Originally Posted By: A_Harman
1. Who said anything about valvetrain wear? You seem to be trying hard to miss my point.
Oh, I don't think that's the case at all
Those who make it a point to focus on ZDDP usually follow it up by claiming that this somehow makes the oil "inferior" to its heavily ZDDP-laden brethren. Otherwise, what is the point in mentioning it if it doesn't matter?
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Ford's reason to formulate the oil with low Phosphorous would be to protect the cats.
So the European marques, who, as you know, also use cats, but in many cases, where the engines aren't roller (like my M5) spec an oil that has higher levels of ZDDP don't care about the cats?
It couldn't just be that the roller OHC engine simply doesn't require the elevated levels of ZDDP that you guys like to see "on paper" could it
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They are probably getting wear protection from Moly and Boron compounds. And besides, valvetrains are designed to run at the same contact stress limits whether they are OHC or OHV.
A roller motor doesn't have a sliding contact patch with respect to the cam lobe/rocker/lifter interface. This is relevant.
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2. Yes, we know from the SVT data that the GT500 engine shears MC 5w50 an average of 32%.
But we don't have any HTHS data on the oil post-sheer, correct? (I can't check that UAO thread right now because their board is down).
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But we also see from the same database that AMSoil 10w40 only shears about 6% in the same engine.
But this means what exactly in the context of this engine? Other than the obvious, without tear-down testing, or being privy to Ford's testing protocol for the spec cited in the owners manual, it means that in this application, this oil shears less. Nothing more, nothing less. It doesn't mean it is a desired trait for the application or that it is beneficial, now does it?
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So you can't say that the "same effects apply to a lighter oil". It's the viscosity spread that drives high levels of shear loss.
Really? So Mobil 1 0w-40 SM and Mobil 1 0w-40 SN, the former shearing far more readily than the latter must be a figment of my, and the board in general's imagination? Got it.
There have been numerous incredibly sheer-happy 5w30's posted in the UAO section in the past. And that's a far narrower visc spread than either oils we are discussing here, is it not? It couldn't just be that the propensity to shear relies on a multitude of factors including application, base oils used, visc spread, polymer content...etc.
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In general, a 10w40 will shear less than a 5w50. Likewise with a 5w40. I have 36,000 miles of experience with RT6 5w40 in my truck, and know that it doesn't shear. (Not that I would recommend it for the Boss.)
Using the context of "in general", as noted, I will agree with you. However, of note, run a 5w-40 in a 6.0L PSD and see how long it takes to shear the living poo out of it. Spoiler: not long. That same oil in a 500HP detroit doesn't shear at all though
Or in a 5.4L modular. Application is a key component to whether you will observe shear. Yet in many cases a lubricant that does shear is an approved product that has been tested by the manufacturer, so this is, from what we can glean from this, an acceptable characteristic. And I would bet that this is likely due to the oil, post-sheer, still having an acceptable HTHS for the application, subsequently meaning that its desired operating characteristics have not been compromised, regardless of the observed viscosity loss.
But all of this is beside the point, which is the fact that Ford has required the use of a lubricant carrying a specific approval and to comply with the terms of his warranty, that is what the OP should be using.
If he wants to use City Star 5w30 with 4 cans of MMO after his warranty is up, that'll be on him. But while operating the car under warranty, he would be ill-advised to use a non-warranty-compliant product for this application. It really IS that simple.