Rotella T6 5w-40 - Jeep 4.0 ZJ 253,000 miles

Mar 11, 2016
Denver, CO
Here is the Blackstone report for my 1996 Jeep Grand Cherokee 4.0 engine with 42RE A/T with 253,000 miles at the time the sample was taken. I was using a Motorcraft FL-1A filter and a A/C Delco stock paper air filter. This is for 3,000 miles with around 150 miles of those being off road in dusty conditions and 2,300 miles towing my camper.

I had been doing 5,000 mile intervals with the T6 but after finding metallic particles in the bottom of the drain pan I started doing 3,000 mile oil and filter changes. The particles were non magnetic and the larger ones (about 3-4) about the size and shape of pinky fingernail clippings and looked aluminum along with less then 1/8 of a teaspoon of bronze colored glitter. I have seen these particles in the last 4 or so changes. That is what prompted me to get the analysis. My thinking is the aluminum is from the original timing chain (stretched) scraping the cover when driving at high RPM (for a low reving 4.0). The bronze bearing / babbit material is what I am more concerned about but neither are good.

I run 32” tires and have re-geared the axles (Dana HP30 & Ford 8.8) to 4.56 and have added pretty much all of the bolt ons available for the 4.0 except for a CAI - 62mm bored throttle body, newer style WJ horseshoe intake manifold, Doug Thorley header, 3” exhaust with magaflow high flow cat and flowmaster 70 series muffler. I have also retarded the timing 4* with my DRB III scan tool. Even with all of those mods the 4.0 is a dog in the mountains towing or not and I almost always have OD switched off and often have to downshift to 2nd gear on some the the steeper passes ie: the continental divide. This puts the RPMs in the 3,500 to 4,500 range often and for long periods.

I am in the process of building stroker (4.6L) engine to replace this one but with my other projects and hobbies, I am still in the research and gather parts phase. I have torn down the donor engine to a bare block, but that is as far as I have gotten at this point. Part of the reason I got the analysis was to gauge how soon I will need to have the engine ready. I know I am playing with fire using an engine of this age / mileage for such heavy duty service.

Sorry for the long winded post - I wanted to add as much relevant info as I could.

Any input would be greatly appreciated.


1996 ZJ Blackstone Labs - Oil Analysis - Copy.jpg


  • 1996 ZJ Blackstone Labs - Oil Analysis - Copy.pdf
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Nothing to worry about for a worked 4.0

Install a magnetic drain plug.

Keep driving and get that 4.6 built!

No oil consumption?
Thanks for the reassuring input.

No noticable oil consumpion at 3,000 or 5,000 mile intervals after I replaced the valve stem seals and fixed an oil leak at the oil filter housing.