10w40 in N*

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Northstar Engines and System Technical Discussion Discussion, 10w40 in N* in Cadillac Engine Discussion; Is it OK to use 10w40 in a northstar engine? The manual calls for 5w30 and 10w30, but doesn't say ...
  1. #1
    andrewebay1 is offline Cadillac Owners Member
    Automobile(s): Cadillac
    Join Date
    Dec 2007

    10w40 in N*

    Is it OK to use 10w40 in a northstar engine? The manual calls for 5w30 and 10w30, but doesn't say anything about 10w40.

    My car has 70k miles and is a 2000 deville. Will be doing some hard driving the next few days for a road trip. By hard driving, I'm talking WOT driving to pass cars and trucks in two lane highways. Along with a 22hr drive.

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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with DTS floor shift)
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    Jun 2004
    Woodstock Ill.

    Re: 10w40 in N*

    Is it OK to use 10w40 in a northstar engine?
    No. Use 5W30 or 10W30.

  4. #3
    zonie77 is offline Cadillac Owners Connoisseur
    Automobile(s): 94 ETC,97 STS
    Join Date
    Sep 2003

    Re: 10w40 in N*

    10w30 and 10w40 is the viscosity range. It doesn't benefit you to put 10w40 in. 10w40 also tends to sludge easier than 10w30.

  5. #4
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
    Automobile(s): 2002.5 F55 STS - 65500 miles, 2014 Explorer XLT FWD
    Join Date
    Feb 2006
    MD Eastern Shore, Kent Island

    Re: 10w40 in N*

    If I can go to Florida and back twice a year, run the snot out of the car otherwise, do WOT's, and get 3,500 miles to the quart of 5W-30 synthetic in temperate climates, so can you. Your manual recommends 5W-30 in all temperatures and allows 10W-30 above ?? 20 degrees or so. Whatever floats your boat.

    Higher viscosity ratings than recommended have absolutely NOTHING to do with wear considerations in an engine that is not originally spec'd for them. Using them may well be detrimental to engine life.

    It generally costs $$$ to try and outguess the design engineers.

  6. #5
    clarkz71's Avatar
    clarkz71 is offline Cadillac Owners Connoisseur
    Automobile(s): 2000 Eldorado ESC
    Join Date
    Mar 2006
    Fort Lauderdale, Florida

    Re: 10w40 in N*

    If you already have it then it won't hurt anything to use it.

    Otherwise I would use 5/30, or 10/30 in warm climate like Florida.

  7. #6
    JCM1's Avatar
    JCM1 is offline Cadillac Owners Fanatic
    Join Date
    Apr 2006
    Texas & Michigan

    Re: 10w40 in N*

    I've used 15W-50 Mobile One in both my Seville and Deville during the summer months if I know I will be doing a large amount of high speed driving, i.e. to and from northern Michigan and Texas. I've found that at highway speeds the engine seems to run smoother. Possibly placebo effect but it has never hurt anything.

  8. #7
    Zorb750 is offline Cadillac Owners Connoisseur
    Automobile(s): 1997 Eldorado, 2003 Audi RS6
    Join Date
    Apr 2005
    Oakland County, MI

    Re: 10w40 in N*

    You will do no damage to your engine by using a heavier grade oil, as long as it's not extremely heavy. 15w50, as in the above example, is still thinner warm than 5w30 is when cold, so it will present no problem at all.

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