Increased pressure is not what made the engine quieter....it was the thicker oil masking the noise! That thicker oil meant less oil getting to the bearings, meaning more heat and wear. It is a noble concept but unless the worn clearances are EQUALLY worn throughout the entire engine thick oil will do more harm than good. First priority for a motor is oil not pressure. Pressure serves no function except to measure engine wear.

 

15w40 rotella

 

If the only variable that changes is the oil's thickness, then oil flow slows down as thickness increases. Eventually, a fluid (oil) could be too thick to pass thru tight tolerences.....at that point oil pressure is great but lubrication is reduced or even stops, and obviously that's not good.

 

1. Filters have valve, so oil is always in bearings, it doesn't drain back.
It is easy to check, oil light should turn off instantly after starting engine.
If it takes a few seconds, oil filter probably has bad valve.
2. Conventional oils lose viscosity, after 2-3K miles 10W30 becomes 5W20, so I think it is better to use heavier oil, especially, if ATF was used to flush engine before draining oil.
Here is my calculations:
If I don't want viscosity to drop lower than 10W30, I need to use 15W40.
But after engine flush there is some ATF left inside, which will decrease viscosity.
20W50 is what I need. (I am in FL)

 

I didn't mean that the increased pressure made the engine quieter. I know the heavier oil did that but the oil pressure increased also. Equally worn clearances? We're talking engines where blow-by was diverted by the PCV hose to a brake fluid bottle mounted on the firewall. Had to get to work though.

 

U really need to educate yourself by reading Motor Oil University starting with Motor Oil 101 thru 109, then take the quiz at the end. U'll then have a better understanding why selecting a motor oil has little to do with where u live.

 

15w for winter? That's terrible.

10w30 for summer, 5w30 for winter. You're running way heavy for cold climate.

 

So, I guess the guys who designed, built, sold, and warranteed these engines didn't know what they were doing when they put this in the owner's manual?



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

 

Progress has been made since '89. Motor Oil University will explain away most of what's in old owners manuals mainly due to motor oil improvements/protection.

 

Since we are talking about oil has anyone heard about the amsoil? It's synthetic and made in the USA and supposed to be good for anywhere from 15-30,000 miles. Well I was just wondering if it's worth the extra money it's 7.55-10.55 a quart.

 

It may be good for 15K-30K miles but any oil will get really dirty/contaminated the longer it's left in. Both conventional oil and synthetic get dirty/contaminated at the same rate.......it's from the internal combustion process and motor condition, not what type/brand of oil.

 

Jeep is a 96 country, inline V6. I always use max life 20-50. You can feel the performance upgrade.

 

Please explain how it's a performance upgrade.

 

Feels like there is more power than when I tried 10-30. Engine sounds better and feels more responsive.

Without equipment, you go by feel.

 

Oh, ok, the old butt dyno, that explains it.........but actually, power is being lost to the wheels as it takes more power to move/pump a thicker fluid than a thinner fluid.....all else being equal.