Originally Posted By: wemay
http://www.amsoil.com/lit/g3115.pdf
TEOST (testing conducted by AMSOIL) is arguably more import to D.I. applications. Link is above.
Really it's a sufficiently high valve temperature and proper PCV design that's critical for valve cleanliness.
But about TEOST, the issue I have with aptly applying TEOST 33C to DI intake valves are the major differences in oxidation modes.
33C cycles between 200°C to 480°C in a non-turbulent environment with only 100cc of oil
laminarly flowing over a heated surface, in the presence of an oxidant catalyst, no-less.
An intake valve must remain above 400°C to resist deposit formation from vapours and mist of the oil that should not even be there in the first place, that has been separated from the bulk by more than one mode.
Atomization - reflecting poor separator design and/or blow-by
and of course volatilization:
Additives like phosphates and any other volatile additives will be of a higher concentration 'in the vapour' than the bulk oil; additive volatility is an issue (independent of oil volatility). Reason 1 why TEOST 33C is not apt.
Then there are the HC chains that have seen sufficiently high local temperatures to change their phase. Not only that, but the new vapours have a significantly higher exposure to oxygen in the crankcase, enabling rapid oxidation of those vapours, so that when they re-condense (on any surface, incl the valves) it does not exactly resemble the fractions that were vapourised in the first place. Under valve-cover varnish?
That's the difference between vacuum distillation/condensation of crudes to make bases and the same process occurring in the crankcase; the oxygen present in the latter. It's lke the fast track to oxidative thickening IMO.
A fantastic solution to this problem is avoiding the volatility in the first place, with the selection of suitable grade and quality
Interestingly enough, 0w20 has no specified TEOST limit.
