Originally posted by DemonSVT:
Higher oil pressure DOES NOT mean better oil flow, volume or protection.

In this case it just means more resistance to being able to flow. Which is a bad thing!
Especially at startup and high rpms. Those are 2 areas I definitely would not want degraded oiling ability and protection.


Then top it off with the extra parasitic drag of running the nearly twice as thick oil!!!



I agree. The engine was designed to operate with a 5W-30 oil. That means that the oil galleries that provide a flow path for the pressurized oil to get to all the places it needs to be, the oiling holes in the bearings and the oil cleanances of the bearings are all designed with respect to the flow rates and characteristicts of a 5W-30 oil not 15W-50.

Traditionally it has been accepted that a thicker oil provides a stronger film. Well that is usually true, but a thicker oil needs to have a thicker film than a thinner oil in order to offer its higher film strength. The engine's oil cleanances within the bearings are as such to provide a maximum film strength from a thin oil and the clearances may be insufficent to reap the full benifits of the higher film strength ofered by the thicker oil.

making that extra oil pressure takes power which robs the engine of power that could otherwise be used to turn the crankshaft. The thicker oil also has a higher flow friction, in other words a shaft supoported in a bearing lubricated by a thick oil will be harder to turn than the same shaft and bearing lubricated by a thin oil.

I'd like to see someone test this theory by taking their car to a dyno: With the engine fully warmed up do a run with the 15W-50 oil. Then change the oil to a 5W-30 oil, warm the engine up again to get the oil up to temperature and do another dyno run. I am confident that there will be a definate increase in horsepower with the 5W-30 oil over the 15W-50.

I feel sorry for the people who don't drink. When they wake up in the morning, thats the best they're going to feel all day - former President Lyndon B. Johnson