There is no need to use additives when a good synethetic, indeed even a good fossil, oil is used. All oil manufacturers that I'm aware of recommend against the use of additives under normal conditions--Royal Purple, Mobil 1, and Castrol for sure. Extraordinary circumstances would be to quickly remove sludge in an older engine with a history of fossil-oil use, for example.

As for change intervals, Road & Track magazine addressed this issue a few years ago in their Technical Correspondence column. They recommend 3k change intervals for fossil oil and 10-15k+ for synthetics. I lab-tested my synethic at 5k and 10k, and at both junctures checked out fine with TBN, viscosity, and contamination at acceptable levels--so I've settled on 10k. I plan on keeping my car indefinitely and don't feel that changing more often will alter the longevity of the engine.

The reason for changing fossil oil more often is that they will oxidize more quickly than synthetics, even with modern additives, and if not changed regularly will form sludge and varnish. In fact, this will occur anyway with fossil products, but earlier change intervals will keep it to a minimum.

As for referrences to STP, this product is nothing but a visocity improver. I saw some tests 20-or-so years ago and adding STP to oil increased viscosity 20 points. Thus a 10w30 would miraculously become a 30w50. This methodology is not only unwise, except maybe in extremely worn engines as a temporary fix for oil consumption, but more expensive than simply using a higher-viscosity oil to begin with. Oil chemistry is a science, and adding additives of any kind may upset the delicate balance of additives already in the oil.


posted by 68.11.185...

• Confirming delco PF53 oil filter is equal to Saab orig, Ron, Fri, 19 Apr 2002 15:25:32
  • Oil filters, Bob Davis, Sat, 20 Apr 2002 12:12:43
    • Have been using extra-large filter that fit. Any harm ?, Hatch_929KAT, Sat, 20 Apr 2002 13:15:30
      • Extra-large filters?, Bob Davis, Sat, 20 Apr 2002 14:13:02
      • Extra-large filters?, Bob Davis, Sat, 20 Apr 2002 14:08:09
      • Extra-large filters?, Bob Davis, Sat, 20 Apr 2002 14:08:09
  • Does it matter what brand oil filter is used?, Joe98, Fri, 19 Apr 2002 16:19:38
    • Well, yes and no, Dick in Falls Church, Sat, 20 Apr 2002 11:09:32
    • Synthetic oil and additives, BillJ, Fri, 19 Apr 2002 17:12:28
      • Re: Synthetic oil and additives, Bob Davis, Sat, 20 Apr 2002 12:03:02 <-- Viewing This Message
        • Still don't understand the 3K mile interval..., BillJ, Sat, 20 Apr 2002 15:11:25
          • Junk oil, Bob Davis, Sat, 20 Apr 2002 23:32:15
            • Not a stupid question at all..., BillJ, Sun, 21 Apr 2002 08:08:20
          • Re: Still don't understand the 3K mile interval..., Dick in Falls Church, Sat, 20 Apr 2002 20:37:25
      • Re: Synthetic oil and additives, Dick in Falls Church, Sat, 20 Apr 2002 11:03:40
      • Oil-guzzling Myths!, BillR, Fri, 19 Apr 2002 18:40:33
    • Yes, it does, Ari , Fri, 19 Apr 2002 16:42:16
    • Re: Does it matter what brand oil filter is used?, 97SAAB, Fri, 19 Apr 2002 16:32:15
  • Re: Confirming delco PF53 oil filter is equal to Saab orig, 97SAAB, Fri, 19 Apr 2002 15:31:15
    • Confirming delco PF53 oil filter is equal to Saab orig, Ron, Fri, 19 Apr 2002 15:50:30
      • Re: Confirming delco PF53 oil filter is equal to Saab orig, 97SAAB, Fri, 19 Apr 2002 16:25:04

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