I'm about to change the oil on my D1 and was wondering if any brand was preffered, and also the optimum viscosity to use. I'm taking it to Vermont next week and that's where it will be until next summer... so it will probably be getting into the 30's and 40's (temperature wise) before my next change

 

The oil is important but even more so is the filter and the frequency of oil changes, every 3000 miles.
10W/30 oil for where your truck with be, I am a big Castrol user myself. As for the filter use either a K&N 3001 or a Mobil 1 oil filter.

 

Mobil 1 or Amsoil Synthetic will both last significantly longer (and not just longer, the degradation curve is much shallower... mineral loses a lot very quickly) and give protection for much longer including if the engine temperature goes higher than normal as synthetics resist thermal breakdown much better than mineral. I've always run Synthetics and any vehicle I've owned from new has lasted despite my being rather rough with them.

 

ajh- I run Rp and synthetics do last longer, but in these trucks, I wouldn't pass the 5K mark. Lower on higher mileage. These run so rich, you get way too much fuel and carbon in the oil. I ran an analysis and at 7K I saw high figures.

The filter is the problem. I know several truckers who have tripled their drain times with RP, and one who went 100K on the oil with a ceramic bypass and changing just the regular filter twice. Oil is still good, just gets to dirty normally...

 

Rovers run too rich for long duration oil changes but here is a really neat oil filter to help out.
http://www.rpmoil.com/index.php?main...index&cPath=14

 

Synthetic Castrol, but only the German made one. I have used it in my other car for 7 years. Of course it's 0W/40, but they also make the German Castrol in 10W/30&40, but not easy to find.