genesbro

Don't do it, if you want to run 5w-40 that would be ok but don't run with anything other than 5w-something. The first number has to do with the size of the oil molecules and if the engine is not designed for a 15w- oil you could cause serious damage due to the oil not flowing where it needs to flow to.
I run 5w-30 in mine, Mobil 1, and it does not make any noise even when it has sat during my recovery.

Dronac

The "w" number is winter weight. It's the viscosity of the oil on cold starts (at the current temp. In a very cold environment, 0w-x would be better. Unless it's nice and hot out, I wouldn't put 10w-x in my engine.

JKlad

Got this from "Machinery Lubrication" website, in a discussion of why auto manufacturers are specifying thin oils with low levels of friction-modifiers (these pevent engine wear but potassium, the main component, reduces the life of cat converters) now days in order for them to pass the federally mandated fuel consumption and emissions tests, even though these thinner oils don't hold up as well and produce greater engine wear than thicker oils:

"What To Use
Although thinner oils with less antiwear additive outperform more robust products in the 96-hour fuel economy test, it is not clear that such products save fuel over the useful life of the engine.

Every fluid is a compromise. Oils recommended by the auto manufacturers seem to compromise protection from wear under severe conditions to gain fuel economy and catalyst durability. It is important to recognize that to use a product that offers more protection from wear will most likely compromise your warranty. Thicker oils also compromise cold temperature flow, which may be of concern depending upon climate and season.

The best protection against wear is probably a product that is a little thicker (such as SAE 10W-30 or 15W-40) and has more antiwear additives than the oils that support the warranty. The best oil for your vehicle depends on your driving habits, the age of your engine and the climate you drive in, but it is not necessarily the type of oil specified in the owner’s manual or stamped on the dipstick."

As I live in a hot climate, I need a thicker oil that will hold up at high temperatures and do not require a low winter weight oil as ambient temperatures where I am never approach freezing, even in winter. 5w20 isn't even available where I am off the shelf for this very reason, 5w30 is available but is very expensive as it is considered a racing oil for winter applications. From what I've been reading, 10w30 or 15w40 it is for me then when my warranty's up. Also, they achieve the "5" winter rating by adding more chemicals to stop the wax in the oils thickening at freezing temps (kinda like taking aspirin to thin your blood); it's still the same base stock as "10" winter oil so the molecules are the same size. In the same way, they add other other chemicals to give the oil a higher hot temp weight (ie SAE30 as opposed to 20).

http://www.machinerylubrication.com/Read/518/motor-oils

It's not only the US manufacturers that are doing this (specifying thin, low additive oils to meet mileage and pollution targets at the cost of engine longevity); a Mercedes mechanic was telling me recently that they're having all sorts of issues with their motors these days regarding high oil consumption and premature engine wear, and this has coincided with Mercedes moving to these thin oils with low levels of ant-wear agents to satisfy the regulators. It's certainly no coincidence also that the 3.8L V6, which had a long and trouble-free history in minivan applications has suddenly gained a reputation as an oil burner and a motor prone to premature wear (there's got to be literally hundreds of threads on this site if you look, dealing with spun bearings, oil burning motors, collapsing valve-trains, etc; all symptoms of incorrect and insufficient lubrication). Here's a link discussing this (see the heading half way down the page "The question of phosphorus"):

http://www.upmpg.com/tech_articles/oil_bottle.htm

Denny2565

Well, I can now say that the Mobil 1 filter is worthless. Putting in 5W-30 got rid of the running engine knock, but I still had the start-up knock. I always used Wix filters in the past and decided to replace the new Mobil 1 filter with a Wix.

Previously, whenever I removed the Wix filter, I would get a little stream from the bottom of the filter when I broke the seal and a short gush of oil when I pulled it away from the threads.(the gush that hits the axle every time) There is also some oil left in the filter that I have to pour out.

I broke the seal on the Mobil 1 and got a small stream of oil for a few seconds. But when I pulled the filter away from the threads, not one drop of oil came out. And when I tipped the filter over, there was no oil in the filter other than what was in the filter material itself. So the anti-drain back valve either didn't work, or there wasn't one in there at all. Either way, my $32 bargain synthetic oil change has now cost me over $80. The next time, I'm going with what I know works.

TINMAN080

I've put 950,000 miles on various vehicles since 1987. 3.8 GM, 4.3 GM, 2.8 GM, 3.5 GM, 2.5 Jeep, 3.8 JK. ALL run on 10W30 Pennzoil Dyno. ABSOLUTELY NO issues. No engine repairs WHATSOEVER. NO oil usage at all, on any of them. I don't abuse my vehicles, but I buy them to DRIVE them, and I DO. my JK has 52,000 miles, about 45,000 at 75 mph on a regular 120 mile daily commute. Always have used Fram cheapie filters, around $3.00-3.50. No drainback issues. This combo works for ME! Avg 17.2 combined....

Rhino64

I live in a hot summer environment not uncommon to see low one hundred deg. days and have used 5-20 with no issues.

5150cliff

That comment is very probable. I purchased 2- 5 qt jugs of Mobil 1 from Auto Zone recently and when I opened the first, I saw a very small tear in the foil seal. As I poured some into a jar, it looked funny, like cheap oil. Upon opening the second container, it looked like the synthetic stuff. I took the first one back and replaced it and the guy told me that it's common for someone to buy a jug of the high dollar stuff and use it, only to fill that jug with cheap oil and return it for a refund saying they didn't need it. The criminal did a pretty good job of sealing up the jug to look like it was un-opened. Open the caps and look while in the store.

river2c

You did add 6 quarts of the new oil didn't you? Always check you're dipstick level after you add new oil. Castrol Synthetic 5w20 should work fine.

Denny2565

Yea, I actually bought an unopened box of six, I just paid full price for the sixth one.

FrankTheTank

From what I've read, Castrol Edge Full Synthetic is supposed to be their newest and best oil yet. Anyone else have experience with it yet?