1996 NA 850 Manual says 10W-30 Why Not 5W-40?

[sleddriver]

I am running Mobil 1 synthetic 15W50 oil.
Car has 180K miles, and oil consumption is as follows:
- 5W30 synthetic: 1 qt/700 miles or so.
- 15W50 synthetic: 1 qt/1500 miles or so.

That's rather high oil consumption on a 50wt. as it amounts to roughly 4 qrts/6000 mi.! Valve stem seals leaking, compression issues or sticking oil rings? Something's amiss....

My engine is far less, with even more miles. And I run M1 10w-30HM for 10,000mi before dumping it.

[sleddriver]

You're right and the truth is that anything xx-30 is too thin for these engines except for those who live in extreme cold climate areas,excluding 10w-30 viscosity.Excluding...because of 10w index.
0w-40,5w-40,5w-50,10w-40 are the most propriate for all year round use,for most climate areas...even in extreme cold ones,excluding 10w-40 which is for moderate climate area because of 10w index.

15w-40,15w-50 & 10w-60 could be used in moderate climate areas all year round.For summer temperatures and for hot climate areas...they are perfect.

I disagree that xx-30 is too thin. First, my owners manual recommends 10w-30. 100% syn. being recommended as well. 10w-40 can be used in significant heat, towing, high rpm operation, etc. but not suggested for "normal driving". Some 30 oils are heavier than others. Oil that's too thick causes high oil pressure and reduced flow, Since oil also carries away heat and t-cars have oil coolers, oil flow is appropriate for cooling as well as lubrication.

I think you'd be interested in the links I posted earlier for PeteB.

[PeteB]

Interesting to see what people are actually using:
https://www.matthewsvolvosite.com/forums ... =1&t=78497

[oragex]

You're right and the truth is that anything xx-30 is too thin for these engines except for those who live in extreme cold climate areas,excluding 10w-30 viscosity.Excluding...because of 10w index.
0w-40,5w-40,5w-50,10w-40 are the most propriate for all year round use,for most climate areas...even in extreme cold ones,excluding 10w-40 which is for moderate climate area because of 10w index.

15w-40,15w-50 & 10w-60 could be used in moderate climate areas all year round.For summer temperatures and for hot climate areas...they are perfect.

I disagree that xx-30 is too thin. First, my owners manual recommends 10w-30. 100% syn. being recommended as well. 10w-40 can be used in significant heat, towing, high rpm operation, etc. but not suggested for "normal driving". Some 30 oils are heavier than others. Oil that's too thick causes high oil pressure and reduced flow, Since oil also carries away heat and t-cars have oil coolers, oil flow is appropriate for cooling as well as lubrication.

I think you'd be interested in the links I posted earlier for PeteB.

W30 is the norm in industry and the W30 grade is plenty enough for engines unless there is a really hot climate such as in places Australia for example. Engines with W30 grade will go well past 300000 miles if the car is mostly driven for long distances on the road. Where the X30 might not be up to the task is on engines that are regularly pushed near the redline or weekend raced. A W40 is a better option for these.
However I tend to disagree about a W40 not being adequate in regular driving. I may be wrong, it's rather an opinion that something scientifically proved.

Just never put a W20 in an old engine