does the xW number even matter anymore?

[cryptokid]

for a standard 3k 3month oil change interval, wouldnt it make most sence to run a 0wxx no matter what climate you are in?

the only reason i can think of to use a higher cold number is for an engine which develops sludge quickly. as a 10w30 will not sludge as easily as a 0w30 for example, because the 0w30 has more VII's than the 10w30.

am i correct in assuming these 2 things?

 

[buster]

When and if I run an oil with a 0w, more VI's, I am going to run a maintanence dose of Rx with it. Your right though, the spread is more ideal at a smaller amount like a 10w-30.

 

[Dr. T]

You run a higher cold number because you can eg. you live in Hawaii and it's never below 50F.

As far as the sludge issue...I had much more with a 5-30 than a 5-40. I don't think it's a VI issue as much as it's the oil breaking down because it was too thin to begin with.

 

[cryptokid]

quote:

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You run a higher cold number because you can eg. you live in Hawaii and it's never below 50F.

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although i used to go by that logic, i dont think i will anymore.

 

[Dr. T]

Why not? I live in Toronto and a grade such as a 5-50 would be more appropriate for year-round use compared to say, Hawaii or Australia where one could comfortably use a 20-50 all year because extreme cold is not present in these places.

 

[widman]

I prefer to stay with the higher number for the temperature...... less drain off of parts and less leaking.

 

[WeyounDS9]

quote:

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Originally posted by Dr. T:


As far as the sludge issue...I had much more with a 5-30 than a 5-40. I don't think it's a VI issue as much as it's the oil breaking down because it was too thin to begin with.

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Yes,

Large spread and VII's, tend to result in extra varnish.
Extra sludge comes from running an oil that is either too thin or too low a quality.

Fred...