I respectfully disagree. The rating of thermal breakdown by API is a farce.
Unless an oil loses 15% or more of its weight in a 1 hour period, at a certain temperature, the oil company is able to advertise that thermal breakdown is not occurring at that temperature.
What this means is that if an oil is kept at 300* for one hour and loses 10% of it's weight via vaporization or "volatilization" they can advertise that it has not begun to have thermal breakdown at 300*.
When in fact it began thermal breakdown the minute it starting vaporizing even 1/2 of 1% of its weight.
The reality is that most Synthetics begin vaporizing at around 280*, and most conventionals around 270*.
Since temp readings on our HD's are not taken at the point where the oil is the hottest, the temp reading of 250* is most likely reflecting anywhere between a 270* - 300* temp of the oil at its hottest point in the engine.
Adding to the above, quite apart from vaporization, is the fact that most folks are running a 20W50 oil. 20W50 oil is a straight 20 weight oil that has viscosity modifiers in it. These modifiers make the oil less fluid/more viscous the hotter they get. Problem is that too much heat cripples these viscosity modifiers so they no longer fully function to make the oil more viscous when heated up.
So at 280* the oil is suffering thermal breakdown AND the VM's are no longer as effective at mimicking a heavier weight oil, so when you need it most, you have an effective 25, 30 or 40 weight oil, instead of the 50 or 60 weight oil that your HD manual calls for in warmer ambient temps.
Kevin
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Originally Posted by DK Custom Products
