There are two ratings the 'W' one (as you say, this is for 'winter') and the non-W one, which is for operating temperature. Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing Hence a 5W30 behaves like a 30 weight oil when hot but a 5 weight oil when cold (which is likely still a hell of a lot thicker than hot 30 weight oil - but suspect Weasley can give us some accurate figures for that and I rather hope he does to further my knowledge). But a multigrade can change its viscosity less as the temperature changes. A conventional 30 weight oil would be very thick when it is nobbin cold. The W rating (Winter if I remember correctly) is how viscous the oil is when it is very cold. Hence a 30 weight oil is a certain thickness at a certain temperature. This thickness / viscosity is measured at a particular temperature to give an oil viscosity rating / weight. The reduction in viscosity for a given increase in temperature is less for a multigrade oil than for a straight oilįisty: after polishing the tank with the glistenng beads of sweat from my full hot scrotum, I filled the headrace bearings with 10cc of my manmilk 89 landmarks, 3 months, 9,500 miles.ĥ weight oil is thinner than 30 weight oil, but the change in viscosity over a temperature range is high.Ī 5w30 oil acts at 0C acts like a 5 weight oil at 0c, but like a 30 weight oil at 100c when at 100c I did the 2010 Round Britain Rally on my 350 Bullet. That's when you find out everything you want to know.” “Rule one: Always stick around for one more drink. Both are measured at 100 degrees.ĥW is not an actual measure of viscosity as such, it's what a 5 weight oil is like at -30 degrees and is in fact much thicker than 30 weight? 5 weight is a much thinner viscosity than 30.
I think where I've ben getting confused is that 30 weight is a particular viscosity measured on a scale. I just tried looking this up and many sources seem to be implying the oil gets thinner as it gets colder which is patently not the case. With viscosity numbers, a higher number = thicker/more viscous.
This is something I have clearly misunderstood for a long time.
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