.

In all seriousness, I did change what oil I am using. I used to just buy Castrol GTX for all my cars at the manufacturers recommended weight. Now that I have read Salad's write up I understand what to look for a lot better.

Why do I see a lot of people running 15-40? Seems like it would be hard on the engine on start ups?


This is true. It does take a little longer to circulate BUT there is no evidence of it being catastrophic. Plenty of high mileage 4.0s have given testomonial to that! That 15 wt. residual film is like grease on cold engine parts so that DOES give some lube protection on cold start ups. The real downside is lifter tick until oil flows enough to fill lifters.

Quote: "That 15 wt. residual film is like grease on cold engine parts so that DOES give some lube protection on cold start ups."

No it doesn't do that.

^ Sounds like he didn't read the Dr Haas' information. Tisk tisk!

It does in a relative sense.
Lower viscosity oil flows better when cold. That's the entire reason it exists.
That includes the rate at which it flows off of metal parts back into the pan. Granted there may be little difference between 5wt and 15wt, but there is a difference. The heavier lube will stick longer.
But..that bit of additional oil film longevity is probably less beneficial than shortening the time it takes to get oil flowing again.

It isn't catastrophic in a 4.0. They seem to run 250-300K miles no matter if you use 5/30 or 10/30 or 15/40. Good Gawd, people add Lucas to their 15/40 in these things and still run another 150K. Even then when they do finally die it isn't normally from lubrication failure. It's a piston skirt flaw or head failure.
Might eventually be catastrophic in a more modern motor designed for 0/20 or somesuch.

OK, After over 200 posts: Which oil do I use? ....Har de har....

(Just a little humor. Don't get mean)

The brown one!

I know this thread has been dead for a few days now but would rather revive it than start a new one. I've been reading around other threads and even on Bob is the oil guy website and have seen nothing but good results with Pennzoil conventional (yellow bottle). Even UOA's show great results. so what gives? Why so much hate on Pennzoil? From what I read, Pennzoil is actually pretty good for our 4.0 jeeps.

What hate on Pennzoil?

Looks good. Run it if you like it.

Just a lot of hate on how it's paraffin base (use to be) and how it will sludge up your engine and create waxy buildup. Don't know if any of this is true but from looking at UOA's it performs really

Just a lot of hate on how it's paraffin base (use to be) and how it will sludge up your engine and create waxy buildup. Don't know if any of this is true but from looking at UOA's it performs really well. A lot say it's the quietest oil they've ran in their jeep.

How about Crisco? Or unsaturated oil?

Here's the deal on that:
Decades ago- think 1920's-30's- most all motor oil came from the Appalachian region. That held true until those oil fields struggled to meet demand and Texas crude gained popularity as a motor oil stock in the 40's.
There were no oil additive packs at the time, OCI's were less than 1000 miles, and engine sludge was a fact of life. All oils caused it.

Texas crude has more natural aromatics like Naptha and less paraffin, motor oils built on those base stocks had slightly less tendency to form sludge.
Oil manufacturers used that fact in their advertising against competitors who continued to use Pennsylvania/Appalachian base stocks- Pennzoil, Quaker State, Kendall....
"Our oil causes less damaging engine sludge..."
Not much later the dewaxing process was improved and detergents started to be added to motor oil, making the difference in base stocks meaningless. But that hasn't stopped the old wive's tales.