Originally Posted by SubieRubyRoo
I am with ekpolk on this one... yes, NOACK is a data point, and likely valid in it's own world. But let's think about this: NOACK is a test designed to keep a open cup sample of oil at 250* CELSIUS (482*F) for a full HOUR. There is literally no way to duplicate this outside of a racetrack in the US on any vehicle I know of. In addition to this unlikelihood, we know that there are other bad things that start to happen to an oil in an actual engine when the oil temperature exceeds 300*F even for shorter periods which would likely have more catastrophic consequences long before the oil "boiled off" due to NOACK. So, while an oil may indeed lose 32% of its weight when held at 482*F for an hour in an open cup with constant airflow over it, we do not (at least to my knowledge) actually have a valid way to correlate those conditions to that of a "real-world" engine with oil temps less than 200*F and in a nearly closed-loop system (other than the somewhat small PCV flow thru the crankcase).
The Noack test is to give a relative oil volatility rating. That volatility occurs the most around the ring pack on the pistons and on the cylinder walls because of the extreme combustion temperature. So on a relative scale, an oil that has a Noack of 20% is likely to "burn off" 10% more mass compared to an oil with Noack of 10% under the same temperature exposure in those hot areas of the engine. Also, a V8 will most likely vaporize more oil per mile than a in-line 4 cylinder because there is more exposure to these hot areas ... but a V8 usually has more sump capacity so it all kind of evens out.
I am with ekpolk on this one... yes, NOACK is a data point, and likely valid in it's own world. But let's think about this: NOACK is a test designed to keep a open cup sample of oil at 250* CELSIUS (482*F) for a full HOUR. There is literally no way to duplicate this outside of a racetrack in the US on any vehicle I know of. In addition to this unlikelihood, we know that there are other bad things that start to happen to an oil in an actual engine when the oil temperature exceeds 300*F even for shorter periods which would likely have more catastrophic consequences long before the oil "boiled off" due to NOACK. So, while an oil may indeed lose 32% of its weight when held at 482*F for an hour in an open cup with constant airflow over it, we do not (at least to my knowledge) actually have a valid way to correlate those conditions to that of a "real-world" engine with oil temps less than 200*F and in a nearly closed-loop system (other than the somewhat small PCV flow thru the crankcase).
The Noack test is to give a relative oil volatility rating. That volatility occurs the most around the ring pack on the pistons and on the cylinder walls because of the extreme combustion temperature. So on a relative scale, an oil that has a Noack of 20% is likely to "burn off" 10% more mass compared to an oil with Noack of 10% under the same temperature exposure in those hot areas of the engine. Also, a V8 will most likely vaporize more oil per mile than a in-line 4 cylinder because there is more exposure to these hot areas ... but a V8 usually has more sump capacity so it all kind of evens out.