The oddly configured Volkswagen VR6 engine is innovative. The 1992 2.8 VR6 engine has a 15 degree Vee motor, making the cylinders line up in a staggered pattern, with a single head for both banks of cylinders. It went through various transformation to get larger and more powerful, as well as more reliable. Still in use as of this writing, the modern 3.6 VR6 engine has a 10.2 degree Vee. Combined with the other list of upgrades, this effectively makes it one of the smallest engines for its power range ever in a production automobile. All versions use a single cylinder head. Sometimes it as called a Stagger 6. The VR6 engine has many advantages, and a few shortcomings. It is short and compact compared to other 6 cylinder engine designs. The sound is unique, and the power is impressive. The original 2.8 liter motor has grown through the years, and the power output has gone from impressive to incredible. The mileage has followed suit.
This is, and has always been, a chain motor. No timing belt has ever been involved. The dual chain system is on the transmission end of the motor. VR6 engines have a single chain from the crank to an intermediate idler gear, and a double chain from said idler driving the camshafts. It has always been dual camshaft, but there is a complete design change between the 12 valve and the 24 valve VR6 engine versions. The 12 valve version used one cam shaft for each bank, which operated both intake and exhaust valves. The 24 valve version has one camshaft for all 12 intake valves, and an exhaust camshaft that operates all of the 12 exhaust valves. The 24 valve engine also has variable valve timing. This is accomplished using cam gears with internal oil chambers that allow each camshaft to rotate in relation to its cam gear. The system is controlled electrohydraulically with solenoids actuated by signals from the engine control unit (ECU). This allows the engine to vary the cam timing of each cam in relation to the crankshaft. Plus the 24 valve engine has a variable geometry intake manifold. These changes are the essence of modern power and efficiency, meaning more power with better mileage. And it has its limitations. Maintenance is an issue. Old oil and lack of frequent oil changes will gunk up the variable valve system and cause the gears to freeze in relation to the cams. The car becomes undriveable. Let us explain how expensive and inconvenient this situation really is.
The first sign is the noise from the driver’s end of a VR6 engine. A light rattle at or just above idle says something is loose and worn. Perhaps replacing the upper timing chain adjuster may fix or at least extend the life of the chain system. Eventually, a DTC, or diagnostic trouble code, for a cam position sensor appears in the engine control unit (ECU). The check engine light comes on, and a scan reveals a cam position sensor code. Some think replacing the cam position sensor makes sense. In the earlier 12 valve motors, this means the chains are stretched and/or the chain tensioner rails and guide rails are damaged. In the later 24 valve motors, this usually means the cams cannot adjust in relation to the cam gears any longer.
At this stage, nothing short of removing the transmission and replacing the chains, guides and tensioners will fix the issue. Good luck with any other advice. If the problem comes from extreme lack of oil changes, the muck and goo may be clogging the gears, electronic solenoids and maybe lifters as well. Some can be cleaned, some must be replaced. Sometimes we have to remove the head for cleaning or because the headgasket disintegrated due to acrid oil. Sometimes we have to remove the oil pan and oil pump, and clean out all the passageways. The labor times for these repairs vary from 13 to 32 hours of time. First step is to remove the transmission. Ignoring this warning sign will lead to complete chain system failure, which will bent all the valves, if not destroy the entire motor. Probably cheaper to change your oil more often. If you are not already receiving reminders, ask your Service Advisor to get you set up with DemandForce email reminders for services. Don’t forget to change your oil.
The early series 2.8 liter 12 valve VR6 motors were used up through 2000. The second series of the 2.8 liter engine was a 24 Valve VR6 engine. The third series is a 3.2 liter 24 valve VR6 engine. The current series is the 3.6 liter 24 valve VR6 engine. The first series 12 valve motors are the one most prone to timing chain system failure, many due to upper chain tensioner and guide rail. The second series of 2.8 liter 24 valve engines have far less tensioner and guide issues, as those parts were redesigned to be larger and hardier. But the systems for the adjustable cam timing have failures for clogging and for a screen type filter that can break apart and end up inside one or both cam gears. The engine will then only start with difficulty, and won’t rev up, and so the car cannot be driven. Karmakanix has found the 3.2 and 3.6 VR6’s to have far fewer issues, than their earlier cousins. The 3.2 and 3.6 engines got Fuel Stratified Injection in 2005.