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Thread: Oil Question?????

  1. #1
    aamusls06's Avatar
    aamusls06 is offline Cadillac Owners Fanatic
    Automobile(s): 94 Cadillac Seville SLS, 88 Cadillac Deville, Trailblazer SS
    Join Date
    Mar 2006
    Logan, OH

    Oil Question?????

    Ok. I bought my 94 Caddy SLS in april with 113,000 miles and changed the oil at the 114,000 mark. I used Castrol 10W30 high mileage oil. I've had alot of experience with Castrol from having it in a car that was driven over 500,000 miles(Castrol 20W50) and in our John Deere Diesel farm tractors. I also run the 20W50 in a 88 Cadillac 4.5 Deville that seems to be responding well to it. Over 180,000 miles on it.

    Here's the question, I want to switch to a synthetic blend of Mobil Oil. What would be the best weight for a N* with 119,000 miles. I fear running heavy oil in the N*, because I just don't trust it like the older motors I've ran 20W50 in.

    What do you all recommend?

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  3. #2
    Elmer Fudd is offline Cadillac Owners Fanatic
    Automobile(s): 99 Deville Concours
    Join Date
    Jul 2006
    Tuscaloosa, Al.

    Re: Oil Question?????

    When in doubt, go by what the manual says. Mine (99) says 10w30. There is no note that says to switch to something else over 100k. There IS a note that specifically says not to use any other oil than the two recommendations (10w30 and...........eerrrr I forget, the lighter stuff,.....5w20??, whatever....but that is reccomended only in very cold climates).

    Anyway, by 2 cents is to stick with the heaviest of the recomended oils. Maybe someone else has more knowledge on this than I......

    And I would get Mobile 1. I drove an Old Town car 3 miles with a snapped oil pump shaft before the lifters even started to make any noise. NO engine damage at is WORTH THE $$$.

  4. #3
    krimson_cardnal's Avatar
    krimson_cardnal is offline Cadillac Owners Enthusiast
    Automobile(s): 96DeVille
    Join Date
    Aug 2005
    NY Capitol District

    Re: Oil Question?????

    13W40 Rotella - search it out in this forum. This is the bottom line, however.

    No need for synth. Follow the cars oil change display. AC filter. Never over-fill.

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with DTS floor shift)
    Join Date
    Jun 2004
    Woodstock Ill.

    Re: Oil Question?????

    119K is not high milage on a Northstar. It will run forever on conventional 10W30 . Many poster here have over 200K and a few over 300K on conventional 10W30.

  6. #5
    JohnnyO's Avatar
    JohnnyO is offline Cadillac Owners Fanatic
    Automobile(s): '99 Eldorado, '04 DeVille
    Join Date
    Nov 2003
    Pittsburgh, PA

    Re: Oil Question?????

    If you use a syn or syn blend, just get the same recommended weight of 10w-30. As far as I know, Mobil discontinued the high mileage blend, at least I don't see it on the shelves anymore and I used to use it. Actually Valvoline Max Life is about 30% synthetic although it is not marketed as a blend.


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