Originally posted by speedybenz
Some of you guys need to get with the times. High performance engine builders and race engineers all use 30wt or lower viscosity oils. Not to save money, but to win races and races can only be won if you finish.
So they are not going to risk there multi-million dollar budgets on a few bucks of oil. But these low viscosity oils due protect engine bearings and parts and due allow for decreased friction and more Hp.
So if Mercedes wants to spec 40wt oil great you old timers stick to it, spend more money on gas and feel good, but you are not doing any good for your engine, except maybe harm as the high viscosity oils take minutes to warm up and your engine parts are rubbing and creating high temps and increased wear.
Firstly, they also completely tear down and rebuild those engines after each and every race, sometimes after every couple of laps during qualification, and they go what, 500 miles in a race? (except the LaMons of course)
Higher viscosity oils will actually take the load in a journal bearing FASTER than a lower viscosity oil, and thus reduce the metal to metal contact time. In a journal bearing, such as cam bearings and mains, it is only the oil that takes the load, and there is no metal to metal contact anywhere....follow so far? The reason for this is due to the relative velocity between the two surfaces, bearing journal and bearing, and the viscosity (or resistance to shear loads) creating a normal force due to a pressure differential. Believe it or not, the very thin, microscopic layer of oil directly in contact with each surface, journal and bearing, has zero relative velocity to that surface, in other words, it is 'sticking' to that surface, so lets say the bearing is rotating at 900 rpm, the microscopic layer of oil in contact with the bearing is also moving at that 900 rpm rate, and the oil in contact with the journal has zero velocity. The relative velocity differential across the layer of oil (from 0 to 900 rpm, in a nearly linear rate), creates pressure that focuses inward away from the journal, which keeps the bearing centered within that journal always. The bearing diameter is ALWAYS smaller than the journal inner diameter right? That difference is called clearance.
That clearance is a "highly engineered" value, (read a couple of calcs performed to find an optimum value based on several inputs, mostly of fluid drag vs. wear) True, higher viscosity oils have more friction, but this friction is in the form of fluid drag, like the difference between swimming in water vs. molasses. So, you want the highest performance, use an air bearing. Pretty easy to design, and filtered air is always readily available and has an order of magnitude less drag right? The problem is starts and stops when the bearing surfaces contact.
Yes, you can design motor journal bearings with tighter clearances to use lower viscosity oils for less friction loss and thus some improved economy. The problem is that you sacrifice bearing life to do so. Through in some contamination and you really have decreased reliability.
The bearing clearances on the M103 engine in my 300E were not engineered for the 0W-40 type ultra low viscosity oils. I'll stick with the MB recommended viscosity oils for the temperature range I'm expecting to drive in, which right now is 30F to 85F, so I'm going to use some 10W-40 for my next oil change coming up in 500 miles. If you want to run your motor with these ultra low viscosity oils, be my guest, but I'd like to see your calculations first
(I did DOZENS of these bearing calcs in my machine design and dynamics of machinery classes in college). Personally, I'd rather stick with the MB recommendations and get 300K + miles out of my engine. (Am I setting my standard too low? 500K?)
Mineral oil vs. Synthetic....hmm, normally I wouldn't touch this with a 20' pole due to the political ramifications
However....the two largest contributors to enginer wear are viscosity breakdown effects at cold starts (oil viscosity broken down, lower viscosity, therefore longer time of metal to metal contact during initial startup), and from contamination. Bulk contamination is trapped by the oil filter, but no filter can capture the other contamination, chemical. Combustion gases in the crankcase mix in the oil and create carbonic acids which eventually etch the metal surfaces...no oil, mineral or synthetic are immune to this, although some oil additives in both types are better at bufferring these acids. My personal choice is to use mineral oil and change it more often. The cost to benifit ratio doesn't play out with the double cost of synthetic for this reason.
HOWEVER...on my motorcycle (Kawasaki GPZ1100 with 11:1 compression and 120 HP, very fast) I have noticed a large improvement in shifting when using synthetic. Bear in mind that on most motorcycles the engine and transmission share the same oil. Motorcycle engines for this reason break down oil viscosities quicker than car engines do, and the synthetics definately hold up better....I still haven't bought into the motorcycle specific synthetic arguement though. (the claim being that car formulated oils contain friction modifiers that can contaminate wet clutch disks and cause clutch slippage....I haven't noticed any clutch slippage and tend to think that those riders who do probably either had a marginal clutch to begin with or are the type to fry their clutch trying to ride wheelies...
BTW, my background? Mechanical engineer working at a nuclear power plant who's ridden motorcyles for 20 years now, and has been turning wrenches for about 25 years. Whew, long post.