BMW VANOS explained: how variable valve timing works

BMW VANOS is one of the technologies that made BMW engines famous for strong torque at low rpm and great power at high rpm. The name comes from the German "variable Nockenwellensteuerung", which means variable camshaft control.

In this article we explain in simple words how VANOS works, the difference between single and double VANOS, why BMW M engines use a high-pressure version and which problems owners should know about.

Why engines need variable valve timing

An engine breathes through its valves. The camshafts open and close the intake and exhaust valves at exactly defined moments. In older engines, those moments were fixed by the shape and position of the camshafts, and the engineers had to choose a compromise.

Timing that works well at low engine speed gives good torque and a smooth idle, but it limits power at high rpm. Timing that works well at high rpm gives a lot of power, but the engine feels weak at low speed and idles roughly. Racing engines are tuned for high rpm, normal road engines for low and medium rpm.

Variable valve timing removes part of this compromise. By turning the camshaft slightly relative to the crankshaft while the engine runs, the computer can change when the valves open and close. At low rpm it chooses timing for torque and clean combustion; at high rpm it chooses timing for maximum power.

The benefits are real and measurable: more torque across the rev range, more power, smoother idle, lower fuel consumption and lower emissions. That is why almost every modern petrol engine uses some form of variable valve timing today.

Single VANOS

BMW introduced VANOS in 1992 on the M50 straight-six engine, used in the 3 Series and 5 Series. This first system worked only on the intake camshaft and is called single VANOS.

The VANOS unit sits at the front of the intake camshaft, between the camshaft and its drive sprocket. Inside there is a piston with helical splines. When engine oil pressure pushes the piston forward or back, the helical splines turn the camshaft a few degrees relative to the sprocket. A solenoid valve, controlled by the engine computer, decides where the oil goes.

The early system had only two positions, so the timing was either advanced or retarded. Later versions became continuously variable, which means the computer can choose any position within the range and adjust it all the time, depending on load and engine speed.

For drivers, the effect was a noticeably stronger mid-range and a smoother engine. Single VANOS was a big step for BMW and appeared on many popular engines in the 1990s.

Double VANOS

The next step was to control the exhaust camshaft as well. This is called double VANOS. It first appeared on the S50B32 engine of the European E36 M3 3.2 in the mid-1990s, and later on many normal BMW engines, such as the M52TU and M54 straight-sixes.

With both camshafts adjustable, the engine computer can also control the overlap, the short period when the intake and the exhaust valves are open at the same time. More overlap at certain loads helps to push exhaust gas out and draw fresh air in; less overlap gives a stable idle and clean combustion.

Double VANOS can even recirculate a small amount of exhaust gas inside the engine, which reduces emissions without an external system. At the same time, it widens the torque curve, so the engine pulls strongly from low rpm and still revs freely.

For the driver, a good double VANOS engine simply feels strong everywhere. You do not need to rev it hard to make progress, but it rewards you when you do.

High-pressure VANOS in BMW M engines

The engines of BMW M cars rev much higher than normal engines and need very fast and precise camshaft adjustment. That is why several M engines use high-pressure VANOS.

In the S50B32, the S54 of the E46 M3, the S62 V8 of the E39 M5 and the S85 V10 of the E60 M5, a separate high-pressure pump raises the oil pressure for the VANOS system far above normal engine oil pressure. With this pressure, the camshafts can be moved extremely fast, even at very high rpm.

This is part of the reason why these engines combine strong torque with the ability to rev to 8,000 rpm and beyond. The S54 in the E46 M3 makes 343 hp at 7,900 rpm from 3.2 litres, without a turbocharger, and still pulls cleanly from low rpm.

The downside is complexity. High-pressure VANOS units, pumps and solenoids are precise and expensive parts. They need clean oil and correct maintenance, and repairs require specialist knowledge.

Common BMW VANOS problems

VANOS systems are generally reliable, but age and mileage take their toll. These are the most common faults:

• Worn seals. Many older VANOS units use rubber or plastic seals that harden with age. The unit then leaks oil pressure, reacts slowly and the engine loses some low-end torque. A rattling noise at idle, especially when warm, is a typical symptom on M52TU and M54 engines.
• Faulty solenoids. A sticking solenoid valve can cause rough idle, hesitation and fault codes.
• Sensor problems. The camshaft position sensors tell the computer where the camshafts are. When a sensor fails, the engine may run in an emergency mode.
• Loose bolts on M engines. On the S54, the bolts that hold parts of the VANOS hub can loosen over time. Specialists often recommend checking and securing them with improved parts.
• High-pressure pump wear on some M engines, which leads to VANOS fault messages and reduced power.

Typical symptoms are a loss of power at low rpm, rough idle, higher fuel consumption, a rattling noise and warning lights. A diagnostic tool can usually show which part of the system is not working.

How to keep VANOS healthy

VANOS depends completely on engine oil. Clean oil at the correct level and viscosity is the most important thing for a long life.

• Change the oil regularly and use the oil that BMW specifies for the engine. On M engines with high-pressure VANOS, many specialists recommend shorter intervals than the official ones.
• Check the oil level often. Low oil level affects the VANOS system long before it damages the bearings.
• Fix small symptoms early. A rattle or a fault code is cheaper to repair before parts start to wear each other.
• Use quality parts. For seal kits and solenoids, choose reputable suppliers. Cheap parts often fail early.
• Let the engine warm up. Cold, thick oil reaches the VANOS units more slowly.

VANOS is one of the reasons BMW straight-six and M engines feel so special. With good maintenance, it keeps that character for many years and many kilometres.

VANOS at a glance

Item	Details
Name	VANOS: variable Nockenwellensteuerung (variable camshaft control)
Introduced	1992, M50 straight-six (intake camshaft)
Double VANOS	Intake and exhaust camshafts, from the mid-1990s
High-pressure VANOS	S50B32, S54, S62 and S85 M engines
Main benefits	More torque and power, smoother idle, lower consumption
Typical symptoms of faults	Rattle at idle, rough running, weak low-end torque
Main maintenance point	Clean oil at the correct level and grade

Frequently asked questions

What does VANOS stand for?

VANOS is short for the German "variable Nockenwellensteuerung", which means variable camshaft control. It changes the timing of the camshafts while the engine runs.

What is the difference between single and double VANOS?

Single VANOS adjusts only the intake camshaft. Double VANOS adjusts both the intake and the exhaust camshafts, which gives more control over torque, power and emissions.

What are the symptoms of a bad VANOS?

Typical symptoms are a rattling noise at idle, rough running, less power at low rpm, higher fuel consumption and fault codes or a check engine light.

Can I drive with a faulty VANOS?

The engine usually still runs, but with less power and poorer economy. It is best to have it diagnosed soon, because some faults can get worse and damage other parts.

Do BMW M engines use a different VANOS?

Several M engines, such as the S54, S62 and S85, use high-pressure VANOS with a separate pump. It moves the camshafts faster, which helps these engines rev very high.

Sources

• BMW Group – BMW engine technology and history of VANOS
• BMW Group PressClub – technical information on BMW M engines
• BMW Group Classic – engine history