API grades
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Northstar Engines and System Technical Discussion Discussion, API grades in Cadillac Engine Technical Discussion; ...
  1. #1
    Jan Olsson's Avatar
    Jan Olsson is offline Cadillac Owners Member
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    Question API grades

    Hi everyone!

    Iīm a newbie here so I thought Iīd say hello, proud member of Caddyinfo too I might add.

    I got some questions about oil...donīt wanīt to start another debate here.
    My -93 STS requires 10W-30 oil API service grade SG, but since the current grade is SM I got a few questions.
    Am I right about grade SM being better or at least being equal to grade SG with respect to wear? If that is the case, is it also ok to fill my -88 Eldo with it? My Eldo requires grade SF.
    The reason Iīm asking is because Iīve seen posts about filling 4.9 L with 15W-40 oil with a higher degree of ZDP (ZDDP) eg "diesel oil" to get better protection against wear for the distributor gearing etc.
    Why is it necessary to do that if the grades are getting increasingly "better"?
    Isnīt the backward compatibility in SM reaching down to SF, SG or what?

    Please excuse my bad english.

    Janne

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  3. #2
    chevelle is offline Cadillac Owners Enthusiast
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    Re: API grades

    Your english is fine. Better than my German or whatever.....LOL

    You are correct in assuming that the later API grades such as SL or SM are "better" and , as such, supercede the earlier grades. That is conventional wisdom and is pretty much the case as one of the API requirements is that "improved" performance grades supercede prior grades and are always backwards compatible.

    Having said that.....the current crop of oils "rated for gasoline engines" that are on the shelf in the most obvious locations in the stores are also "fuel economy" oils. Any oil with the ILSAC "starburst" symbol that says "for gasoline engines" is a bit of a hybrid....those oils meet the latest API performance specs, have the minimum allowable ZDP (to prevent catalyst contamination) and have friction modifiers in the oil for fuel economy improvement.

    The difference is that the API specs just relate to the oil's performance as tested on gasoline engines. API specs have nothing to do with friction modifiers or MINIMUM ZDP levels. The API specs just have minimum performance specifications based on actual engine testing.

    Understand that the API performance specs have a lot of requirements besides just "wear protection". Most all of the improvement in the latest grades is in the area of temperature protection. The latest oils will still perform at hotter and hotter engine temperatures. So they are "better" in that the older oils might start to oxidize and give up around 290 degrees F and the latest oils will still function well at 310 or 315 degrees F. They are not "better" in that they give more wear protection.....they just have better high temperature resistence, among other things.

    More modern, current production engines are designed to run with the minimum ZDP oils and friction modified oils. Clearances are changed, designs are changed to add roller followers everywhere that are not ZDP dependent for preventing wear, wear surfaces are hardened where necessary, etc.....

    Older engines designed for the SF and SG oils that had more ZDP in them are not as well protected against ZDP depleted oils.


    So...technically the older engines should be OK with the new SM oils since the SM oils "technically" supercede the older oils and are backwards compatible. But the newer oils probably are " barely" adequate in terms of anti-wear additives such as ZDP. If the engine is perfect inside it will likely be fine. But if the engine is marginal for wear the ZDP depleted oil MIGHT cause a problem and accelerate wear. Certainly you would not want to use the newer ZDP reduced oils for long change intervals in the older engines.

    An older 93 Northstar, for instance, has 32 rubbing element tappets (flat tappets) that require much more ZDP for protection against wear than the 2000 and later Northstars with roller tappets.

    If you want to be sure your engine has the best wear protection you can do two things. One, use one of the non-"gasoline engine" oils such as the diesel Rotella or Delvac or Delo oils. Those oils have much more anti-wear protection since they are also certified for diesel use. The other thing you can do is to spike the oil you are using with extra ZDP by adding a pint or quart of GM EOS (General Motors Engine Oil Supplement). The EOS is available at any GM parts counter and is sold as an assembly lube. It is basically plain motor oil with a high concentration of ZDP that will fortify any crankcase fill with the extra ZDP desired for more anti-wear protection. It is the only oil "additive" I would ever recommend as it is specifically designed for this purpose.

    If you look at the container of Rotella/Delvac/Delo oil you will see in the fine print that it meets all the API diesel performance specs (combinations of the letters CC and CD, etc.) AND it meets the latest gasoline API performance specs such as SL or SM. Now look at the ILSAC "for gasoline engine" oil across the isle in the autoparts store. Read the fine print. It meets the API gasoline SM specs but does NOT meet any of the diesel performance specs. The diesel specific oil is a much "better" product in terms of wear protection if your engine needs it. Diesels have a much greater need for anti-wear protection due to the soot and combustion byproduct contamination of the oil due to the high compression and high cylinder pressures of the diesel engine, so the oils for diesels have to be much better.

    I would recommend the Rotella/Delvac/Delo oils for the 93-99 Northstars, personally. The latest ILSAC fuel economy oils are getting very low in ZDP concentration. Fine with the newest engines on the road but not so fine for a 93 Northstar.

    You can get the Rotella/Delvac/Delo oils in 10W30 for your engine but they are much harder to find. Check a truck stop or large equipment supplier. If all you can find is the 15W40 version of the Rotella/Delvac/Delo that is fine in the 93 Northstar. The oil is not that much thicker to hurt anything unless you live in the far north and need to cold start at -40.

    The other option is to use one of the "severe service" oils marketed by Mobil that are designed for longer change intervals and marketed as such. If you read those bottles you will notice that they also do NOT meet the ILSAC "for gasoline engine" use as they do not have the ILSAC starburst symbol. That is because those oils designed specifically for longer change intervals also have more ZDP in them that excedes the amount allowed for the ILSAC starburst designation.

    I would recommend the conventional diesel Rotella/Delvac/Delo oils. I personally use the Delvac (Mobil) in most everything around the house.

  4. #3
    Jan Olsson's Avatar
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    Thumbs up Re: API grades

    Thanks! Great info

    Feels a bit awkward to use "truck oil" though

  5. #4
    peteski is offline Cadillac Owners Enthusiast
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    Re: API grades

    Yeah, but trucks usually get very abused and most of them have engines which last for hundreds of thousands of miles without rebuilding.

    That's something to think about... maybe it is the oil that they use. Why not use their "secret weapon" in our cars?

    Peteski

  6. #5
    chevelle is offline Cadillac Owners Enthusiast
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    Re: API grades

    Quote Originally Posted by peteski
    Yeah, but trucks usually get very abused and most of them have engines which last for hundreds of thousands of miles without rebuilding.

    That's something to think about... maybe it is the oil that they use. Why not use their "secret weapon" in our cars?

    Peteski
    My brother's Detroit Diesel in his tractor is warrantied on the lower end for 500,000 miles..... It also holds about 12 gallons of oil for the engine. THAT is also how they can run for so long with high mileage oil changes. They carry LOTS of oil in the system...and run huge oil coolers that keep the oil temperature constant regardless of load or ambient. There is a lot more than just the oil...but the diesel oil is definitely very good, no doubt.

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    Re: API grades

    Chevelle, that's a great post. Thanks for the info. I had no idea..... I've heard people say they're using Rotella, but they could never tell me why in a coherent manner.....

    Thanks man.

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    Re: API grades

    Quote Originally Posted by Patrick7997
    Chevelle, that's a great post. Thanks for the info. I had no idea..... I've heard people say they're using Rotella, but they could never tell me why in a coherent manner.....

    Thanks man.
    I also thank you. I always learn something new from your posts.

  9. #8
    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: API grades

    I wonder if it's worthwhile to attempt to find the 10W-30 rotella T oil?

  10. #9
    parts68 is offline Cadillac Owners Fanatic
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    Re: API grades

    I keep a couple of gallon jugs on hand for my John Deere.
    Got it at Walmart

  11. #10
    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: API grades

    Thanks. Picked up some 5W-40 synthetic (blue bottle) rotella. $15 for a gallon. That 10W30 must be impossible to find..

  12. #11
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    Re: API grades

    I put Delvac 15W40 in the ETC, as Chevelle suggested.... $8 a gallon at Wally World....

    Running real smooth... at a stoplight, I'm not sure if it's running or not, it's settled down so much.....

    And yeah, Chevelle, I see what you mean about some of the "extended interval" oils.... they DON'T say "energy conserving II" on them, or have the "For gasoline engines" starburst on the front.... never noticed that before....

    Geez, if I get any smarter, I'm gonna be dangerous....

  13. #12
    chevelle is offline Cadillac Owners Enthusiast
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    Re: API grades

    Quote Originally Posted by Patrick7997
    I put Delvac 15W40 in the ETC, as Chevelle suggested.... $8 a gallon at Wally World....

    Running real smooth... at a stoplight, I'm not sure if it's running or not, it's settled down so much.....

    And yeah, Chevelle, I see what you mean about some of the "extended interval" oils.... they DON'T say "energy conserving II" on them, or have the "For gasoline engines" starburst on the front.... never noticed that before....

    Geez, if I get any smarter, I'm gonna be dangerous....

    Carefull.....standing there in the oil aisle in Walmart and reading all the labels wil cause people to look at you real funny....as probably cause them to start asking which oil they should use.... LOL LOL

  14. #13
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    Re: API grades

    Quote Originally Posted by Patrick7997
    I put Delvac 15W40 in the ETC, as Chevelle suggested.... $8 a gallon at Wally World....

    Running real smooth... at a stoplight, I'm not sure if it's running or not, it's settled down so much.....

    And yeah, Chevelle, I see what you mean about some of the "extended interval" oils.... they DON'T say "energy conserving II" on them, or have the "For gasoline engines" starburst on the front.... never noticed that before....

    Geez, if I get any smarter, I'm gonna be dangerous....
    I am going to look for the elusive Rotella 10W30. I guess the 15W40 is okay to use on a 98 L37, but is there a fuel economy hit?

  15. #14
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    Re: API grades

    Quote Originally Posted by mtflight
    I am going to look for the elusive Rotella 10W30. I guess the 15W40 is okay to use on a 98 L37, but is there a fuel economy hit?
    If there is, I doubt it would be enough to notice without some sofisticated instrumentaion.

  16. #15
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    Re: API grades

    I'm getting identical mileage with the Delvac 15w40..... I was formerly using Mobil One 10w30....

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