The BMW M60 V-8 and BMW M52 6-cylinder engines (the M52 Nikasil engine never went to the USA) with Nikasil cylinder bore linings are particularly vulnerable to fuel (gasoline or petrol) with a high sulfur content.
The sulfur in the fuel breaks up the Nikasil lining in the cylinders, thus causing a loss of compression. Once the lining is damaged, excessive bore wear of the soft, underlying alloy occurs very quickly. Some Nikasil engines have failed in as little as 30,000 miles. And the effect is cumulative, so if the engine has ever been run on high sulfur fuel, the damage may already have been done and premature bore wear may result.
Some symptoms of the Nikasil problem are rough running at idle and difficult cold starting, both due to loss of compression. In severe cases, the loss of compression is so bad that the engine loses power. Oil consumption increases dramatically as oil is sucked up the side of the leaky pistons. In extreme cases, the compression decrease is so severe the car will not start in cold weather, especially M52 6-cylinder engines.
Over the years, BMW has provided replacements with steel, cast-iron or Alusil lined engines, at considerable cost to the manufacturer. Often, disgruntled owners have borne the brunt of these replacement costs, and prospective buyers are at risk, too.
The Nikasil coating process was developed by the German firm Mahle, originally for use in the Mercedes Wankel rotary. Audi, BMW, Ferrari and Jaguar have all used Nikasil engines in their production cars. Porsche used Nikasil in their turbocharged 917 - 935 series of race cars. In racing two strokes, both Morbidelli and Rotax have had great success with Nikasil. Nikasil has been used in thousands of professional grade chainsaws, motorcycle and marine engines, and even many NASCAR Winston Cup and Formula One engines.
Nikasil has been used in high performance engines because it allows the total elimination of poor-cooling cast-iron, and it is harder and more oleophilic (oil-liking) than cast-iron. Nikasil offers superior lubrication, reduced friction, and superior wear characteristics.
The Nikasil cylinder coating is a nickel and silicon carbide matrix coating about 0.07mm (.0025-.003") thick. The Nikasil treatment coats a layer of nickel-silicon carbide, usually by electrolytic deposition, to the inner surface of aluminum cylinders. The nickel matrix is very hard, yet it is relatively ductile. Dispersed through the nickel are particles of silicon carbide less than 4 microns in size. These extremely hard particles make up 4% of the coating and form a multitude of adhesion spots where oil can collect. Beside providing a long wearing surface for the piston and rings, the silicon carbide particles contribute to longer engine life by ensuring good cylinder lubrication.
So why is there a problem? BMW reportedly did not discover the problem with Nikasil in their original testing because they used only high-quality fuel. Sulfur should be extracted from fuel before it is used, but since it is a costly process, oil companies may not remove as much as they should. Once BMW was aware of the Nikasil crisis, BMW replaced the cylinder blocks and also tried to ameliorate the problem by re-programming the DME to ensure higher combustion temperatures.
What to Do
Check your engine. Only the M60 and the European M52 engines are affected.
The M60 was fitted to all the E34 530i and 540i V8 cars. It was not fitted to the earlier E28 5 Series or the later E39 5 Series. Also, the early E34 3.0 cars (pre-1991) were M30 powered 6-cylinder cars and were not affected.
The M52 was fitted to the European E36 3 Series, E34 and E39 5 Series. The early models had the M50 (no VANOS) engine, and the later ones had the M54 (double VANOS) engine. It is only the European single VANOS M52 units that were affected, and even then, not all of these engines were affected.
Check the casting number on your engine. As reported by Koala Motorsport, the M60 Nikasil engines are:
|M60B30||1 725 970 or 1 741 212|
|M60B40||1 725 963 or 1 742 998|
On the M60 block, the casting number is stamped on the engine, on the right side of the car directly alongside the 3rd cylinder, and slightly above the coolant drain bolt.
Take the vehicle to a qualified mechanic for a "leakdown" compression check. The leakdown test detects a lack of effective sealing (loss of compression) in one or more cylinders.
If you take the vehicle to a BMW dealer, the mechanic can quickly check the idle quality using a BMW diagnostic computer system. BMW extended the warranty on Nikasil engines up to 6 years or 100,000 miles, whichever comes first.
Remember, the higher the octane, the lower the sulfur. If the previous owner had always used high octane fuel, then you may never have a Nikasil problem. Beware if the prior owner always bought the cheapest fuel!
Because of the quality of the fuel in certain locations, some areas are more likely than others to have high sulfur fuel. Unfortunately for BMW, the USA and the UK are two of these areas. These also happen to be two of BMW's largest markets! Incidentally, Germany and Continental Europe appears to be largely unaffected by the Nikasil problem.
Everything else being equal, if you are in the market, you want a car with an Alusil engine (the M62).