cruiser54

Correct.

We used 15-40 at the dealership here in central Arizona for years. Never had a single one blow up. Gimme a break.

Klutch

I'm certainly no diesel engine expert. But I do know they're a completely different animal. It's not just a gas engine with high compression. In fact, GM tried to convert gasoline V8 engines to diesel back in the 1980s by boosting the compression and adding fuel injection. It was a miserable failure because the rotating assembly couldn't handle the extreme forces of a diesel. Not long after these cars were new, the engines were shot. You've likely never seen one of these cars because they were junk and were soon scrapped.

FYI, the first number in an oil rating is the PROTECTION the oil offers when it's cold. And when a gasoline engine is cold, it needs an oil that will flow well and get to where it needs to be. It does NOT need a heavy oil which will provide a "film". (And that's not what a 15W does anyway.)

Thus, a 5W-40 oil provides the PROTECTION of a 5 weight oil during cold start and the PROTECTION of a 40 weight oil at operating temperature. A 15W-40 oil provides the PROTECTION of a 15 weight oil at startup which isn't nearly as good as 5 weight protection. So, why would you run a 15W-40 oil when 5W-40 and 10W-40 is readily available? It's possible, but I've never seen a gasoline engine where 15W-anything was recommended.

Manufacturers put additives in the oil to give it these properties. They really are pretty amazing despite what luddites might suggest when they say, "I don't like these multigrade oils". Then they typically talk about what people run in race cars. And what people run in race cars has absolutely nothing to do with what you should run in a street vehicle. Here again, a racing engine is a completely different animal.

jld66

i live in maine and this febuary we constantly had 0 to minus 0 every morning. in fact the coldest on record. i run plain 10-40 with a napa gold filter. change it every 3000 miles on my old 97. when it was -15 out or below that, started fine. the oil light stayed on for a few seconds longer but had no problems.

Klutch

As I said above, it's not like engine parts are going to come blowing through the hood. But in Maine, you really should be running a 5W, or even 0W, in winter. It's better for your engine during cold starts.


It's like trying to tell someone with 10,000 miles on their conventional engine oil that they really should change it. He might say, "Well, it's running fine. I don't see the problem". Engine parts likely won't come blowing through the hood, but many miles down the road, he's blowing smoke and burning oil.

Klutch

Key words: "central Arizona". 15W-40 would be OK where it doesn't get very cold. Where it does get cold, 15W is less than optimal.

bigbadon

The Jeep 4.0 is very similar to a diesel and there have been thousands of them that have made it past 300k on 15-40 and all types of oil brands and weights. The 4.0 is as close to a tractor or industrial engine as you can get. Most farmers run 15-40 year round. True it takes a slight bit longer to flow but. I have torn down engines that have sat for months and there was always plenty of oil on the journals and in the crankshaft cross drilling. The thicker oil does affect economy (a bit). If temperatures were consistently below 10 degrees I would have 2nd thoughts but that is rare in most of the country.

tzaracki14

Living in nebraska I think I'm gonna try running 15w40 during the summer and 5w30 during the winter .. My 4.0 has 200000 on it and I think she will appreciate

cruiser54

Central Arizona means 5000 foot elevation and 0* temps in winter along with 100* temps in summer.

Ever see this?

Jeep Engine Oil Viscosity

This was taken from pages 82 and 83 of the 1989 Chrysler/Jeep owners manual.

Selecting Engine Oil Viscosity

When changing or adding engine oil select the proper grade by using the chart on the following page. Select the grade that corresponds to the ambient temperature range you expect to encounter before your next oil change.

30*F to 100*F+ 20W-40 or 20W-50
0*F to 100*F+ 10W-30 or 10W-40
-20*F to 60*F 5W-30

sycoglitch

Ha, gotta love the old books. Never will you see that in the newer ones. Wonder what asain warner specs, unless chryco actually put that originally until they said only 10-30 and 5-30

Klutch

No. I've never seen that or anything like it. Were you looking at an actual owner's manual which lists exactly what you wrote above? Or, did you copy it from another forum, or something? I don't mean to criticize you, I'm just skeptical a vehicle owner's manual would actually recommend such heavy oil. My 2000 XJ oil recommendations are NOTHING like that.

sycoglitch

Read what i wrote. First, cruiser wouldn't make that up, second, in 2000, chryco was already making their own standards for an engine that wasn't theirs. At least during the renix era, the engine wasn't too far away from where it came from. Meaning chryco wasn't at the point where 5 other companies had owned them and they were just moving stock and trying to meet new federal emission numbers.

StuckBuck

Mines got 204000 on it and I have always used chevron brand 5w30 with wix filters, got down to 2 degrees This winter in oregon and didn't have any problems, never have!

93_xjcherokee

I run rotella 15/40 and have no issues.

dmill89

^This, over the production run they spec'ed lighter and lighter oil, primarily for fuel economy reasons. They did this with many other engines too, it is one of the reasons that most 07-11 JKs with the 3.8L V6 (and other vehicles with this engine) burn oil like crazy, Chrysler spec'ed 5w20 for them, but the 3.8L was designed in the 80s (I believe they originally spec'ed for 10w30) and did not have the tolerances to handle oil that thin without burning it at a higher than normal rate (at least what most people would consider normal, according to Chrysler and other manufactures up to 1qt. every 500 mi is "normal").


Honestly the 4.0L I6 isn't exactly picky when it comes to oil and will generally run for a long time on just about anything that says "motor oil" on the bottle, though some oils are definitely "better" than others, 15w40 should be fine as long as temperatures are above freezing (the temp chart crusier54 posted should be a pretty good reference for temp/oil viscosity).

cruiser54

Yes. It's a direct quote from the owner's manual.

I was Service Manager and Shop Foreman at a Jeep dealer from 1980 til 1992.

That's what's backing me up when I respond to your posts.

So, who is speaking from a factual position and who is just throwing crap out there?