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Some folks will have guessed correctly what I am posting.

"
I also own an '86 900 8V base model (bought new) and have put nothing but Castrol 10w 30 in it. It still performs like a gem...
"

Older cars has less specific HP, and the piston rings were lower from the top of the piston... away from the heat. Oil does not circulate around the compression rings. So whats there can cook, changes or not. With the modern designs, the top ring is much closer to the top of the piston* and the oil formulations have been largely driven to avoid coking the oil in the ring grooves. That does not mean that it is not going to occur, only that the oil formulation in a test engine under certain conditions will not exceed a certain deposit condition. The hot spot in engines is the top ring, the turbo bearings are not the critical area now. The rings can coke in NA engines too, and many have higher compression ratios than the turbo charged engines. So the heat may be higher under the grind of cruising conditions than a turbo engine. Synthetic oils were first developed (the true synthetics, not FakeTec(tm)), to resist the heat in the turbine bearings in jet engines. There is a similar need for this heat resistance in the ring grooves.

* The rings were moved up higher to reduce emissions and increase combustion efficiency. AF mixture forced into the piston clearance gap above the rings does not get fully combusted. So the change was made to reduce that gap volume.

posted by 68.95.73...

• Another oil question!, Patrick, Tue, 6 Apr 2004 18:41:35
  • Believe it or not!, Patrick, Wed, 7 Apr 2004 16:09:24
    • t'was before the premier of The Sludge that Ate Saab, :-), Wed, 7 Apr 2004 16:38:53
      • Re: t'was before the premier of The Sludge that Ate Saab, Patrick, Thu, 8 Apr 2004 04:16:18
        • Stephen's right, this info was replaced in July '00, Eiron, Fri, 9 Apr 2004 14:17:52
    • Obsolete Recommendation, Stephen Goldberger, Wed, 7 Apr 2004 16:38:32
  • oil suspension of sludge, Craig S, Wed, 7 Apr 2004 11:26:28
  • Re: Another oil question!, Dean, Tue, 6 Apr 2004 22:06:35 <-- Viewing This Message
  • An oil answer--, Dick in Falls Church, Tue, 6 Apr 2004 21:21:19
  • It's the viscosity, Stephen Goldberger, Tue, 6 Apr 2004 21:10:57
    • Re: It's the viscosity, but what if...?, Patrick, Wed, 7 Apr 2004 07:22:02
      • use what is recommended in the owner's manual, compaqted, Thu, 8 Apr 2004 09:43:30
        • Re: use what is recommended in the owner's manual, Eiron, Fri, 9 Apr 2004 14:07:12
      • Re: It's the viscosity, but what if...?, Dick in Falls Church, Wed, 7 Apr 2004 07:27:45
  • Switch to fully synthetic and change every 5 months., J, Tue, 6 Apr 2004 19:30:46

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