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oil change and starting
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TR6oldtimer
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/bcforum/images/%%GRAEMLIN_URL%%/nonod.gifBrosky said:
Sorry Paul, but actually a 20w-50 engine oil will increase it's viscosity as it heats up. Over time the additive that causes viscosity to increase with temperature will break down and the oil's viscosity at temperature will begin to decrease.
TR6oldtimer said:
Umm not quite. oil viscosity indexes are related to oil temperature. For a single wt oil it is intuitive that the oil will be thinner as it heats up.
For a multi wt oil, at low temperatures, it will approximately as the lower viscosity # but as it heats us it will act like the higher viscosity# however since viscosity of oil is affected by temperature, the actual viscosity of the oil will be lower at the high temperature, it just won't loose quite as much viscosity as a single wt oil would have.
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I agree.70herald said:
See the attached chart.
An SAE 20 oil at 100F will have a viscosity of about 350 SUS. At 210F it will be around 55 SUS.
A SAE 50 oil at 100F will have a viscosity of about 1050 SUS. At 210F it will be around 92 SUS.
A SAE 20-50 oil at 100F will have a viscosity of about 350 SUS. At 210F it will be around 92 SUS.
Note that gear oils are rated differently. A SAE 90 gear oil is actually quite close in viscosity to a SAE 50 engine oil.
D
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TR6oldtimer
Darth Vader
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'I are a rock sometimes'.
Of course oils become less viscus when heated. What I really ment to say is that over time motor oils lose their ability to maintain rated viscosity. So in our cars old oil would be less viscous at operating temperature then new. (However, some oils will actually go the other way and increase in viscosity due to sludging.)
As to whether one would notice a change in performance after an oil change I guess would depend on how old the oil was, or more likely it is just the feel good thing of doing it.
Of course oils become less viscus when heated. What I really ment to say is that over time motor oils lose their ability to maintain rated viscosity. So in our cars old oil would be less viscous at operating temperature then new. (However, some oils will actually go the other way and increase in viscosity due to sludging.)
As to whether one would notice a change in performance after an oil change I guess would depend on how old the oil was, or more likely it is just the feel good thing of doing it.
Brosky
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I just wanted to stir up a discussion and it looks like I was successful. Thanks, I did learn somethings about the heat / viscosity factors that I did not know.
Besides, everyone knows that to raise compression over one point you would have to not only wash, but wax the car as well. This after an oil change, of course!
Besides, everyone knows that to raise compression over one point you would have to not only wash, but wax the car as well. This after an oil change, of course!