live in Saskatchewan, Canada. We routinely see winters that can be as cold as -40C, -65C with the windchill, and summers that can be as high as 40C. (We had -68C [windchill] two days ago, believe it or not. It's days like that where you find every excuse to sleep in and hope that God doesn't damn you to doing something in the freezing hell outside.) I have a 99 XJ Classic, and she has 260,000km on the original motor right now. I've been running Mobil 1 Synthetic 5w30 for as long as I've had the Jeep, OCI of 4 months/6000km. She starts up every time I can't plug her in, and runs well enough for her age. This summer, I'm planning a complete engine rebuild from top to bottom, and I want to start her off right with this new motor. After reading your article, (which I have to say was amazing. Thank you for putting all that together!) I'm pretty convinced that T6 5w40 is a great oil for mild climates, but what about my extreme region? Our weather goes all over the place, and I want Sparta to be happy and healthy all year round. Would you still recommend T6 5w40 for my climate, or should I continue using Mobil 1 5w30 in this new motor?

Thanks so much! As a mechanic's apprentice, I can't say enough how much I enjoy articles like this that are informative and useful.

Originally Posted by Tony_SS

Thanks for the writeup salad.

I have a rebuilt engine with about 1500 miles. Would you say its a little too early for the T6? I run 10w30 Valvoline conventional right now.

Also do you still recommend the T6 in a climate that will experience 5º-100º?

Originally Posted by NCsXJ

I have a genuine question..... A long time back I read an article that oil with weights that are 5w40 or 0w40 are bad because of the viscosity changes the oil had to go thru.... any insight on this?

Originally Posted by salad

Not sure what you mean by this, can you elaborate?

I can only guess that it was an article discussing how Viscosity Index Improvers betrayed performance when used in too great of a quantity tryig to make mineral oil perform like a synthetic at cold temps. Any of the synthetic xw40s is appropriate for use across the entire temperature range. They don't suddenly turn into SAE70 during Spring or something.

Originally Posted by may pop

Everything wears out. They do not say when it has worn out. They make it seem like a week after its in it is no good. Miles or hours are missing from their information.

Originally Posted by NCsXJ

http://www.upmpg.com/tech_articles/motoroil_viscosity/ here it is under the subtopic "Drawbacks" towards middle of page

Originally Posted by salad

Almost got all my data for the requested oils:

Royal Purple 5w30
Royal Purple HPS 10w30
AMSOIL OE 5w30
AMSOIL Z-ROD 10w30
Brad Penn FSGF 5w30
Brad Penn Penn-Grade 1 10w30
Pennzoil High Mileage 5w30

Expect the main page to be updated in a couple days.

As well - fellow Canucks take notice - Canadian Tire has started stocking Rotella T6 0w40! Haven't seen it in person yet but there're apparently 5 jugs at my closest store. I'm excited to go try some but I have 15L of 5w40 already on the shelf and winter is on the way out... hmmm

Originally Posted by salad

Obviously for an oil to be certified under a given API or ILSAC category it must pass certain engine wear tests. These tests are performed on vehicles like a 1996 Buick, not a 1983 rehash of a 1962 design. With a flat tappet cam follower, as opposed to a roller cam follower, sliding forces and pressures at the cam lobe are extremely high. With reduced levels of ZDDP one would assume that molybdenum and boron additives can be added to pick up the slack. However, this is not always the case. Some oils don’t even have them! A good coating of zinc is very important in preventing wear not only during break-in, but to maintain it throughout the life of the engine. At any rate, the SM and SN performance tests are clearly not enough for older flat tappet cam engines:

Originally Posted by belvedere

Again, the Seq. IVA Cam Wear test is performed on an engine with slider-type followers, NOT roller.

Originally Posted by belvedere

Please stop spreading this stuff. In a modified engine with increased valve spring pressures, this is probably a concern. In a production engine? Nah.

The SM and SN tests ARE enough for our engines. Is Rotella a fine oil? Sure. Will other SM/SN oils serve our engines well? Sure.

Originally Posted by belvedere

I don't care one bit which oil you like, or use, but please stop with the misinformation.

Originally Posted by salad

But if you're just reacting to a single poorly-worded paragraph because some ignorants on Yahoo Answers parrot things without understanding it please chill out a bit.