[Vwdiesel] Synth vs Dino Oil...

[Gerry Wolfe]

Call me old-fashioned, but here's my $0.02Cdn...  Rants based on my (perhaps inaccurate?) knowledge...

An oil such as 15w40 is basically 15w oil with a bunch of viscosity improvers to lower breakdown at high temperatures so that the 15w looks like 40w.  You gotta believe that these viscosity improvers get contaminated or used up over time.  Will oil analysis show this?  I personally doubt it.  My guess is that the best choice is to use a combination that has the least variation e.g. 15w40 vs 5w40.

Second rant: My '91 TD calls for a "minimum" level of CD.  Virtually anything on the market today is going to far exceed these standards.  However, the newer oils with their CH and CI standards do a much better job of keeping soot suspended.  I'm again thinking that this has to be one of the most important considerations for a diesel engine.  Will oil analysis show this?  Again, I doubt it.

My approach is now to use a good quality dino 15w40 weight oil and change it regularly (in my case, quarterly or about every 5K km).  When I had the head gasket replaced a while ago (around 275K km) I also had the cylinder head reconditioned and the rings replaced.  There was virtually no sign of cylinder wall wear, not even a ridge at the top of the piston travel.  Even the rebuild mechanic was surprised.

Now, to contradict myself... I always let the engine cool down a bit after a heavy hiway run to let the turbo cool (synth oil is FAR superior to prevent coking) and if I still lived in a really cold climate (like I used to) I would be using 5w40 or even 0w40 in the winter.  However, even the lowly 15w40 is still acceptable down to almost 0F according to Bentley etc.

And, not all dino oils are equal.  Check out the specs on various 15w40 oils, and you will see considerable difference in pour points etc.  I checked out Rotella 15w40 dino, and it's pour point is not really that far away from their 5w40 synth.

Rgds to all, and it's great to see friendly discussion and banter again in the group.  Kudos to our moderator!

GerryWolfe at shaw.ca
www.members.shaw.ca/GerryWolfe

Ninety percent of being smart is knowing what you're dumb at.