Understanding why different viscosities are recommended?

[PimTac]

Let us know when you reach 2 million miles on that oil. I'm sure that will be the most historical thread on BITOG.

Maybe even the most hysterical thread as well.

 

[BigShug681]

Originally Posted by PimTac
Let us know when you reach 2 million miles on that oil. I'm sure that will be the most historical thread on BITOG.

Maybe even the most hysterical thread as well.

That's a big if

 

[ZeeOSix]

Originally Posted by chims
Originally Posted by jrh
Something I've always wondered was why do manufacturers recommend different high temp (say 5w30 or 5w40) weights for their vehicles.


W represents winter and not weight. The number after the ‘w' represents the thickness of the oil in normal or warmer temperatures.


Like at 100 deg C "warm temperatures" ... that's some [censored] hot weather.

 

[jrh]

Originally Posted by kschachn
Well that answers my questions about shear stability since it is a monograde oil (with multi-vis properties due to the base stock). There's nothing to shear.

Any observed viscosity deviation would be due to dilution.


Hey Kschachn,
Can you explain or reword your thoughts? Call me simple minded but I don't quite get what you are saying but it sounds important

 

[y_p_w]

Originally Posted by jrh
Originally Posted by kschachn
Well that answers my questions about shear stability since it is a monograde oil (with multi-vis properties due to the base stock). There's nothing to shear.

Any observed viscosity deviation would be due to dilution.


Hey Kschachn,
Can you explain or reword your thoughts? Call me simple minded but I don't quite get what you are saying but it sounds important

A "monograde" is an oil that has no viscosity index improver. He's saying that the viscosity shouldn't go down from use. But unburnt fuel mixing with the oil might.

 

[yowps3]

Originally Posted by Patman
The operating temperature of an engine does change with climate though, at least in terms of oil temperature. On cars that I have had with oil temperature gauges you can see a significant difference in the average operating temperature on the coldest day of winter vs the hottest summer day.

It shouldn't make that much of a difference as long as the cooling system is working.

Of course many of the recommendations for higher temperatures and/or towing assume that the cooling system may not be able to keep up with the oil temps.

Heat Soak & saturation
Cooling systems have a much harder time getting rid of the heat the higher the outside ambient temps are.

 

[ZeeOSix]

Heat Soak & saturation
Cooling systems have a much harder time getting rid of the heat the higher the outside ambient temps are.

Here's a recent thread that shows that effect. Oil temperatures run hotter in hotter weather, even on water cooled engines with a coolant-to-oil heat exhanger.

Oil temps w/r to ambient temps - plotted for my VW Golf Sportwagen

I look at my oil temps all the time in my VW Sportwagen and finally plotted them up to see what is showed. These data were collected on the same route (and after enough time that they stabilized) - a 45 mile highway drive so speed and driving style are consistent with ambient being the primary...

bobistheoilguy.com