The owner's manual for my 2001 Disco II tells me to drain and then re-fill the engine oil before removing and replacing the filter; why, and does it make a difference if I take it off and replace when I drain it?

 

You could lose prime on the oil pump.
I have done it both ways doesn't seem to matter.

 

the motor you have will loose prime if setting too long. do this way:

1. Drain oil
2. remove oil filter
3. fill new filter with oil, let it set so you can add more and fill more, 1/2 qrt. or so total
4. put on new filter w/ 1/2 to 3/4 qrt. new oil
5. Make sure previous oil filter gasket is not stuck to block (you would be amazed how many people do this)
6. re-fill block with new oil
7. start engine, run for about 5 seconds, or till the oil pressure light is off, the check oil level.

 

Also make you have the beer iced down prior to service.
This makes the mess that you make of little consequence. [sm=icon_cheers.gif][sm=partyparty.gif]