I failed to mention in my earlier post that I also changed oil brands, going from rotella to mobil one. My 83 240 uses very little oil on the interstate running 15-40 rotella.
I would not have ever used 10-30 in that car intentionally during the summer. I had bought it for a winter run up north. I have found switching to 10-30 in winter helps cold starts and mileage, but we don't get enough winter in TN to make it worth the switch.

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1985 300 TD 448K
1984 300 TD 278K

1983 240D euro 240k
1994 f-250 idi turbo 330K
1986 f-350 IDI
1987 F-350 IDI

1985 JD 1050 4wd
1965 IH 3660