Just bought a 84 300 SD. The car has 150.000 miles on and runs like a new car I have a couple of questions, first i want to change the motor oil and was wondering if Shell Rotella 15-40 is ok to use. Its what i use in my Power Stroke. When changing the filter should i pre fill the filter housing? Now for the next question I think there is a vacum problem when the car is under way hot air starts coming out of the vents just enough to notice. This is with the air turned to off. At idle the air will stop coming out.
Thanks for your help, Pete

I use 15W50 in summer and Mobile1 0W40 in Michigan winter...

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1985 300SD
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Rotella T is an excellent oil and is used by many here on the forum (myself included).

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