Rusty dipstick tube

When I check my engine oil, I find that the top 3/4 of the dipstick is covered in surface rust. There's also usually some rust residue on the bottom of the dipstick too (where it rubs on the tube when you pull it out). I'm positive the oil pan is clean, and that the residue and rust is only in the dipstick tube.

Is the dipstick tube removable? What's an easy way to clean it out with out polluting the oil?

88XJ 4.0L

I don't know on your 88, but on 91+ (should be the same) the tub is secured with one bolt to the block and a tight fit in the block. It can be removed fairly easy for cleaning.

Thanks, I'll look at it more closely tonight. The bolt is probably covered with road grime.

Crankcase oil draws moisture from the air (most non-marine lubricants do). That is one reason for the "3 months or 3000 mile" oil change intervals. Moisture in the oil combines with other contaminants and that can damage bearings.

If you are changing your oil frequently enough, problems in the CCV system can aid in moisture build up in the crankcase.

Once you clean the tube and dipstick, see if you can identify the cause.