Here's what i think.

Sludge build up.


And yes that is MY motor

 

Holy crap!Not sure if I've ever seen anything that bad, lol.

 

Yep, try takeing the motor apart JUST to clean it so it gets oil. Not fun. I was black for 3 days...

Also the valve cover was so packed the rockers wore a place in the sludge...

 

Oh my God dude, did it actually run???

 

What's the story behind that? Years of neglect or what?

 

Nope when I first got it it was over heating, so I changed out, water pump, and such and no help, the po used one bottle of that stuff every oil change and when I desired it had to be in the motor I found that... And yes it runs, still pulls tires when second locks in lol

 

ive run the cheapest 10w30 with no additives and no issues.

and now rotella 15w40 in a high milage motor, (cheap and still looks good after 4k miles) also no issues, no sludge buildup.

 

I like it. It took away a tick in the motor and is suppose to prevent dry starts.

 

I had considered Lucas Oil at one time but, was warned that if my oil pressure is already good (pegs out at 80 when it's cold and only drops to about 40 at idle and full operating temperature), it has a strong chance of blowing your rear main seal.
I ran the Shell Rotella T full synthetic in my 25 year old motorcycle for years (specifically because it had a wet clutch and I couldn't use anything with friction modifiers in it) and it performed exceptionally well so, I may start using it in the XJ.