j'utilise sur mon karmann de l'huile semi synthétique MORRIS MAGNOL Premium Multigrade 20W50. API SF/SC.http://www.morrislubricants.co.uk/scripts/prodList.asp?idCategory=114
Ci dessous un article (en anglais désolé) concernant les huiles pour nos flat 4 sur le site de MORRIS LUBRICANTS
Lubrication of Classic VW Air-Cooled Engines
(1949 - Late 1970's)
The design and lubrication requirement of the internal combustion engine has changed dramatically since the Benz Patent Motorwagen. Modern engines have to meet ever increasing environmental demands in addition to fuel economy and extended oil drain periods.
The selection of a suitable lubricant for the ?older? design internal combustion engine is at best problematic and at worst surrounded by myth. In any gathering of enthusiasts a discussion on multigrades, synthetics and specifications is guaranteed to draw a hearty debate.
To fully appreciate the chemistries of engine oils, we must first look at the demands placed upon them. In modern engines high fuel prices, environmental concerns and diminishing oil reserves have driven engine design to ever increasing complexity. One of the main contributions was to reduce the power required to pump engine oils. This important advance has necessitated the use of lower viscosities, particularly during start up conditions. VW has adopted this policy with viscosities as low as SAE 0W/30.
The use of low viscosity oils in modern engines with modern metallurgy, machining techniques and design give clearances and surface finishes that can be lubricated by fine oil films however, the use of these products in older engines with relatively rougher surface finishes would result in low oil pressures, increased noise and poor piston sealing. Older engine designs require viscosity ratings of SAE 30, 40 or 50 to ensure the correct oil film thickness on moving parts. The use of monogrades is essential as they are not subject to viscosity changes unlike multigrades, which can shear as they are worked in the engine.
Modern oils now contain ever-increasing levels of antiwear additives, detergents and dispersants. Whilst some antiwear additives are essential in the older engine, increased levels can stop piston rings from bedding in and increased ash levels may lead to bore polishing both of which lead to poor compression and increased oil consumption.
The use of detergents and dispersants are essential to control acidic by-products and suspend varnishes and lacquers so fine filters may remove them. The level of filtration is critical when considering the type of oil to be used in the older engine. Most engines where only fitted with wire gauze strainers that were essentially designed to ensure the pump was not damaged by larger particles from the sump. The use of modern oils in engines fitted with gauze strainers has the effect of dispersing lacquers debris and metal particles throughout the engine, leading to abrasive wear in bearings, blocked oil galleries and eventual engine failure. Only with retro fitting of full flow filters can these effects be negated and the engine fully protected.
Additives of all types also have an effect on engine seals. Modern oil seals are constructed from polymeric materials that are highly resistant to hardening and chemical attack. The older engine will contain are variety of sealing materials largely depending on the age of the vehicle and the last engine rebuild.
In recent times the use of synthetic oils has dominated the development of engine oil technology. Synthetics allow engines to operate under higher loads increased temperatures and deliver rapid oil flow at start up. As with all developments, these fluids have been adopted by the market place and perceived superior to mineral oils. Whilst there are substantial benefits in the use of synthetics, when misapplied the results are moreover increases in consumption and engine wear. The use of synthetics in the older engines should not be considered unless the engine has been rebuilt and machined to modern standards. The fine oil films afforded by synthetics will lead to all of the problems previously discussed.
Given all of the above, the choice of lubricant for the older engine should be a monograde SAE 30, 40 or 50, reduced antiwear, no dispersancy additives and perhaps a small amount of detergency for engine cleanliness.
Morris Lubricants produce a specialist range of lubricants for the older vehicle namely Supreme 30, 40 and 50 and Elite 30, 40 and 50 for Motorcycles. These products have been specially blended to take into consideration all of the above points for the complete protection of the Veteran, Vintage and Classic engines.
The lubrication of the VW, air cooled engine largely depends on the type of engine fitted. Type 4 engines did have an oil filter fitted however, the Type 1 engine where only fitted with an oil screen.
By virtue of their design, air-cooled engines rely on ambient temperatures to maintain correct engine operating temperatures. In hotter climates, increased oil temperatures are common as well as prolonged periods in stationary traffic. To offset the thinning effects of temperature, the correct grade of engine oil is vital. For the U.K an SAE 30 or 40 will suffice however, in warmer climates and SAE 50 should be considered.
Supreme 30 or 40 are the ideal choice for Type 1 engines where the absence of fine filters limits the oil drain interval to 3000 miles. It should also be remembered that Type 1 engines have no proper oil seal at the pulley end of the crankshaft therefore, the crankcase is not sealed from contaminants. The use of modern oils without modifications would seriously compromise the engine as previously discussed.
In Type 4 engines the addition of an oil filter does allow the use of more modern fluids and increased drain times of 5000 miles. Supreme 30 and 40 may also be used in these engines however, multigrades such as Morris Lubricants Magnol 20w/50 or for rebuilt engines Servol High Performance 15w/50 can be used without compromise.
Mr Simon Matthews
BSc(Hons), CCHEM, MRSC, CSci, MEI, AIQA
For Volkswagen Club information visit www.historicvws.org.uk