The long answer is: have the oil analysis done and change accordingly. Many have posted that they show 10k and more between changes is fine by analysis.

Do a search on synthetic oil on the site, should be a TON of stuff on that, empirical and anecdotal eveidence abounds that you can extend your oil changes by double or more, hopefully more, especially with your mostly freeway driving, so the synth works out to be more economical for you than dino.

Short answer: Change every 6-8k.

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1984 300D Turbo - 4-speed manual conversion, mid-level resto

1983 300D - parts car

1979 300TD Auto - Parts car.

1985 300D Auto - Wrecked/Parts.


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"If you don't know where you are going, any road will get you there". Lewis Carrol