overdue oil change!

my yj is over 215,000 miles and the oil is really mudy, it does not smoke, at all, but the motor feels slower,
is it a good idea to flush or just change?

Thanks for your help!

a flush would be nice. was it ever overheated?

no, it doesnt overheat or smoke is just slugish and im affraid it will smoke if i do a flush


flush what?

Just drain the oil and replace the filter. Do this every 5k miles. Done.

FWIW, I have the 4.2 in my CJ. One of the first orders of business was to replace the valve cover gasket. When I pulled it, it was a sludge fest. I started running Shell Rotella 15w40 due to its detergent qualities, as well as some added protection for the flat tappet cam.

Well, had to replace the valve cover gasket again (been about 3 years), and the head looks clean vs what I started with.

When I first started running Rotella, I swapped filters every 1000 miles, as the detergent in the oil tends to break crap free that could theoretically clog the filter. I wanted to be safe vs sorry.

If your a DD and run this in the winter, its like molasses. Switch to a 10w40 in the winter. I don’t. My CJ only hits the road for wheeling in the winter months.

Most all motor oil has detergent

I used rotella because of flat tappets in my older engines.

The way I flush sludge from my engine:

Substitute 1 quart of marvel misery oil for 1 quart of your preferred oil on the next oil change

Run that mixture for about 50 – 75 miles

Dump the oil

Remove the oil pan and clean the intake screen (because this is where sludge collects)

Replace the pan add your preferred oil

That said if the engine is running slower I would do a complete tune-up on the engine and fuel system.