Oils ain't Oils

The above is a quote from an ad we used to have here.  It was very effective, even a little entertaining for a while, but it was wrong.

Oils is Oils - Synthetics aside,oil is dug up from the ground, base oils are essentially the same no matter who you buy from.  The same fractions are used to produce particular grades.  Some cheap oils are made from recycled oil, but the issue with these is how pure they are, not the quality of the base oil.

Grades is grades - If an oil is specified to have a particular grade, it will be made to meet that specification.  Low quality reclaimed oils aside, the performance of the oil will be pretty much equal across various manufacturers.

Additives is additives - the base oil is the same, and in fact may be the same between a single grade and two different multigrades. The difference is in the additives. The main additive is the viscosity improver, which is what creates a multigrade oil. the base oil will actually be close to the viscosity that the single grade would have at high temperature, but special long-molecule additives cause it to not thin out at these high temperatures and increase it's shear factor, so it behaves the same as a heavy weight oil at this point.
Other additives are anti-oxidant, anti-corrosive and anti-galling (ZDDP.)

Old oils, as were originally specified for VWs, were single grade oils. It was necessary to have an oil heavy enough that it would not thin out too much at operating temperatures, while still pumping well and not gelling at the lowest temperature experienced.  You may remember pouring such oils into engines, they were noticeably viscous, a bit like warm honey, while modern oils pour a bit more like water.

If the oil became too thin, it could not provide the lubricating barrier needed. VW, like most four stroke engines, use pressure-lubricated flat bearings. The bearing surface itself is quite soft as you may have noticed, it's main purpose being to hold a film of oil.  If the crankshaft is perfectly balanced and the oil pressure sufficient, the crank should be spinning inside a thin film of oil, never actually touching the bearings. Of course, we don't live in a perfect world, so we rely on the shear force of/between the oil molecules themselves to prevent this contact. If the oil becomes too thin, it will not be able to maintain this facility. Another problem with thin oil, of particular concern to those of us running older style engines, is it will flow out of the bearings more easily, along with leaking from places that might not be such a concern with a heavier oil.  This flow may cause problems with oil pressure, delivery to the extreme parts of the engine and possibly even the ability of the oil pump to deliver the required flow.  The problems with oil leaks are fairly obvious, and the areas these tend to increase in this example are Head Studs, pushrod tube seals, flywheel seal and cylinder bases.

An oil that is too thick will not flow easily through the engine, making it slower to reach parts, and slower to return to the sump.  It will not spray around as easily, hence will have reduced capability to cool the engine.  it also will likely produce more friction.

Exotic Oils and additives:

1. Magnatec, or similar products which claim the oil stays in place to protect your engine upon startup. If this process works, it will mean a layer of oil will be clinging to most parts of the engine, impeding the flow of cooling oil. I don't know if it is still true, but when these were first released they were also known for a kind of gelling effect, to the point where I have seen a stock oil screen effectively blocked. Maybe this factor has been fixed, but probably best kept out of air/oil cooled engines.
2. Slick 50 or Nulon - PTFE additives. Very popular when I was young, with the tests showing a car driven for 500km without any oil! Even if you do try one of these products, don't try that with our air/oil cooled engine.  These were also notorious for producing sludge, which in extreme circumstances could block filters or even oil passages.  Scorched bearings where the PTFE had built up were also common.  It seems no really scientific tests could back up their claims, unless they were paid for by the company in question...  Again there is an added possibility they may interfere with cooling in a VW, so best to steer clear.
3. ZDDP and Molybdenum Disulhphide. These are legitimate additives that produce wear resistance and anti-galling on surfaces that are under extreme pressure and/or temperature. These should be used as prelube on the valve train in particular, and can be used on most parts of the engine as appropriate (e.g. don't pre-lube the cylinders or valve stems.)
4. Engine Flush - not really an additive, but something you should use. If you have just bought a second hand VW or engine, you will probably find the sump full of sludgy black muck from inadequate maintenance by the previous owner. Get as much out as you can, fill the engine with cheap oil and the flush and run per directions. Immediately drain the engine, leaving as long as possible, then fill with your regular oil. If the dipstick looks brown after a week, put another tin of flush through.  Regular oil changes should suffice from here on if you are running air filters, but a flush every time the oil starts to look sludgy shortly after a change is probably a good idea. Additives will get used up or worn off - a clean engine will allow the oil to do it's job most effectively.
5. Synthetic oil.  Not so exotic these days.  I will not go into detail here, but it seems the jury is in and synthetic oil is good for VWs... Except, I do not know of a fully synthetic oil that has a high enough base number for most of us, and the cost is prohibitive. If you want the benefits of a synthetic and are willing to pay the extra, 'cos you love your engine, use a good branded semi-synthetic. Of course I am talking about engine oil here - if you can find a suitable fully synthetic gear oil, use it - I guarantee you will enjoy the results.

So what oil to use? All credit to Gene Berg, single grade oil is extremely rare and expensive these days (but still used in go-karts, go figure?) and I am not convinced it is even a good idea. VW themselves recommended mutigrade oils and specify ranges, but I will provide a little more general advice here. Please remember I live in a failry warm part of the world, don't see sub-zero unless we go skiing, etc:

1. It's just a VW and I drive it. Use 20W50 if you can get it, you might get away with 20W40 if you live in a cooler climate, but if it's really cold you will be using a 15W- or 10W-  The 50 means it will not thin out as much at temperature, and even healthy VW engines tend to run a bit hot.  The 5W might look tempting if you want to go synthetic, but unless you live in Antartica will probably cause a lot of the problems described above.
2. I've just rebuilt my engine, using German Seals and new crankshaft etc.  Use 15W50, with similar warnings to above.  If you have paid attention to bearing surfaces and sizes, bearing crush, etc, you should be OK with a 10W50 - I will try this when I get my engine done.
3. I'm going racing - OK, now you are probably running an oversize oil pump, extended sump, high pressure hoses, etc.  If you can afford it, run the fully synthetic as you want every ounce of power you can find - it may also help keep your monster cool. Don't run a single grade, even if you can get it, as your engine doesn't usually run long enough for it to get to temperature if you go to the drags, and will run too hot for it if you are an off-roader.  If you are dropping your oil after every meet, you might want to save a little and run a semi-synthetic, but otherwise you probably can't afford the sport! Just kidding, lot's of people run dino oil in their drag cars for this very reason, just run the lowest base rating oil that won't leak all over the track.

What about additives?  Oil companies spend a fortune adding pretty much all you require to your oil and you will be dumping the whole lot at 5000km at the most right?  After run in, I'd just run the oil - if you don't think it's enough, spend the extra on a better oil.

The exception being the flush, of course.  Just look at the crud in your engine when you do a rebuild and you will see this makes sense.

One more thing:  A lot of people seem to have forgotten, or don't think it matters with modern cars/oils, but if you do not use your car regularly, do only short trips, or are storing the car you must do extra oil changes.  Ever noted those interesting little indented patterns in your bearings? That is where acid has built up in the oil and sat there etching the bearings.  This exists in all engines, but if the oil is not regularly reaching temperature or it is left for extended periods, such erosion becomes accelerated.

You don't need to change the oil again at the end of it's storage, just before. And if you only drive your car to the shops, enjoy a regular long drive, just to keep you both happy.