Subaru EJ25 2.5 engine

Subaru EJ25 2.5 engine specifications

Subaru EJ25 Engine Troubleshooting and Repair

Subaru EJ25The largest member of the EJ family was released in 1995 and carried the designation EJ25, subsequently this motor was widely used in all major car models. The Subaru EJ25 engine used the same aluminum cylinder block with dry cast iron liners that was used in the EJ20, but the cylinder diameter was increased from 92 mm to 99.5 mm, the height remained the same (201 mm). It was installed a crankshaft with a piston stroke of 79 mm, instead of 75 mm on the 2-liter counterpart. The length of connecting rods remained the same 130.5 mm, and the compression height of the piston decreased to 30.7 mm (was 32.7 mm). All this made it possible to get an operating volume of 2.5 liters.

The first variation of the EJ25D used twin-shaft cylinder heads (DOHC) with 4 valves per cylinder. The timing drive is belt-driven, timing belt replacement is necessary every 100 thousand kilometers. Power of EJ25D is 155 hp at 5600 rpm, since 1997, the pistons have been changed, and the power has risen by 10 hp.

This motor was put until 1998, and later it was replaced by a more modern engine EJ251. This powerplant belongs to Phase II and is equipped with a new cylinder head, one camshaft on each (SOHC), and new molybdenum-coated pistons, compression ratio increased to 10.1. EJ252 engines were also produced, which meet the increased environmental standards of the state of California and differ in intake, throttle body, idle valve location and DAD.

In 1999, the next type of 25th – the engine EJ253, with the DMRV instead of DAD, in the intake manifold of this engine appeared Tumble Generator Valves, which helps to improve environmental performance. Since 2006, the i-AVLS system, which changes the height of intake valve lift, has been used. In 2009, the engine was slightly improved, after which it received lightweight pistons, modified intake ducts, plastic intake manifold, other spark plugs, improved i-AVLS system, lightened exhaust system.

In 1998, the twin-shaft EJ254 with DOHC cylinder head, the successor to the EJ25D, was also released in Phase II. The motor used the AVCS system on the intake camshafts.

The EJ255 engine became available on the Forester, Impreza WRX and Legacy from 2004-2005 and was a turbocharged motor with a semi-closed block, DOHC cylinder head and AVCS intake camshaft timing system. The compression ratio on the EJ255 is lowered to 8.4 units, TD04L turbo is used, and the boost pressure is 0.8 bar. This makes it possible to remove 210 hp at 5600 rpm. On the other version, the supercharger was increased to 0.93 bar, a larger intercooler was installed and 230 hp at 5600 rpm was removed. Also on the EJ255, for the Japanese Forester STI, was a VF41 turbo. The WRX III was fitted with a VF52 turbo, blowing 0.92 bar. The Legacy GT until 2009 was fitted with a VF46 turbo (0.95 bar), which provided 250 hp at 6000 rpm. After 2009, the Legacy GT was fitted with a VF45 turbo (0.87 bar pressure), which added another 15 hp.

WRX STI versions used EJ257 engine with semi-closed cylinder block, other pistons under compression ratio of 8.0, modified cylinder head with other combustion chambers, c system AVCS. On this engine is a turbine IHI VF48 (boost pressure of 1 bar), it is enough to remove the power of 280 hp at 5600 rpm. In EJ257 for WRX STI III compression ratio of 8.2, added AVCS system on intake and exhaust camshafts, power increased to 300 hp at 6000 rpm, torque 407 Nm at 4000 rpm. The American STIs use IHI VF39 turbos, with a boost pressure of 1 bar.

In addition to the EJ20 and the EJ25 itself, the EJ series included the EJ15, EJ16, EJ18 and EJ22.

Since 2011, the atmospheric 2.5-liter EJs have been replaced by the FB25 and the turbocharged ones by the FA20.

Problems and shortcomings of Subaru EJ25 engines

Since the release of the first version of the EJ25, engineers continued to pay great attention to it, offering the market new modifications and thus bringing the structure and characteristics of the motor to perfection. The motor and its “sore spots” are thoroughly studied, so its owners are not frightened by expensive repairs and maintenance.

Clap covers

Due to the fact that the element is installed on rubber gaskets, over time oil begins to ooze from under them. To solve the problem, you need to renew the cover gasket and the gaskets on the plug wells.

Valve adjustment

This procedure should be carried out every 100 thousand kilometers, checking the thermal clearances. The norm of clearance for intake valves is 0.2 mm, and for exhaust valves 0.25. Checking is carried out with a feeler gauge, and for adjustment you will need only a screwdriver and a wrench for 10.

Timing belt

This element is subject to replacement after 105 thousand kilometers, and it is better not to delay the service. If the replacement date is already approaching, and a knocking sound is heard from under the hood, it is likely that the hydraulic tensioner of the timing belt is worn out. It must be replaced, and also pay attention to the attachment site, which is also subject to replacement – here you can find a workout. The replacement process, despite the device of the engine, is not characterized by high complexity.

Gasket cylinder-head gaskets

Many people associate this part with an unpleasant and quite serious problem, which was first detected on the 2.5 liter engines of 1996. Here, owners of Subaru atmospheric engines were faced with both cylinder-head gaskets puncturing. The fault was first discovered in the EJ25D, where gases escaped into the cooling jacket and in some cases even punctured radiators and expansion tanks.

Things are slightly different in a Phase 2 motor with a single camshaft cylinder head. Here the problem manifests itself in the form of antifreeze leakage. In this case, it can flow not only outside, but also into the sump. Of course, it is not worth speculating about how quickly in this case the engine will “die”.

In this case, the problem is observed on all Subaru atmospheric engines with a volume of 2.5 liters, which were released up to 2012. The most interesting thing is that the problem is not in the structure of the motor or overheating, but in the quality of the gaskets used.

The problem motors were equipped with thin gaskets with an extra protective coating of graphite. Over time, the coating simply wears off, causing the tightness of the element to be compromised. If this problem has already affected your motor or you want to prevent it, we recommend replacing the gasket with a multi-layer gasket (part no. 11044AAA642 or part no. 11044AAA643), which is used on the turbo version.

Of course, the same problem will be faced by those who simply allowed the engine to overheat, but here the culprit is the owner of the car.

Oil pump

It is impossible to bypass the oil pump, located on the front of the engine and driven from the toe of the crankshaft. Oil intake occurs through a special intake channel, passing through the left side of the cylinder block. The support line from the pump is conducted to the oil filter, from which the fluid flows to both half-blocks.

As soon as the system pressure reaches the 5.5 bar mark, the pressure reducing valve is activated. However, the design of the oil pump is quite complex, so excess fluid does not go into the oil pan, but back into the system through the intake channel.

Many owners of these motors find that when the EJ25 is running at extreme speeds, the fluid is converted to a bubbly state at the oil intake point, leading to oil starvation in the 4th cylinder. Some experts suggest making an additional hole in the oil pump so that the pressure reducing valve immediately sends excess fluid into the sump.

At the same time, there are motorists who inflate these motors up to 1000 hp, and even in this case, no one cares how effective the oil pump works – it is left in the stock.

It is important to remember that the turbocharged EJ225 and EJ257 engines, as well as the atmospheric EJ25, have a problem with the fourth connecting rod liners rotating. However, the issue here is not the oil foaming, but the design of the system. It is almost impossible to solve the problem, as increasing the pump capacity will only lead to additional heating of the fluid. Only customization of the part will make it possible to put a final stop to the problem.

Crankshaft oil seal

Another small portion of worries and problems was caused to Subaru owners by the oil pump. The thing is that the front crankshaft oil seal is located in the oil pump. Due to the fact that its back cover does not tightly adhere to the body, over time, oil starts to flow out of there, for which the engineers even provided a special hole, diverting the leak into the oil pan. Under no circumstances should you drill an additional hole here, because this will lead to additional pressure on the oil seal.

If you see oil leaks in the area of the front oil seal, it is recommended to tighten the rear cover of the oil pump, and for better fixation of the screws, use a thread locker. Sealant will not help here, and most likely will even harm it by getting into the oil pan. To prevent more serious problems, it is also recommended to check the clearance between the rotor and cover, rotor and stator, as well as between the rotor teeth (0,02-0,07 mm, 0,25 mm and 0,2 mm respectively).

If the clearances are not within the permissible values, there may be a risk of friction between the pairs, which is particularly bad for the 4th connecting rod.

Cylinder block

Atmospheric EJ-engines, as well as turbo version EJ205 received a cylinder block with an open type of cooling. Closed jacket, on the other hand, was used on earlier turbocharged engines. There is also a cylinder block with a semi-closed contour, introduced in 2001, where the open jacket used baffles in order to increase the strength of the element.

The cylinder block is represented by forged crankshafts, which differ in size between the 2-liter and 2.5-liter versions. The same fact determines the different diameter of the cylinder block and the stroke of the pistons.

Oil intake

The EJ25 engine is famous for breaking off the oil intake tube, and it breaks at the very top. If the tube breaks off on the move, the engine will knock almost instantly. It happens that the tube breaks, then the low oil pressure indicator lights up, but it goes out if the car is positioned at a forward slope, because the volume of oil in this case flows forward and is sucked in through the crack.

So, this problem is real, unlike oil foaming. Tuning shops for these Subaru motors offer reinforced oil intakes, which still maintain normal oil suction under severe side overloads, when the oil in the sump pours from the “umbrella”.

Fourth connecting rod liner scuffing problems

This situation takes place on EJ25 motors, and scuffing can occur on the liners of the second and third connecting rod. Again, this is not a matter of engine design, but of poor and untimely maintenance – low oil level leads to high friction due to lack of oil fluid in the system, and therefore scoring.

In addition to lack of sufficient oil level, the problem can arise from the quality of the fluid itself. Poor quality manufacturer, incorrect viscosity, liquefaction of the oil over time. If you do not spare money for service and maintenance of the motor, EJ25 will please the owner, even if its mileage has already reached the mark of 500 thousand kilometers.

Oil burn

Problems of increased oil consumption really cause problems to fans and owners of Subaru brand. On this kind of motor, you should check the oil level regularly, maybe even every day. It is important to note that the car should be parked on a level surface for the check to be accurate. The very problem of increased consumption can only occur if the motor is not well maintained. Delaying oil changes, using poor quality oil, experimenting with viscosity – all this will sooner or later lead to the laying of piston rings. Well, and, of course, do not forget that leaks can occur due to the lack of tightness of the cylinder-head gasket, which we talked about above.

Tuning the engine Subaru EJ25

Just like with the 2-liter EJ20, there is no point in tuning the atmospheric EJ25, sell it and buy EJ255 or EJ257, in this series only they are worth refining.
You can add about 30-40 hp with a normal chip with a rolling exhaust. To get more power on EJ255 you need some modifications, which, in general, do not differ from those recommended for building fast EJ205, but the turbine is better to use from STI – IHI VF48. It will be possible to get 300+ hp on this config.

Making EJ257 go faster will help configuration on TD05-18G turbo, as in the description for tuning EJ207. This will produce 350+ hp. Of course, you can take 400+ hp off as well, but you need much more serious spending on tweaks.

ENGINE RATING: 4