BMW M51D25TU engine

M51D25TU is an improved version of the M51D25 power unit from the Bavarians. Diesel power unit with a working volume of 2.5 liters is able to develop a maximum power of 143 horsepower. The engine was installed under the hood of the third series of the third generation E36, fifth series of the fourth generation, and seventh series of the third generation E38.

M51D25TU engine specifications

Advantages

Cars produced by the Bavarian concern BMW are quite famous among motorists from all over the world. Motors of the M51 lineup, which includes this engine, was developed to replace the outdated M21 power unit. The working volume of the engine, as well as all its modifications, is 2500 cubic centimeters. The first appearance of a car with this engine under the hood was recorded in 1991.

The previous lineup was known among the concern car owners as rather “sluggish” engines, but this cannot be said about the motors of the new design. In addition to the increase in power and dynamics, greater fuel economy is also noticed, compared to the previous M21 range. The cylinder block of this power unit is made of cast iron, it is characterized by six cylinders, located in one row. A high-strength aluminum alloy is used for the cylinder head.

The camshaft valve train is equipped with hydraulic thermal gap compensators. The timing mechanism together with the high-pressure fuel pump is driven by a chain. High-pressure fuel pump on the M51D25TU engine, as well as on all its modifications, is electronic. The vacuum pump is mounted on the camshaft. The housing, which houses the air filter, is placed along the cylinder head, along the entire length of the power unit, which significantly decorates the appearance of the motor.

Disadvantages

The M51D25TU power unit can become very hot. It is necessary to see if there is no bubbling of antifreeze in the expansion tank. A classic disease of these engines is a cracked cylinder head. You can try to weld the defect, but it will be much better to buy a whole block head.

The engine may start very poorly when the operating temperature is reached, and it may also have floating rpm. Most likely, the problem lies in the high-pressure fuel pump. To fix the problem, you just need to replace the plunger pair, or simply buy a new pump.

An additional supercharger in the form of a turbine serves for quite a long time, and during 200 thousand kilometers it does not provide owners with big problems. After overcoming this mileage, the turbine starts to churn oil, the car will not drive normally. In case of lack of traction, the turbine will have to be replaced with a new one. But there are cases when turbines can go much longer.

If you don’t look at such small faults, the engines are not bad and have a long service life. But given the fuel quality, long age, and relatively poor maintenance, all sorts of problems can occur.

Modifications

M51D25UL is a modification produced from 1991 to 1996. This is the first version of the engine in the M51 range, which was equipped with an additional supercharger MHI TD04-11G-5, operating at a pressure of 0.9 bar. The maximum output of this powertrain is 115 horsepower, and is reached at 4.8 thousand rpm, with a peak torque of 222 Nm at 1900 rpm. This motor can be found under the hood of BMW 325td E36 and 525d E34 cars.

M51D25OL, produced from 1991 to 1996. This is a more powerful variation of the powertrain, which was characterized by a maximum output of 143 horsepower at 4.8 thousand rpm, maximum torque of 260 Nm can be obtained at 2200 rpm. A distinctive feature of the modification is the installation of a MHI TD04-11G-5 turbocharger, which operates at a standard pressure of 1.1 bar, in combination with the standard intercooler. The engine can be found on BMW 325tds E36 and 525tds E34 cars.

M51D25TUUL is a powertrain modification that was designed to replace the M51D25UL, which was produced from 1996 to 1998. A distinctive feature is the installation of a different electronic engine control unit DDE 2.2, as well as a turbine Garrett TB2514. The power of this modification is 115 horsepower at 4.8 thousand revolutions, and at 1900 revolutions develops a peak torque of 230 Nm. The power unit is installed on BMW 525td E39 and 325td E36 cars.

The M51D25TUOL was produced from 1996 to 2000, and was designed to replace the M51D25OL engine. This engine is characterized by the installation of MHI TD04-13T-4 turbine, as well as intercooler. It uses a DDE 2.2 electronic control unit. This combination leads to a maximum power of 143 horsepower, and torque of 280 Nm. The motor was installed under the hood of 325tds E36, 525tds E39 and 725tds E38.

Tuning

It is not a good idea to improve such an old powertrain, so it is better to stay away from it to ensure normal operation. But if you really want to increase the output of the standard engine, you can search for a company that will take on the replacement of the standard software. In this case, you can get a boost of about 30 horsepower. You should not go any further, as there may be problems with the cylinder head.

Technical specifications

This power unit was first placed under the hood of the BMW 325td in 1991, and it was intended to replace the M21 diesel power unit. The cylinder block of the six-cylinder motor was made of cast iron, and the cylinder diameter is 80 millimeters. The block uses a forged crankshaft that provides a piston stroke of 82.8 millimeters. The connecting rods are 130 millimeters in length. The pistons feature a compression height of 39.45 millimeters.

The block is covered by a single-shaft cylinder head, which provides two valves on each cylinder. The intake valves are 36 millimeters in diameter and the exhaust valves are 31 millimeters in diameter. The diameter of the valve stem is 6 valves.

The camshaft drive in this power unit is chain driven. Service life of single-row timing chain with proper maintenance and care it can pass more than 400 thousand kilometers.

The Bosch VE model is used as a high-pressure fuel pump. The engine is equipped with a turbine. In order to minimize the amount of harmful substances emitted into the atmosphere, the modification of this motor is equipped with EGR exhaust gas recirculation system.

This engine is installed on the following models:

BMW 5-Series (E39)