XC70 oil grade

[happy wanderer]

Hi all, I have recently acquired a 2008 reg. XC70 2.4D5 with 122,000 miles on the clock. Should I use a thicker oil than 0/30w recommended when I do the oil change considering the mileage it has covered?

[StanC]

No.

I still use 0W-40 fully-synthetic oil in my 178,000-mile 960 3ltr petrol and I don't need to top-up between changes. If your car has been well maintained, then 122,000 miles on a diesel engine is nothing. Moreover, the thinner oil will give better protection on start-up, when most wear occurs. I would consider moving to a thicker oil only if and when the engine starts burning significant quantities of oil.

Stan

[AndyV7o]

No, 122k is nothng for a D5, theyll do 4x that or more.
0w30 is fine, if you insist on going thicker, that would be 0w40.
You can use 0w30 or 0w40 A3/B4 instead if you wish for better potential protection.
But, again, 0w30 is perfectly fine.

[DaveNP]

Personal experience, but I think thicker oil was what did for my 850, with hydraulic tappets and the need for oil reaching all parts of the engine efficiently putting something thicker in just hampers the proper operation, you'll cause more issues with the bits that did work than 'cure' any possible wear issues. I'd stick with the 0w30.

[AndyV7o]

Originally Posted by DaveNP

Personal experience, but I think thicker oil was what did for my 850, with hydraulic tappets and the need for oil reaching all parts of the engine efficiently putting something thicker in just hampers the proper operation, you'll cause more issues with the bits that did work than 'cure' any possible wear issues. I'd stick with the 0w30.

This is usually people (not commenting on your own reasons DaveNP) getting the wrong end of the stick and, for example, changing 0w30 for 10w40 'cos its better, its thicker so its better' or for example saying '0w30 is way too thin, I use 10w30 cos its an old engine' those kinda things. Its changing the 0w/5w/10w that causes the most trouble. 0 is around 6x thicker at 40° than 30 is at 100° and about 5x thicker than 40 is at 100°. 40° 10 is about 8x thicker than 100° 30 and 7x thicker than 100° 40.
The engine is designed around the oil being hot. So when an engine is designed to run on oil with a viscosity of around 12cst (hot 30) and you put in oil that thickens to around 97cst (40° 10w) instead of around 70cst (40° 0w) at temps exceeding those of our climate in summer, let alone winter, you can get an idea how things are going to get stifled. The pump has to work harder, hydraulic tappets get locked solid, oil reaches places slower...
Changing the latter, hot, number however isnt as much of an issue, if sensible, but can still cause problems. Changing 30 to 40 is going from 12 to 14 cst at 100°. Some people in the 'thicker is better' camp may use 10w60 oil, this is an extremely specialist oil and can actually wreck an engine sooner than protect it.
You also get into hths, which is another very complex story.
A3/B4 are high hths A5/B5 are low hths.
What this means in a (very rudimentary) nutshell is A5/B5 will flow faster/easier for the same viscosity, but has less hydraulic capability in the bearings thus can allow metal-metal much more readily than A3/B4. If we liken it to custard mixed to non-newtonian consistency, you would sink easier in A5/B5 than A3/B4. You could be bigger and slower running across A3/B4 than A5/B5 where you'd need to be light on your feet and quicker. Though the measured static viscosity remains the same, the 'robustness' and pumpability of the oil under pressure differs somewhat. What this means is that you can have a 30 and 40 oil hot, and if they are both the same hths, they are both the same in terms of pumping and 'robustness' in the bearings.
So, dont get hung up on oil myths, stick to what the handbook or an oil specialist tells you.
If it says 0w30, dont go worrying about it 'being too thin' cos you could cause more trouble by going thicker!

[DaveNP]

Originally Posted by AndyV7o

This is usually people (not commenting on your own reasons DaveNP) getting the wrong end of the stick and...

Well lets just say I truly ended up holding the sticky end of the stick
I think it's fair to say oil has changed enormously over my lifetime, more so for those who are older than my 58 years. I can remember as a child that my dad would change the oil in his cars twice a year, spring and autumn, thin oil for the cold winter starts and thick oil for long hot summer drives*. He didn't have the benefit back then of the multigrades that we do now, and I don't suppose the oils were as stable either for longer service intervals. Unfortunately this rudimentary approach to oils still lingers in the subconscious of the motoring world and when my 850 was supposedly showing signs of wear I fell for the 'you need a good thick oil' line. My subsequent learning, some of it from Andy's excellent thread on oils and some from extensive hours reading articles on the web (including having to read further articles on measuring viscosity, polymerisation etc. in order to understand the first articles) means I'm now at least aware that there's a lot more to it than 'thicker is gooder'.
Even as Andy mentions the ACEA and API numbers can be a bit misleading, one might assume that the later the spec the 'better' the oil, but replacing 'old fashioned' A3 with 'newer' A5 could give you problems.

edit*Can you imagine the fun we'd have on the forum if that were still the case? Every spring and autumn there would be the threads on 'Have you changed your oil yet?' and all the heated replies about too soon, too late, I don't need to, it's just a marketing scam etc etc.

[AndyV7o]

Well Im glad you found the thread useful, and once you go down that road of studying oil, what a bloody minefield eh!! To grasp the basics you almost have to do the equivalent of the first year of a tribology degree, and so many intertwined properties and aspects it would make Tarantino sweat!

Yes, if we still had summer & winter changes, the forum would probably melt! (I guess they could use a thicker forum to cope with the heat 😂 )