[Vwdiesel] RE:Gunked up case, good parts- Clean case,

[Val Christian]

> I haven't seen a detergent oil since I was a kid.  Do they still sell them 

	I believe that detergents are in engine oils still.  The problem 
	in the old days is that there would be a crudded up engine, and
	someone put in a detergent oil, and voila, there were chunks of
	crud floating around.  Usually something like a lifter would
	suffer a stroke.  Sometimes it was some oil passage.  Bad news.

	Even the straight weight 30 I just put in my pressure washer 
	B&S engine is detergent.  There are some engine oils, which 
	do not have detergent additives.  W aviation oil is one, if 
	I have my stuff straight.  AD aviation oil has a dispersent
	in it, which is a detergent,  The A stands for ashless, which
	is the oil Hagar likes (probably because he has a barn full
	hidden in the north country).

	Since everyone is using some kind of detergent these days, it's
	not a big deal.  The detergent is a wetting agent, which helps 
	keep the crud in suspension.  In a simplistic way, when you 
	change oil, you dump the crud.  

	I seem to recall from a aviation mechanic's refresher course 
	a couple of decades ago, that a quart of oil will hold a pound 
	of dirt at 100F.  Drop to 0F, and the dirt capacity drops to
	about an oz.  Some people change their oil when they shut down
	the engine.  The oil is still hot, the dirt is all sloshed up
	(and presumably in suspension), and you ahve to be ginger so
	that your fingers don't become french fries when you pull the 
	drain plug. This practice is probably good for the engine.
	It takes forever for the dripping to stop.  In the days when
	life was simpler, I'd just drain oil on Friday night, and 
	finish the job Saturday morning.  Now I hope that one of my 
	family doesn't jump into the car while I'm working on it and
	try to drive off.  (It really almost happened once.)


>    The best lube   for one engine here is 30 SAE straight mineral oil.

	The advantage of straight weight, especially in stationary
	powerplants is significant.  They tend to do little start/stop,
	so catering to cold start temps with a multivis oil is significant.
	Second, the viscosity index improveres are not lubricants.  In
	wide range multi-weights, the VI agents can be 30% of the volume.
	So keeping a straight weight in, keeps the most lubricating juice 
	at hand.  Finally, a multivis oil is made with a light base oil.
	Then the VI additives are introduced.  So it behaves like a light
	base oil, and the VI agests help out when temps get higher.
	This means that a multivis oil drains down in an engine faster.
	For most of us this isn't a big deal, but after a day or so, 
	there is a measurable difference between a 10W30 oil and a 
	straight 30 oil.  

	So absent specific needs, I tend to like straight weight oils.
	
	Disclaimer: I'm not a triboligist.

	Val