Wide grade specs - what does it mean?

[Silver]

So there are vehicles that may for example spec something between a 20 and a 50 depending on driving habits, mostly high performance cars. I have trouble considering how the internal clearances of an engine can allow for such variance in oil thickness. Not only clearances but timing systems, solenoids, etc.

Are these engines specifically designed for that, or are we putting too much value on the specified grade? What differences might there be in an engine with such a wide range versus one with say a 20 to 30 grade at most?

 

[celicaxx]

I think it's just climatic.

My 94 Jetta and 94 Sentra both had charts going from 5w30 to 20w50 in the manual and under the hood. The Jetta according to the prior owner would throw an oil light on long trips with 5w30, but I never had a problem with 15w40 or 5w40. I ran 5w30, 10w40, and 15w40 in my Sentra with no issues, but in the Philippines it was common to run 20w50 in those cars as it gets really hot and they're idling in heavy city traffic.

 

[OVERKILL]

So there are vehicles that may for example spec something between a 20 and a 50 depending on driving habits, mostly high performance cars. I have trouble considering how the internal clearances of an engine can allow for such variance in oil thickness. Not only clearances but timing systems, solenoids, etc.

Are these engines specifically designed for that, or are we putting too much value on the specified grade? What differences might there be in an engine with such a wide range versus one with say a 20 to 30 grade at most?

Once you understand that viscosity varies massively more with temperature than it does between the grade indicated on the bottle this will make more sense to you.

Engines are necessarily incredibly tolerant of a huge range in viscosity. When an engine is started and it is say -20C, the oil can be THOUSANDS of cP. So the difference between even a 0w-16 and a 20w-50 at operating temperature is nothing compared to that cold start viscosity.

As long as the oil can be pumped (which implies it is appropriate for the anticipated operating conditions) then the engine will be fine.