Royce,
By now all are sick of my too-long diatribes on oil or engines. Sorry. I did
forget the weight of oil you asked about for the 4.0 Wrangler. Sorry. The
short answer is, read the owners manual. The engine got better and was
machined better as it improved each year. You did not say what year yours
is.
No modern engine can tollerate a straight-weight oil. Use the old single wt
oils on our vintage muscle beaters. Thicker can be better in the hot summers
and older worn engines even in multi-grades, especially in extreme service
of trailer towing, but never in engines since about the year 1994. The newer
engines, especially since about 2000, must move oil fast, super fast in
extreme service. The tolerances are too tight for thicker oil than what is
in the book! So if it says 5W15, do it! Never use oil additives in modern
engines. Thicker is not better on newer engines, but in fact will cause
destruction. Oil keeps an engine cool. Low oil levels make oil hotter.
4,5,6,7,+ quarts are not necessary to keep the engine oiled, but absolutely
necessary to keep the oil cooled.
Forget the recommended 5K to 7K change intervals. It is marketing hype. If
you want your engine to really last, you have got to get the trash out. Oil
does not and cannot wear out. It gets dirty with abrasives of burn't fuel
and dirt (Fuller's Earth). 3K miles is a good target goal. The oil filter
will not clean it out or remove it from the oil pan. Only changing does
this. If you could centerfuge or filter-clean your own oil, you could reuse
it since you know the weight and grade. Neither are cost effective. Engines
running on propane VERY seldom need oil changes and are incredibly life
extended.
Even an inverted filter pre-soaked, and drained, is better than installing a
dry filter element when you cannot install it pre-filled. You do not want
your engine running without oil while the new filter is being filled and the
paper element purged of all the air bubbles. The cost savings, not stripping
or over-tightening the oil plug, and prefilling the filter is your
justification for the do-it-yourselfer. It is hard to find a dealer, shop,
or lube center that will care about your vehicle, what goes on it, in it, or
how it is done, like you would. That is sad.
When you buy a filter, check for score cut lines on the box or metal side. I
have much experience with stock clerks cutting every filter on the out sides
of the case with their box cutters. If the thin-walled metal is scored
beyond the paint, it will almost always fail in use, but not immediately.
-Eddie- Houston, Texas