The YD25 has exceptional manufacturing history, that encompasses years from 1998 to 2014 and is connected with continuous evolution of this model on the basis of its original dating from the 1998 year. The 16 year period of manufacturing shows that modification cycle of this type of engine is a necessity dictated by market mechanisms. All implemented modifications are practically justified and have functional application. The purpose of methods used by the PRSerwis is to effectively reduce consequences connected with this problematic engine and prevention required by the manufacturer, what finally results in reduction of repair and operation costs.
The YD25 did not avoid material and structural defects, what resulted in increase of prices for parts on after-markets and market of substitutes.
In the following section we will try to characterise briefly some problems and to highlight causes of failures of this specific Nissan engine model.
The main cause of the YD25 engine breakdowns is the lubrication system and selection of materials that work together.
In models manufactured from 1998 to 2004 and in cars with mileage over 100 000 km, within the connecting-rod’s bearing bushes appear first symptoms of cavitation (fig. 1) i.e. sudden change of pressure of liquid (oil) and it violent transformation into a gaz. This effect results in slow destruction of bearing bushes on third and fourth connecting-rod, what in turn results in seizure on bearing bushes of the whole engine (fig. 2) with simultaneous damage of the oil pump.
In the oil pump, its aluminium body cooperates with gear wheel that driven by shaft rotation generates oil pressure. The cavitation on bearing bushes has additional side effect: metal parts penetrate into the lubrication system and damage inside surface of the aluminium body of the pump (fig.3), what results in its gradual seizing. Insufficient output of the oil pump leads to further consequences because the main goal of lubrication system is to decrease surface friction of cooperating parts and to cool some sub-assemblies.
If the piston is insufficiently cooled by the lubrication system, its dimensions increase and it creates a counterweight to crankshaft, what results in shaft damage (fig. 4). It happens, the most frequently, on the forth crank of the shaft where oil pressure is the lowest – even the oil is missing (fig. 5) i.e. the pressure is three times lower than on the first main bearing bush. This happens because of incorrect design of channels distributing oil within engine block and shaft. After 2004 the manufacturer replaced pistons and crankshafts with ones more resistant to rise of temperature.
As it results from my experiences, the crucial part of the whole YD25 engine is the oil cooler (fig.6) placed under the oil filter base. I think that this cooler has low efficiency compared with cars of similar parameters of other makes, in which the cooler is placed outside, not on the engine. The oil filter cartridge, under manufacturer recommendation that oil must be changed every 25 000 km, also should have higher efficiency for this type of engine. However, the Nissan is not an exception here, because at competitors who manufacture similar cars this tendency can be seen also.
In 2004 design engineers implemented more efficient oil pump and this modification was a beginning of cars with longer mileages, and after 2010, of practically failure-free lubrication system.
The timing gear system as a result of problematical lubrication system did not avoid high failure rate. The most frequent failure is here excessive stretching of chains, what happens in cars in which the user changes oil every 25 000 km. The oil after such mileage is too thick to cooperate correctly with timing gear stretcher, and the thick oil increases pressure and generates higher pressure exerted by stretcher on the timing gear chains. In 2008 the manufacturer have implemented a washer (fig.7) under the stretcher that throttles oil flow to the stretcher, but engine failure rate did not decrease at all. In my opinion the cause of this is too long period between oil changes and inefficient oil filter.
The next defect of the YD25 engine is cylinder head manufactured up to year 2010 from wrong aluminium alloys, because it fails when mileage reaches about 300 000 km.
The YD25 engine was corrected only after year 2010: the collectors were changed, the camshafts were slimed down and small changes in timing gear were carried out. In this case, the time will judge if this brings some improvement. To date the customers have no reservations.
There may be noticed some another drawbacks in the YD25 engine such as: short life of turbo-charger (due to inefficient lubrication system), problems with fuel system or high prices of parts (operation), but these drawbacks may be met also in other models of cars from this market segment.
Summing up: the PRSSERWIS attempts to help to ease results of the YD25 engine failures. We have to bear in mind that what type of prevention we implement to prevent a breakdowns depends on the users themselves.
PRICELIST OF SERVICES: (net prices)
|TYPE OF SERVICE
|head replacement with a new
|repair of motor
|assembly-removal of engine