The 2.5 VW 5 cylinder engine was essentially the replacement for the older 2.0 liter normally aspirated base model engine. It has a 20 valve cylinder head, with variable valve timing. The 5 cylinder configuraton is known for better torque and smoother revving operation than a 4 cylinder. The engine ratio of bore to stroke is undersquare, meaning a smaller bore and a longer stroke (82.5mm x 92.8mm), which also means more torque than horsepower. The first iteration, from January 2005 (BGP/BGQ/BPR/BPS), produced 148 horsepower and 166 ft/lbs or torque. Starting with the 2008 model year of Jetta and Rabbit, (CBT/CBU) the power increased to 168 hp. and 176 ft/lbs. The Beetle did not get the high power engine until the change to the A5 Beetle in 2012, at which time the engine also became available in the Passat. A distinct difference in the top engine cover makes identifying the difference between the early and late versions easy.
This 2.5 VW 5 cylinder engine did not appear in the Audi line in the U.S., although in other countries, the 2.5 is used as a turbocharged high-performance engine in a few Audis. These 2.5 5 cylinder engines are not descendants of the 1980’s Audi 5 cylinder engine as is the Eurovan engine from 1993. Those engines had a timing belt on the pulley end of the motor, and this 2.5 VW 5 cylinder engine has a timing chain system on the transmission end. The castings for both the block and head are very different from the Audi 5 cylinder from last century.
A vacuum pump is used to provide consistent high vacuum for the brake booster. It is located on the transmission end of the cylinder head, whereas the 1980’s Audi engine had a different type of vacuum pump located on the side of the head in some models. The vacuum pump is a notorious source of engine oil leakage, often causing a donkey-sized puddle of oil. Pump removal for replacement or reseal is relatively easy on an engine with a manual transmission, but takes many times longer with an automatic transmission.
Timing Chain Failure Issue with 5 Cylinder Engines
The timing chain system consists of upper and lower roller type chains with tensioners and guides. A significant point is that the intake camshaft gear has a very low included angle, meaning that the chain only contacts the intake cam gear by 8 to 9 teeth, which means that the chain only wraps around the gear by around 70 degrees of the 360 total. Most cam gears are driven by at least 90 degrees of timing chain wrap. This leaves this 5 cylinder engine more prone to skipping timing chain teeth than other motors. To be more specific, the upper chain tensioner can be seen after the cover is removed. When the tensioner rod extends over 25 mm, then the chain system is worn to where the chain may skip teeth on the intake cam. Skipping one tooth will cause the check engine light to come on for a cam position code. The engine will be both hard to start and have low power. At any time in an engine with a very worn timing chain, the chain can skip more than one tooth, which will cause valves to hit pistons, and thus bend said valves and stop running.
When one changes the oil as per the factory recommendation of 10,000 miles, the timing chain is going to get far more wear than on a motor where the oil is changed more often. We generally find that engines that have consistently experienced oil change intervals of 5000 miles or less, and use quality synthetic oil, exhibit almost no timing chain wear at all. For the record, we advise anyone who drives only stop and go or just city driving to change the engine oil at 4000 mile intervals.
SAI Secondary Air Injection Problems with the 2.5 5 Cylinder Engine
Late model engines like the 2.5 liter 5 cylinder use an electrically actuated SAI combi valve, which are not proving to be as reliable as hoped. Some other applications since 2005.5 use the electrically actuated SAI combi valve, but the 5 cylinder seems to have intermittent reliability issues as well as a possible carbon buildup issue. The 5 cylinder SAI combi valve feeds a pipe which delivers air to both ends of the engine, and a carbon buildup inside the pipe can starve one side for air flow, and the restriction can be borderline. The 5 cylinder SAI combi valve itself can have an intermittent problem causing it to fail the readiness self test just once a month or so, which can be very difficult to diagnose, since every time it gets tested, the system works fine.