Engine Oil

Changing the Oil Regularly Is the Cheapest Insurance
for Long Life You Can Give a VW Engine.

See our procedure on Checking and Changing Engine Oil (in addition to the notes on the subject below).


The following of subtopics related to Engine Oil are discussed in this article -


Oil Grade

An engine oil's job is primarily to stop all the metal surfaces in your engine from grinding together and tearing themselves apart from friction whilst transferring heat away from the combustion cycle. Engine oil must also be able to hold in suspension all the nasty by-products of combustion, such as silica (silicon oxide) and acids. It cleans the engine of these chemicals and build-ups, and keeps the moving parts coated in oil. Finally, engine oil minimizes the exposure to oxygen and thus oxidation at higher temperatures. It does all of these things under tremendous heat and pressure.

Obviously if oil gets too thin it will allow metal to metal contact, but if it's too thick it will rob power, since it takes more energy to push it around the engine. And the oil film will not shear easily between metal components, so you get added friction within the oil film. It's all a balance, trying to get the thinnest oil which will still maintain an oil film between the metal components.

Engine oil is graded according to its viscosity - the property of the oil that resists the force that causes the oil to flow; that is, the resistance to the flowability of the oil. The proper viscosity is the single most important criteria of a lubricating oil. The basic performance of machinery is based on the viscosity of the lubricant.

High viscosity oils seem thicker and pour more slowly at room temperature than do low viscosity (thinner) oils. When heated, however, oil loses some of its viscosity. A high viscosity oil heated to 93C (200F) may pour as readily as a low viscosity oil does at room temperature. If an oil has too low a viscosity, it will not maintain an adequate lubricating film between moving parts. A thin, low viscosity oil may maintain this film at low temperatures but become so much thinner after it has warmed up that it leaves the engine parts unprotected.

It might seem that a high viscosity oil is all that is necessary to properly lubricate an engine. Unfortunately, this is not true. If a high viscosity oil is used during cold weather, it will become so thick and resistant to flow that it cannot properly circulate and reach the parts of the engine requiring lubrication. A thick, high viscosity oil will also become so gummy in cold weather that the starter cannot turn the engine fast enough to start it. The proper viscosity oil will remain fluid enough after the engine has cooled to permit easy starting, yet after the engine has reached operating temperature will retain sufficient viscosity to maintain an adequate lubricating film.

Single-grade engine oils, such as SAE 30, were formerly recommended for use in VW engines because of the unreliable quality of the then available multi-grade engine oils. The new high standard for engine oils (set in the US by the American Petroleum Institute - API) has made multi-grade oils suitable for use in the VW engine. Because of these improvements in the quality of commercially available lubricating oils, completely new oil recommendations for VW cars became effective in 1975. The VW Owner's manuals all say "The VW engine makes no demands in respect of engine oil quality which cannot be fulfilled by every well known and popular brand." That's very diplomatic of VW, but in fact the engines were designed to operate in all weather conditions all over the world, so it makes sense not to limit it to any particular brand of oil.

The new engine oil recommendations, given below, should be applied to all VWs. Car owners will find that these high-quality multi-grade oils offer many advantages in convenience, performance, and economy - even in older model VWs.

For example, a single-grade oil may have to be discarded after a short period of service owing to the early arrival of winter temperatures. A multi-grade oil, suitable for both summer and winter temperatures, can be left in the engine until the normal oil change mileage has been reached. This feature of multi-grade oils can save the expense of oil changes necessitated by climatic conditions.

The viscosity grade of oil is designated by an SAE (Society of Automotive Engineers) standard number. An oil designated SAE 40 has a higher viscosity (greater resistance to flow) than an oil designated SAE 30. Multi-grade oils have an extended viscosity range and can be used in place of a number of single-grade oils. For example, an SAE 10W-30 oil is suitable for use within a range of temperatures that would require three different single-grade oils in order to cover it (SAE 10W, SAE 20W/20, and SAE 30). The multi-grade oils available these days are very good, and they make it unnecessary to make the weather-related changes previously recommended by VW. These days most Beetle shops will recommend a good multi-grade oil, say a 20W-50 for general use, and a 10W-30 for snowy winter use. Generally it's better to stay away from the 10W-40s, as they have a higher content of long-chain polymers to get the 40 rating from a thin base, and the polymers are not lubricants themselves.

The chart below shows the proper oil viscosity for VW engines under specific climatic conditions. The SAE viscosity number of the oil should be selected for the lowest anticipated temperature at which engine starting will be required, and not for the temperature at the time of the oil change. Because the temperature ranges of the different oil grades overlap, brief variations in outside temperatures are no cause for alarm.


Ambient Temperature vs Oil Viscosity


Multigrade oils work by having a polymer added to a light base oil which prevents the oil from thinning too much as it warms up. At low temperatures, the polymers are coiled up and allow the oil to flow as its low number (W number) indicates. As the oil heats up, the polymers unwind into long chains which prevent the oil from thinning as much as it normally would. The result is that at 100C, the oil has thinned only as much as it's higher rating. Think of it like this: a 10W30 oil is a 10-weight oil that will not thin more than a 30-weight oil when it gets hot.

The viscosity index (VI) of a lubricant is an empirical formula that allows the change in viscosity in the presence of heat to be calculated. This tells the user how much the oil will thin when it is subjected to heat. The higher the VI, the less an oil will thin at a specified temperature. Multi-viscosity motor oils will have a VI well over 100C, while single viscosity motor oils and most industrial oils will have a VI of about 100C or less. When you see 10W-50 oil, for instance, you know that the '10' and the '50' refer to viscosity of the oil at different temperatures.

The multi-grade designation indicates the reaction of the oil to rising temperature. A 10-weight oil starts out thin and get VERY thin as it heats up, but if some long chain-polymers are added they prevent the oil from thinning out quite as much when it's hot - the oil still gets thinner, but not as thin as a 10-weight oil would be without the polymers. So if the added polymers result in a hot oil which acts more like a hot 30, then it's called a 10W-30. Obviously more polymers would result in less thinning as the oil heats up, so then you get a 10W-40 for example.

Viscosity is measured in centistokes. For example, a cold 20-weight oil has a viscosity index (VI) of about 200 centistokes and will thin to about 15 centistokes at 100C (212F). A cold 50-weight oil is about 300 centistokes at 100C will thin to about 20 centistokes. A 40-weight oil will thin to between 14 and 17 centistokes at 100C; a 20W-50 weight oil will thin to 17-22 centistokes at 100C. So if you take a 20-weight oil and add polymers so it thins from 200 centistokes to 20 centistokes (rather than 15), it becomes a 20W-50weight oil (cold 20, hot 50).

Each number in an oil weight designation covers a RANGE of actual viscosities. Both 40-weight and 50-weight oils COULD be the same viscosity (17 centistokes at 100C). But in general the 20W-50 weight oil will remain a little more viscous at 100C than the straight 40-weight will. In summer when the ambient temperature (and therefore the engine temperature) start to rise, the generally more viscous 20W-50 weight oil will remain a little thicker than the straight 40-weight oil and so will maintain the oil pressure better.

Although the engine can cope with a cold 40-weight oil in summer, a 20W-50 weight oil will still make for easier starting. A straight 40-weight oil is between 120 and 180 centistokes at 40C ambient (the low temperature measuring point), where the 20W-50 weight oil is only 35 to 80 centistokes. In other words, a straight 40-weight oil drops from roughly 150 centistokes cold to 15 hot, whereas a 20W-50 weight oil goes from roughly 50 cold to 20 when hot - better at both ends of the scale.

There is nothing wrong with using a mono-grade oil, of course, but you will have to change your oil more frequently for the weather. During very hot summers (about 38C (100F) for instance, straight 30-weight oil is getting a little marginal, especially in a Bus or Camper which work the engine harder than the Beetle (more heat for the oil to cope with). These days the multi-grade oils are so good it?s a shame not to make use of them for a wider temperature range.

Detergent straight 40-weight oil is getting hard to find. Non-detergent 40-weight oil might still be around for specialty purposes, but these oils should never be used in a Bug engine. All the Owner's Manuals we have read (Rob currently has about six of them from '58 onwards) say that you must use HD oil (that's High Detergent - not Heavy Duty as some folks think). A detergent oil keeps all the crud suspensed in the oil so it's flushed out with the oil change. Non-detergent oils allow the sludge to settle and stick to the inside of the engine casing, etc., and eventually bits of it will break off in chunks and can block oil passages, etc.

Since the lubricants used in your VW have a vital influence on its operation, you should use only name brand oils labeled "For Service SD" (or "For Service SE" or both) in your engine. Oils used in 1975 and later cars must be labeled "For Service API/SE."

In a recent survey, Castrol GTX (20W-50) came out as the favourite. Also, Rob has a VW mechanic friend in Australia who has done a lot of testing of various oils in his own VW Bus, equipped with a good temperature gauge, over many years. He found Castrol GTX 20W-50 ran coolest of all, and that ALL oils gradually increased in running temperatures as they got older (more miles). So he used Castrol GTX 20W-50 and changed it every 2,000 miles before the temperature rise started to happen. He tried an el-cheapo oil on one occasion but found that the temperature rise happened after just a few hundred miles. Castrol GTX 20W-50 is cheap enough to buy, good enough quality, and available all over.

Rob writes - South Australia (like Texas) has a warm climate. The winters rarely get below freezing (0C, 32F) and the summers are hot - over 40C (104F) is common. I run 20W-50 all year round on newer engines and 25W-60 on older engines. The 20W-50 works well down to temperatures of about -5 (23F), so is no problem with the occasional frost.

The reason I use 25W-60 in older engines (in our warm/hot climate) is to improve the oil pressure - the 60 number means it stays a little thicker when the oil is hot. I would not use this higher viscosity oil in cooler climates though - either 20W-50 for cool/warm climates or 10W-30 for snowy climates. I have received good service from Castrol oils, but any good brand will mineral oil will do equally well. Synthetics will work fine too but the higher price and long-lasting capacity is not justified since you still have to change the oil every 3000 miles just to keep it clean.

We recommend steering clear of the cheaper "supermarket" or generic brands of oil. They MIGHT be okay, but sometimes they use cheap additives to meet the SC/SG etc. standards. Since the VW engine runs hotter than its water-cooled cousins (head temperatures of 130-140C (266-284F) rather than 100-110C (212-230F), the oil does get a serious workout, and the oil additives need to be very stable to last the distance. We tried the cheaper oils in our earlier, less-educated days, and the stuff lost that nice oily feel - turned 'watery' in 500-1000 miles, and the engine got tired very quickly. We've stuck to good stuff following engine rebuilds, and the engine is definitely happier for it.

Note: Busses use lower gearing than Beetles, so you could say that 2000 miles in a Bus is roughly equivalent to 3000 miles in a Beetle.

Parenthetically, Rob notes -- I use an Aussie-made high-quality mineral oil called Penrite HPR30 myself. This is a 20W-60 (yes - 60) oil and is recommended by most of the VW shops here in Australia for all Beetles. My engine is getting a bit tired, and this keeps the oil consumption down to a reasonable level. My engine has done 238,500 miles on just one full rebuild (plus one top-end rebuild), so multigrades certainly do work well -- I've been using them since the late-'70s.

Penrite is not available in the US (yet), but if I wasn't using this, I'd be using Castrol. Castrol GTX is certainly fine for air-cooled cars, unless you have snowy winters. It's good down to occasional temps of about -5C (23F), but if it's consistently below freezing then you are better to use a 10W-30 for the colder months (for easier starting more than anything else -- the 10W-30 is good down to about -9C (15F) according to VWs own oil weight chart), then change to GTX (20W-50) for the warmer months (the lower number is the critical number for cold starts).

This 20W-60, when hot, still thins to a viscosity less than a cold 30, so it's within the original specification for the engine. It uses a high proportion of 'Brightstock' as a base oil, which means it doesn't need excessive amounts of polymers to get the upper number. Brightstock is a high viscosity component of the oil distilate fractions, and has a milky appearance, hence 'brightstock' (most oil fractions are clear). This brand also has a high zinc content, which reduces scuffing -- good for cam lobes and tappets where metal/metal contact occurs most.

Bottom line -

A very good quality engine oil in the engine is the cheapest insurance for long engine life in any Beetle. VW engines run hot, so they need good quality oil with stable additives. They have no oil filter, so the oil needs changing every 3,000 miles like a religion. Castrol 20W-50 is very popular in both the US and Australia, and this oil is our recommendation -- it's a good oil at a reasonable price. Consider a 10W-30 when the winter temperatures are consistently below freezing.

For more information, there's an article on the web by Ed Hackett, More Than You Ever Wanted to Know About Motor Oil which is very interesting reading.

Note: The foregoing is adapted from the Bentley Official Service Manual and the wisdom of Rob Boardman.


Oil Additives

It has been suggested to some VW owners by well-meaning mechanics that they run straight 30-weight oil, with a bottle of STP added to it. Adding STP seems counterproductive to us -- why not just use a 40-weight oil if the 30-weight oil needs thickening (which is mostly what STP does.) We wouldn?t add STP or anything else to it - just stick to the straight oil. Rob's VW mechanic in Australia says he's rebuilt lots of VW engines and has yet to find one which has failed because of the type of oil used. But he has found that wear and crud seem higher in cars run on cheap oils and on cars where the oil wasn't changed frequently enough. He says that the cheaper brands seem to get dirty sooner or go 'thin' faster than good brands. It must be remembered that crud build-up in the VW engine can be a problem because of the lack of a filter, and the poorer-grade oils seem to get cruddy faster than the better-quality oils. In any event, it is vitally important that VW engine oil be changed regularly.

The VW Owner's Manual states that "No additives of any kind should be mixed with HD oils."


High-Detergent Oils

The "HD" designation used in describing motor oil stands for "High Detergent" (not Heavy Duty). High detergent oils (of which Castrol is one) help to wash the engine of crud and hold it in the oil so it gets removed with the oil change.

A caution regarding high-detergent oils - it is detrimental to change back to a detergent oil after using a non-detergent oil for a while. The non-detergent stuff will allow a build-up of crud inside the engine, and then the detergent oil will scrub it away (into the oil) so it will get super dirty super fast -- which of course is not good for your engine. VW recommended detergent oils and frequent changes so that the crud is flushed away before it becomes a wear problem.


Synthetic Oils

Synthetic oils are a waste of money in the VW engine. They are excellent oils, but they are designed for modern high-performance engines with extended oil changes -- which means the VW engine doesn't count! Synthetic oils don't get hot enough to make use of the synthetics high stability, and the long lasting properties of synthetics are wasted on a VW engine, since most of them have no filter and you HAVE to change the oil every 3000 miles to keep it clean anyway. With such frequent oil changes, the extra expense of synthetic oils is totally wasted.


Oil Level

Dave's son learned a little lesson about checking the oil. When checking the dipstick he found that it only came up to about half way between the end and the bottom mark -- then he realized that the car was parked on a fairly steep slope, facing downward! He checked it later on the level, and it was fine.

Rob provided some good insight on oil level: The dip stick is near the back of the sump, which is fairly flat/shallow. So the dipstick reads high with the nose of the car high, and low with the nose of the car low. If the oil gets much below the lower mark (car on level ground) the oil light will sometimes flicker in hard cornering because the oil in the 'flat' sump sloshes away from the pick up pipe. If this happens there is less than one litre left in the sump! It is wise to check the oil level often and top it up before the level gets this low. VW engines are designed to burn a bit of oil,too, so most Beetles need a pint or so about half way between oil changes to keep it near the full mark.

Regarding a high oil level - A little overfull is no problem, but too much and you get a lot of oil sloshing into the undersides of the pistons in corners (or even on the straight if it's REALLY overfull). This would increase oil consumption as the oil rings would have difficulty scraping the excess away with each stroke. It also might result in leaking from the ventilation groove in the crankcase behind the engine pulley, and the pulley would then throw it all over the engine bay! Not good!

If the oil is real low it tends to get hotter (less time to cool down in the sump), and of course if it runs out, the engine will survive for a short time as it gets hotter and hotter.


Checking and Changing Engine Oil

Changing the oil regularly is the cheapest insurance
for long life you can give a VW engine.

Again, see our procedure on Checking and Changing Engine Oil.

After all that we've said about oil quality, it isn't the quality of the oil that is most in question -- it's the fact that unless someone custom builds an aircooled VW engine that is completely sealed from the outside environment, contaminants are being introduced into the engine just through normal use.

The VW engine has slots behind the engine pulley and a spiral groove in the crankshaft that results in fresh unfiltered air being pulled into the crankcase for positive crankcase ventilation. That air and any fumes are then drawn up the ventilation pipe and into the air cleaner.

So dust and anything else in the atmosphere is being drawn into the engine and is trapped in the oil. There's no oil filter on most VW engines, so the 3000-mile oil changes are important in cleaning the oil before the crud becomes a problem. It doesn't matter if you use the finest synhetic oil in creation, it will still get dirty unless you have a sealed crankcase and an oil filter. Since the stock VW engine has neither, regular oil changes are vitally important.


A Bob Hoover "Sermonette" on VW Engine Oil

(Paraphrased, with comments from Rob Boardman interspersed.)

Used with permission.

There are some applications where traditional lubricants work best and your antique Volkswagen is one of them.

Volkswagen enthusiasts have come up with a practical means of adapting full-flow oil filtration systems to the VW engine; if properly designed, such filtration systems will essentially double the life of your engine. However, many VW owners hoping to improve their engines have ended up destroying them by bolting on poor quality filter/pump adapters.

Note: Bob stops short of recommending an after-market full-flow filtration system. Having a full-flow filter would be a good thing, but so long as you change the oil regularly I don't think it would double the engine life. The filter would allow some folks to become lazy I guess. Fresh oil is cheap insurance, in my book. In dune buggy and baja applications, a filter would definitely be a good thing. But in a normal street Bug, regular oil changes is the key.

If you use modern high-detergent oil all you need to do is remove the drain plug; you should leave the sump plate alone.

The old non-detergent oils used to allow the fine crud to settle out, and since the sump plate is the lowest point, cleaning it made a lot of sense. And VW wanted this to happen so the later sump plates don't even have a drain plug - you HAVE to remove the plate.

The detergent oils hold the crud in suspension much better, so almost all of the crud comes out with the oil through the drain plug.

I remove the plate and clean the wire mesh filter about every 4th oil change, and I haven't noticed any gunk in the filter screen, and don't get any more than a "stain" of gunk on the sump plate doing it this way. If I lived in a dustier climate I'd change it more often though. Remember that there is an opening into the crankcase around the pulley shaft which is designed to pull in fresh air (unfiltered!) so it is certainly useful to clean the sump plate occasionally - it WILL get some crud on it eventually.

Things go awry right off the bat because typical sump gaskets sold today are permeable cardboard instead of resin-coated non-permeable gasket material. In plain language, they are unsuitable as oil gaskets; they leak. That means you have to spray the cardboard jobbies with a non-hardening sealant.

Note: (Neither Rob nor Dave have ever done this.)

The other thing folks do wrong is to NOT replace the crushable copper washers on the sump studs and drain plug.

Note: Rob writes - I don't remember ever needing to replace this washer. I suspect that mine is still original. I'm very careful to snug the plug home without overtightening, so maybe I've been doing it just right or something. It doesn't leak anyway.

Fortunately, Toyota and Nissan both use crushable sealing washers on their sumps, including one size that fits the VW drain plug.

Note: That's useful to know. What would be ideal would be a washer that is soft enough to seal but keeps it's shape.


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