VR6 Engine: A Staggering Technology

Gear case (3)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 crankshaft to a large gear on the intermediate idler shaft which also drives the oil pump. Another chain from the second smaller gear on the idler shaft goes to cylinder head and drives the camshafts. There have always been two camshafts, but there is a complete design change between the 12 valve and the 24 valve VR6 engine versions. The 12 valve version used one camshaft for each bank of three cylinders, 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 electro-hydraulically 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, but we have never seen that fix anything. 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 can also mean that the cams cannot adjust in relation to the cam gears any longer. But the 24 valve systems for the adjustable cam timing have failures for clogging their gears and solenoids and for a screen inside the cam bridge between the two cam gears 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. For a lucky few 24 valve customers, the cam position code may be cured by just removing and cleaning the solenoids and gears, at which time we eliminate the screen as per a factory TSB (Technical Service Bulletin). This work is all done from the top without removing the transmission.

Mostly 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, depending on the model and severity of the problem. First step is to remove the transmission. Ignoring this warning sign will lead to complete chain system failure, which will bend all the valves, if not destroy the entire motor. Probably cheaper to change your oil more often. Don’t forget to change your oil.

The early 12V and 24V 2.8 VR6 engines were originally designated for use with regular oil. This is mostly just because they are from the era before synthetic oil was mandated. The oil should be changed at a maximum of 4000 miles. All the newer, larger VR6 engines since 2004 specify synthetic oil, which should be changed every 5000 miles. We highly recommend that customers with the 2.8 VR6 Eurovans slowly convert to a blend of synthetic and regular oil to help reduce the persistent timing chain wear issue. The smaller Jetta, Golf and Passat cars could certainly use better oil, but the high load of the van sized vehicles makes it important.

The early series 2.8 liter 12 valve VR6 motors were used up through 1999 – 2000, depending on the model. 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 12 valve and 24 valve 2.8 motors are prone to timing chain system failure, mostly due to insufficient oil changes. Karmakanik has found the 3.2 and 3.6 VR6’s to have far fewer issues than their earlier cousins, possibly because they require synthetic oil. The 3.2 and 3.6 engines got Fuel Stratified Injection in 2005.

Gear case (3)