Latest from Castrol re flat tappet engines...

Just a few observations then I'm done:

Nomenclature: for whatever reason, when the subject of engine oils is discussed, the industry uses the term "flat tappet" to really mean "finger follower (Porsche SOHC with rocker arm, no roller) and overhead bucket lifter designs, along with high ratio/solid lifter/stiff spring pushrod designs". They know what they are talking about, they just use a term that seems odd / incorrect.

History: SL motor oils had zinc / phosphorous limits of approximately 1000ppm (depending on VI, etc); these were the oils in the market until fall 2004. From 2005 on, conventional road use automotive motor oil has been limited to 800ppm zinc / phosphorous (SM / GL-4). So there's only a few years of real-world experience with these oils.

SM wear tests: the SM wear tests that the GM letter references don't quite cover 50k miles of use. Nor 30k miles. In fact, they cover approximately 3k miles of continuous single-speed operation. If there damage is microscopic but within limit for a 3k mile test, how much damage will there be over the course of 30k miles of real-world driving, even assuming a 3k mile drain interval? Logic says greater than zero, and greater than one test interval's worth, but hey, YMMV and, after all, all engines can tollerate some cam wear....

Friction modifiers: SM oils achieve their results by using higher levels of moly and/or boron friction modifiers in place of the ZDP. These materials have been known for close to a century, but they are more expensive than ZDP and, more importantly, their operational mechanism is different: where ZDP builds a protective coating at the wear interface, moly and boron don't. The consequence of this is earlier depletion of the protective agent.

Drain intervals: can you beat the reduction of ZDP by using a shorter drain interval, say 3k? Possibly, but there's no real world research one way or the other on this, so you're on your own: a one-subject test with no control group.

ZDP requirements: the anti-wear and anti-friction requirements come down to the issue of contact pressure at the cam lobe and time, and of course driving habits. A blown rat motor with high ratio rockers and high lift valves may not survive an hour on a road-going SM oil (even after break-in), but that's an obvious fail. An '81 911SC may go 10-30k miles before showing severe cam wear, or may survive longer or shorter. What's the contact pressure for the 911 app, and what's the contact pressure in our 3x8 motors? I don't know (wish I did), but it's definitely on the high side, much higher than for today's roller hydraulic lifter designs. In fact, the SAE says the rule of thumb for these valve train designs is 1200ppm zinc and phosphorous - but that's just a rule of thumb. Can you cut that value by 30% and get away with it? Maybe, maybe not.

Economics and regulatory pressures: Note that this problem starts with the EPA mandating longer cat life (now mandated as a 150k mile part), putting pressure on the OEMs. The OEMs are pressuring the oil companies (as their biggest clients). Since the subject of selling came up, I will ask: does Castrol want to sell you motor oil? Does GM want to keep your old Ferrari or Corvette on the road? Does GM want to sell you a new cam, long block, or shiny new Corvette? Does GM want to keep the EPA reasonably happy and off their case (read: hefty fines)? Does Castrol want to point their big oily finger at GM and say "they made us do it, they won't let us sell the right product for you"? For that matter, who exactly, other than you (us) wants to keep your old Ferrari / Porsche / Corvette / street rod on the road?

Looking at the matrix of Mobil 1 products posted in this thread (thanks for the current version, I haven't looked at it in a few years!), there are a few products on that chart other than motorcycle oils that would be good / acceptable choices; 1000ppm zinc / phosphorous may well be ok as that was the SL limit and reports of problems only really started surfacing with the introduction of SM in 2005. But then again, the SAE says 1200ppm is generally required for these valve train designs. It's unfortunate that we're left in this spot: amateur enthusiasts shouldn't have to play lube oil engineer! But we're here, so I would suggest it's best to make an informed decision: pick your poision wisely!

-frank

 

One more last thing to add: turns out that several motor oils say "API SM" on them (including my choice, Mobil 1 Racing 4T mc oil), but they have high levels of zinc / phosphorous. (As was pointed out earlier in this thread.) I replied that these oils do not claim GF-4 compliance, and that's the key - which is true, but turns out it's only part of the story.

The non-road-going oils that say "API SM" are claimed by the manufacturers to meet the SM test standards, but the manufacturers are not using an "API SM" licensed additive package for these oils and thus can't display the API "sunburst" logo. These oils don't meet the full standard of SM as they contain too much zinc / phosphorous (SM does indeed limit zinc / phosphorous to 800ppm), though the manufacturers claim the oils meet the SM performance tests.

So the rule becomes simpler: if it's got an API "sunburst" logo on it, with an SM service rating, then it's got 800ppm or less zinc / phosphorous. If it doesn't have a "sunburst" logo, but says "API SM" in plain text on the label, it may (or may not) have higher levels of zinc / phosphorous (you need to check the spec sheet): this is an unlicensed claim of meeting the API SM performance standard. (Seems to me the oil companies are treading a very fine line here with misusing a trademark, but hey, I'm not an IP attorney.)

-frank

 

While there is an excuse it will be used.

Ferrari engines are just engines, they are not that different to many other engines ... we like to think they are but they aren't (sorry).

If ZDDP was really that important there would be millions of engines through out the world self grinding their cams ...
Pete

 

well gents, you can stick with whatever oil mythology you wish.

i'll stick with mine and continue to use brad penn.

 

Actually now that you have said that, their term is correct, because a tappet is really a rocker not a cam follower. Interestingly though a lot of engines (even twin overhead cam ones) do use rockers so that valve adjustment is a simple task. I'm not sure though if they are roller or not ...

Pete