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Books have been written addressing this well discussed, seemingly simple question.
But, it’s not a simple answer. So let me (try to) confine my answer to the peculiarities of air cooled (VW) engines.It is very important that you understand that our engines were designed some 75 years ago and oil is much different now than it was. Synthetics didn’t even exist then. Multi-grade was unheard of.
“Everybody” (I’m talking shadetree mechanics here) ran straight 30 weight oil. Until the engine started smoking and then they changed to straight 40 until, at end of life, they went to straight 50.
These oils were thick out of the bottle (can) and our electrical systems struggled to turn the engine over in cold weather starting conditions. Multi-weight oils are much thinner and allow better lubrication when starting (cranking) since the oil flows more readily to all the remote components more quickly.
An understanding of how VW’s oil temperature regulating system works is important. VW engineers knew that thick oil meant cold engine (single viscosity – right). So, they put a “pressure regulator” right in the oil flow circuit immediately after the oil pump. This spring loaded regulator prevents oil from going through the oil cooler if the oil pressure is too high (because high oil pressure means/meant the engine was cold). So, if you use oil that is too thick in an air cooled engine, it will not only cause more wear on initial startup and more internal drag on the engine since it is trying to pump that more viscous fluid throughout the engine BUT it will increase engine operating temperature when warm. Why? Because the oil is prevented from going through the oil cooler when the oil pressure is too high. DO NOT RUN OIL THAT IS HEAVIER IN VISCOSITY THAN YOU NEED.
I like the multigrades and run Valvoline VR1 Racing oil with ZDDP. 10W30. (The stuff in the silver bottle.) I believe that the standards pretty much eliminate the differences between different manufacturers but run Valvoline because it has extra Zinc (another discussion subject) and I’m old. (Just about the same age as air cooled VW engines). If my engine started to smoke (blue smoke, not black) I would go to 10W40.
(If you think that the viscosity of 10W30 is the same as 10 when cold or 30 when hot, check the charts. The answer is interesting.)
I could write for a few more pages on this subject but it’s time for breakfast.
Royal2015-11-20 08:25:15
I played with oils for a couple of years . A discussion with a member of TD replica we both felt that 20 w 50 Brad Penn (high zinc) was the best choice .Lucas was a close 2nd but expensive . No synthetics they ran hot
Which is better, Ford or Chevy?
I’ve owned over 30 air-cooled VWs over the years, worked in a couple VW shops part time, and in general agree with Roy’s points. In the years before synthetics, most street VWs were recommended to use Castrol 30w and avoid multiblends due to heat tolerance (air-cooled engines run much hotter than water-cooled). Racing oils like Lucas, Brad Penn, and Royal Purple are good also, but expensive… ZDDP anti-wear additives are important, but the “clinginess” of synthetics offset this need, for the most part, addressing the issue that by far the most engine wear occurs on startup, in the few seconds before pressurized oil gets pumped through the system. Once you have oil pressure, there is little metal to metal contact – everything is cushioned by a thin layer of oil.
Couple additional thoughts, somewhat unique to these engines.
1. These engines are designed to operate at relatively low oil pressure. The stock oil pressure relief valve Roy describes is designed to bypass the oil cooler at approximately 42-45 PSI to prevent blowing seals or tubes in the oil cooler. Thick oil can make them run hotter because the oil is bypassing and not being cooled. There’s a whole separate discussion about the importance of making sure the factory thermostat and cooling system is complete and operational that I won’t digress into – it is designed to warm up the engine quickly, and keep it at optimal operating temps.
2. This simple engine has no oil filter, only the screen on the oil pump, so the oil change interval is at no more than 3,000 miles. But, that’s a lot of miles/fun for a warm weather “Sunday driver.”
3. But, another enemy of engine longevity is moisture/humidity in the oil, which makes it become acidic, and causes pitting which can then lead to increased wear. This engine has no PCV valve and crankcase pressures are most often vented to the outside air through the small metal tube that goes down beside the generator/alternator stand. (There may or may not be a hose from the top of the generator stand besde the oil fill cap to your aftermarket air cleaner). There is supposed to be a rubber nipple on the lower end of that metal tube that allows pressure to escape, yet automatically closes to prevent dirt/dust AND moist air from being drawn up into the engine as it cools. This nipple is very often missing. The top fitting, where the rubber hose would be routed to the air cleaner should never be just left open. If your air cleaner has no provisions for the breather hose, then cap that fitting or route a hose to separate aftermarket oil breather box. Leaving it open, uncapped allows the engine to suck in moisture and contaminants into the engine as it cools. Then, pay close attention to the underside of the oil filler cap, and wipe it clean at every oil change (at the least). If you see any white/yellow foamy buildup on it, that’s an indication that you have moisture (and acid) building up in the oil. It needs to be changed, regardless of how many or few miles you have on it. On a related note, I like to change the oil in the fall, every fall, before it goes into winter storage to avoid it being stored with acidic oil in it. Then, it’s ready for the first warm, spring day. If I drive enough to require a mid- or late-summer oil change, so be it, it will still get get changed again before storage.
4. The factory oil pressure light is designed to come on when the oil pressure drops below about 7psi. It is common for this light to flicker on occasionally at idle when the engine is hot and you’re idling at a stoplight, for example. But if it glows a steady bright green or is slow to go out when you drive off, that’s an indicator that your oil is too hot, and consequently too thin. Using a SLIGHTY thicker oil, such as 10w40 instead of 10W30 should be considered. IMO, never use an oil higher than 4O or you risk bypassing and overheating. I like to use an oil pressure gauge in addion to the light, and ideally see warm engine oil pressures in the 10-35psi range.
Philosophically, I’m more concerned with having clean oil in this unfiltered engine with an open ventilation system than I am about the specific properties of more expensive specialty oils. IMO, a decent quality oil changed at 2,000 mile intervals is better than a more expensive oil changed at 3,000 mile intervals…
I’d try a 10W30 synthetic blend, and if your oil light stays on frequently, move up to a 10W40…
My 2 cents…KentT2015-11-20 14:09:12
Early FF TDr on 69 VW pan
Slowly coming back from the ashes...Royal wrote:As usual, Kent knows some s*** about these engines. However, and I know that Kent knows this, the pressure regulator closest to the pulley on dual relief engines (1970 and later) does not protect the oil cooler from overpressure, it simply blocks the inlet to it effectively taking it out of the circuit. It remains pressurized by the oil in the outlet side of the cooling tower. So, and I have heard many, those who brag that they have 50# pressure (and up) are standing into danger of blowing an o-ring seal to the oil cooler or worse yet rupturing the cooler. The second relief (the one closest to the flywheel) is designed to dump excess oil directly to the sump when an overpressure situation occurs. (Note that engines 1969 and prior do not have this second relief so your oil cooler is not protected against overpressure.) Overpressure can be caused by thick oil (stick with the 10W-XXX) and avoid going to a much larger oil pump. My recommendation is 26mm or less.And one other suggestion: When Kent speaks, listen carefully!
The all. I almost made a bad mistake. I’m all school and was thinking 30 weight oil. Glad now that I asked first…
My car is equipped with an aftermarket oil filter. Also, I’m in Las Vegas. The car is garaged and has no heater, so it won’t be driven much in temperatures below 50. Nor would I anticipate torturing myself by going out when it’s much over 90, let alone when it’s 115. Would any of this make any difference in the recommended oil, or in the oil change interval? I don’t anticipate putting more than a couple of thousand miles a year anyway, and was planning on once-a-year changes. As little oil as there is to change, I was also thinking of full synthetic for the maximum lubrication, and to use 20W-40 instead of 10W-40 because I’ll never really be facing cold temperatures.
Yep, Roy. I just didn’t want to write a book, though it looks like I wrote a chapter any way, once I posted it…
In warm climates, that 20W40 should work well, or even a 15w40 if you can find those weights. 10w30 and 10w40 are common. I would not recommend 5wXX unless you’re driving in Canadian winters, nor do I like the common 15w50 or 20w50 due to potential bypassing and overheating. Every engine is a bit different due to tolerances and wear on bearings (especially cam bearings) and the oil pump (both size and wear). Low oil pressure is easy to detect with the idiot light, but high oil pressure is not – it requires an accurate gauge. I recommend 10w30 because it is a safe starting point…
Note these engines are also known to leak and drip a bit, similar to old Harleys and “mark their spot.” Thin synthetic multiblends tend to leak and drip a bit more than straight-weight or dyno oils. So, if you use a 10w30 synthetic and it drip too much, changing to 30w non-synthetic dino oil MAY help reduce that a bit. You’re really not getting longer service intervals with synthetics in these engines, only improved lubrication on start-up and perhaps a bit better heat tolerance…
Again, my opinions – your mileage may vary…KentT2015-11-20 16:59:56
Early FF TDr on 69 VW pan
Slowly coming back from the ashes...Thinsetics are ‘spensive. You gotta change oil in these engines a lot (unless you have a full-flow filter). So synthetics don’t make a lot of sense.
ZDDP is in “race” oil like the Valvoline and Brad Penn. Also in some Diesel formulations–though those may not be ideal in our engines.That said, the ZDDP is made for high-wear, high-pressure parts–solid lifter cams is the usual example. The stock Type 1 is a solid cam but the valve springs in a stock motor don’t press down all that hard. If you do regular multi-grade 10-30 or 10-40 the engine won’t die cuz of it. At least not for a very long while.Bottom line: change the oil every 2000 or 2500 miles. Use oil. Oil oil oil! Make sure it’s in there. Beyond that, don’t worry too hard.–OK and also remember: you only use about 2.6 quarts. Don’t go dumping 4 in there…edsnova2015-11-20 20:56:09
This is an especially thorough article on oils. (Realizing that our air cooled VW’s run at higher temps and are older and not as close tolerances as many or most modern engines.)
https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/
This is an especially thorough article on oils. (Remembering that our air cooled VW’s run at higher temps and are older and not as close tolerances as many or most modern engines.)
https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/
Royal2015-11-20 22:04:34
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