Audi 3.7 BFL engine

Technical data

The first Audi gasoline engines with eight cylinders appeared in the late 80s. They were real monsters, having a total of 40 valves, but very reliable and durable.

The first gasoline V8 in the history of the brand was presented in 1988. The EA824 unit with a displacement of 3.6 liters appeared on the flagship Audi V8. Its output was 250 horsepower.

The engine lasted in production until 2006, which speaks about the successful decisions of engineers. In total, two dozen versions of the powertrain were created. In the middle of 1991, there was a version with slightly increased to 3.7-liter volume, and by the end of the year there was a 4.2-liter unit.

Despite the different volume, structurally the gasoline engines are identical, they have an aluminum block, and the cylinders received chemical treatment with caustic sodium with the formation of silicon crystals on the surface. The timing is belt-driven, with a pair of camshafts for each cylinder head, linked by a chain.

As a result of restyling in 1998, the cylinder head was changed, and it became possible to control the timing through the camshaft chain tensioner. At the intake installed a manifold with variable length, and also for the first time began to install two turbines on the motors for the most powerful Audi RS6. Atmospheric versions of the engine were on the assembly line until mid-2006, they were used not only on Audi A6 and A8 sedans, but also on Volkswagen cars – Phaeton sedans and Touareg SUVs.

This review will consider only the 3.7-liter unit used exclusively in the Audi A8. Against the background of a more voluminous 4.2-liter unit, it differs by a shorter piston stroke, but otherwise they are almost identical, even the attachments.

General Engine Reliability

The reliability indicators of the motor are very good, even the aluminum block does not prevent them from passing 500 thousand kilometers. And even after many years of active operation, the condition of the cylinders remains close to ideal. Of course, there are individual censures to any engine, but they are extremely insignificant.

Oil leaks

Faced with oil leaks with this engine can be on the rear oil seal, they are expressed by sweating in the place of connection of the engine with the gearbox. For the front oil seal, as well as the gaskets under the valve cover, is characterized by high reliability and durability.

Crankshaft and camshaft sensors

The position of camshafts in the cylinder head is controlled by sensors, and for the right head its location is provided in the front, and for the left behind, different will be the marking of the sensors themselves. If the left sensor fails, the engine will not start, similarly, the engine will not start if the crankshaft position sensor fails.

Ignition coil

The price tag on the original coils today reaches 240 dollars, but they are characterized by reliability and repairability. If you choose among analogs, then prices will start from $25.

Inlet manifold

For the manifold on the inlet, there are two plastic flaps of great length at once. In motion, they are driven by a vacuum actuator. There are two of them in total, the left one is responsible for the second stage flap, the right one for the third stage. Pulls to the axles of the flaps are also plastic, so their breakage is quite common. The cause of breakage is most often the damper sticking. The rods themselves are sold only together with the actuator with a price tag for each about 400 dollars. As an alternative, you can choose analog parts, make the rods yourself or even just take out the flaps. To exclude the occurrence of a problem, it is worth periodically cleaning the mechanism. To do this is not so difficult, the main thing is to disassemble the manifold itself.

In the case of moving one of the flaps, it begins to slam and often misleads owners, making them think about the occurrence of a malfunction of the engine.

If the flapper retains mobility but does not work properly, the problem may be in the electro-vacuum valves or their connections. In the actuator itself, sometimes the diaphragm ruptures, disrupting its operation.

VGC valve

The crankcase gas ventilation system provides for a valve to be located between the intake manifold and the engine shield. If the diaphragm ruptures, air begins to be sucked into the system through it, causing problems that can be detected by computer diagnostics. The fuel mixture becomes less saturated, as a result of which the engine runs unevenly, there are periodic ignition skips. Air suction is accompanied by a characteristic whistle, especially it is heard at idle, and the oil plug on the engine does not suck. The cost of the valve VKG in the original is not less than 180 dollars, but it will last for 10 years or even more. There are a lot of substitutes on the market, but the service life most often does not exceed one year.

The heat exchanger

The heat exchanger is located on the lower right side of the engine, if in the sump under it formed traces of cooling must change a small rubber pipe and gaskets fixing the oil pump. Occasionally there are situations when cracks appear on the body of the heat exchanger as a result of which there is a mixture of oil and antifreeze.

Transmission timing chain tensioner

The timing belt pulley is connected to the exhaust camshaft, the drive chains are located at the rear of the right side of the right cylinder head and at the front of the left side. For tensioning, a special-shaped hydraulic tensioner with a solenoid is used, inside which there is a small piston that moves vertically along the guide bars. As a result, the camshafts change their position relative to the crankshaft, thus providing a change in the distribution phase.

It should be noted that the hydraulic tensioners on the left and right sides are different, and they will be different for engines of different volumes. Catalog numbers, respectively, they are also different. The average service life of hydraulic tensioners is about 250 thousand kilometers, after which the engine begins to rumble, there are errors in the phase change. Most often the first to wear out are piston sealing rings or guide strips.

The problem is the high cost of the original tensioners, which is 700-1300 dollars. There are plenty of substitutes on the market with a price tag of about 150 dollars, but the level of their reliability is below criticism. In such circumstances, the optimal solution may be to carry out repairs. Specialists of some car services disassemble them, change all the seals, damper, guides. With a high-quality restoration, they will be able to serve long enough.

Camshaft sprockets

One of the problem areas of this reliable car is the rapid wear of the gears of the camshaft rotation chains. And it occurs not always and completely unexpectedly. At first, the chain starts to rustle, and it can even slip off, if the gear teeth disappear to the very base. There is an assumption that when the gears were manufactured, some of them were insufficiently hardened, which ensures unexpectedly fast abrasion.

The replacement of the shafts will be comparable in cost to the cost of the Audi A8 of the 90s. In turn, it is possible to assess the current state of the gears only after preliminary removal of the valve cover from the engine.

The only option is to search for camshafts from the scrap yards, and optimal in quality are considered parts from Audi A8 D2 engines. The fact is that the problem began to appear only with the newer D3, and on older cars the problem is not noticed. For motors with a cylinder volume of 3.7 and 4.2 liters, the shafts will be different, which should be taken into account when buying. The average cost of such a shaft with normal gears on the dismantlers will be about 50 dollars.

The timing belt

The timing belt is located on the front side of the engine and is very long. The process of its replacement is labor-intensive, it is necessary to disassemble almost completely the front part of the car, so the car service must have the appropriate technical base. Similarly, the floor of the car will have to be disassembled if it is necessary to replace the pump or thermostat. Therefore, it is advisable to combine the change of the belt with other types of repair work, so as not to conduct the disassembly procedure several times. When changing the chain, the camshafts are fixed with a special bar.

In general, the replacement of parts with a set will cost owners at least 1 thousand dollars, including elements of the attachment. The frequency of belt replacement every 120 thousand kilometers, and it is necessary to use only quality timing belts with timeliness of change. If the belt breaks, the engine definitely dies.

Head

The quality of the heads allows you not to worry about the occurrence of problems, their cams, rockers, hydrocompensators have good resistance to wear and practically do not break. Problems can arise with the condition of oil caps, you can determine them by the appearance of oil burning in the amount of about 2 liters or more for every 10 thousand kilometers of mileage.

Cylinder block

The aluminosil block has excellent reliability, problems began later in the newer eight-cylinder Audi engines that received the FSI fuel injection system. Reliability is largely due to good cooling and lubrication, and if cylinder scoring occurs, they can always be plated.

Conclusions

Audi 3.7 liter engines for the second and third generations of the A8 sedan are considered today the best of the existing options. At that, motors of later years of release (EA825) with direct injection and replacement of the timing belt with a chain, reliability indicators are already more modest. If we compare the motor from Ingolstadt with similar in volume motors from BMW or Mercedes, then Audi looks very good here.