Matt, one possibility is start adding M1 15W-50 or Delvac 1300 Super 15W-40 as you continue to add oil during this interval. The M1 probably won't thicken up the low end as much as the D1300S will. (Some folks here have said the 15W-50 has a low vis closer to a dino 5W, while Mobil says the D1300S has a low vis close to a standard 10W.)
The advantages to adding M1 15W-50 are that you keep it all full syn & you get a bit more anti-wear additives (according to Mobil's info). The disadvantage is that you may not be adding too much vis into the low end, & you will thicken up the hot end a bit.
The advantages to adding D1300S 15W-40 are that you'll keep the hot end at a 40wt while adding more vis to the low end, & you'll get more anti-wear & detergent additives. The disadvantage is that you don't keep it all full syn anymore. Actually, with the other benefits of the D1300S, I think I like this option better than staying full syn by adding the 15W-50. (Hmmm, I like this idea so much that I think I'm going to start doing this on my 10k/2yr M1 15W-50 test-case car!)
Then, on you next change you could mix 50/50 M1 0W-40 & D1300S 15W-40, & continue to top up with whichever makes you most comfortable at the time (0W-40 Oct-Mar, 15W-40 Apr-Sep?).
[ March 03, 2003, 03:57 PM: Message edited by: Greg Netzner ]