Using it in Alusil is going to be catastrophic.
One of Alusil's benefits is that it is actually porous at a microscopic level. This offers TWO benefits: more oil makes its way onto the cylinder walls and the cylinder walls have more surface area to cool themselves.
We want oil on the cylinder walls to prevent wear, of course. We need to maintain a sufficient quantity of oil to prevent the piston rings or the pistons themselves from actually coming in contact with the walls. The pistons are supposed to move up-and-down, not side-to-side...but it happens anyways. If we don't have enough oil to maintain what is known as a hydrodynamic wedge, the pistons will touch the cylinder walls. By having some "extra" oil on the cylinder walls, we have a bigger safety margin.
At startup, oil hasn't made it into every last crevice. This is only for a brief instant, but even at idle we have pistons moving at a very high speed and there is substantial wear. But since the Alusil is already holding some oil in its pores, we can prevent some of this wear.
The other benefit to this added surface area is that the cylinder walls can bleed off heat more effectively. Needless to say, the cylinders are quite toasty. Since we can get more oil in there, we can carry the heat away more quickly as well. Like I've talked about before, oil does more than lubricate; even in a modern engine it handles cooling. If we can keep cylinder temperatures down, we can maintain power output.
Furthermore, If the temperatures are not kept in check, we also experience more wear. The high temperatures will break down the oil and cause thinning. That 5w40, with enough heat, will fall "out of grade". When it falls out of grade, the effective film strength is temporarily reduced and the pistons could scuff the cylinders. There are anti-scuffing additives in oil to prevent this, but at a certain point the explosive power of the piston is going to win.
Audi requires good synthetic oils with sufficient HTHS to maintain film strength. Alusil helps us take full advantage of this. When selecting an oil, we can take further advantage of Alusil's porous nature by opting for oils containing esters. Esters are polar and effectively "stick" to metal. If we can encourage the oil to fill in those pores, that's all the better.
That being said, imagine what happens when you suddenly fill in those pores with metal. Temperatures go up. Less oil gets onto the walls. Neither of those things improve longevity.
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Originally Posted by dparm
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