15w50

Hi there,

I'll step in on this one.

I use 20W50 Castrol in my SEC & other 'Summer' cars.

The SEC has had that oil used in it pretty much all its life (92K miles). Another older friend has had nothing but 20W50 Castrol for the last 20 years....

Generally speaking, (and I'm no chemist or engineer) the wider the viscosity range, the higher percentage of polymers added to the oil. We were taught (Volvo Service School) that the polymers weren't all that good at actual lubricating and that a lower viscosity range was better for engine longevity. At the time, the Volvo engineers were sure that these 'additional' polymers were instrumental in unexpected 'premature' turbocharger wear among other things.

Maybe things have changed since those thrilling days of Volvo Service in the 1990s, but I'm stickin' with the Castrol..

In your question, you didn't specify advantages/disadvantages over what, so I stepped up with some personal experiences... which I hope are useful to you.

Cheers, MBL

As Bruce points out, in 10W40 for example, the oil has the same viscosity COLD as 10W (COLD) and when at operating temperature (HOT) it has the same viscosity as HOT 40W oil. Which is to say... pretty stable overall.

Here's the oil viscosity chart for our cars from the Owner Handbook.

Obviously, oil choices were somewhat 'limited' when compared to todays offerings.

Confused yet?? []

Cheers, MBL