Its the advanced machining available that allows the very thin synthetic oils - after all, no running in - to be used today, but for the old clunker engines you can guarantee that mechanical noise would be much more noticable!
Consider the oil change intervals too....on many petrol engines, the oil comes out almost as clean as it went in.
On diesels, turbo speeds dictate very high spec oils, and its the detergent within that makes the oil so black.
We notice that there's little distinction between diesel and petrol lubricants these days - often enough, one brew is fine for both.
John
Hang on, did you just say "advanced machining" in a post about 40 year old aircooled VW engines?!
Surely the straight 30 is THINNER (when up to temperature) than (say) a 10W40 (or 20W50, or whatever), with a higher second number? This is the bit I can't understand. I always thought that the advantage of a multigrade was that it retained its viscosity better at higher temperatures whilst not being as thick when cold? So in other words, a straight 30 has a viscosity of "x" at 10 degrees and a viscosity of "y" at 100 degrees (where "y" is a lot less than "x", and a straight 50 oil has a greater viscosity than the 30 at both 10 degrees and 100 degrees, but a 30W50 has the viscosity of the 30 when cold and the 50 when hot. If that's the case, won't the 30W50 will be thicker than the 30 when hot, and about the same as the 30 when cold?
Obviously, I agree that modern machining tolerances are much tighter and bearing materials better, but I think modern cars use the thinner oils mainly to improve emissions and fuel consumption when cold.
Now whether there's OTHER stuff in the modern oils that's bad for older engines is a different question. I believe a lot of the latest advances in oils are to do with making them better for use with cats and particulate filters, but I honestly don't know for certain.
I've run Alfas for a while now and I know that they "like a drop of oil". That's something of an understatement, if they burned any more they'd be 2-strokes!!! Anyway, Alfa have started recommending 10W60 fully synthetic in some of their engines, and I must admit, it DOES reduce oil consumption quite dramatically. I think the huge range of viscosities has only become possible with fully synthetic oils, so for all I know, they'd have recommended it for their older engines if it had been available at the time. I run an old V6 (1989) which does about 750 miles to the pint of mineral 10W40. I've been wondering about trying this tricky new stuff in it (but it holds 7.5 litres so it would cost more than the car is worth)!
