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Engine code

M52TUB25 engine faults.

The listing only gives the engine code.

petrol

fuel

2494 cc

displacement

125 kW (170 HP)

power

3 fault write-ups. All are important.

Before you buy

Known faults

3 important faults

critical1

M54: the DISA valve breaks and its parts can enter the engine

critical

The DISA valve is the black box on the side of the intake manifold, and it adjusts the length of the intake so that there is more torque at low revs. The shaft of the valve breaks at its base, and then the flap falls off: the pieces can get into the engine and cause major damage there. Its membrane can tear separately as well. The symptoms are juddering on acceleration and a noticeable loss of power, and the valve can also hiss loudly after the engine is switched off. The seal of the intake connection is cast into the DISA, and as it shrinks it lets false air in. Its condition can be checked with the valve removed. The flap has to turn against resistance, spring back when released, and have no play. With the vent hole at the bottom of the round valve held closed, a flap moved by hand may only spring open to 45 degrees and then has to stop. With an aftermarket DISA the experience is that the trouble is back after a year, so a repair kit or a reconditioned factory part is the better choice.

above 120,000 km

What to check

  • On acceleration watch for juddering and loss of power at low revs
  • Switch the engine off and listen for hissing from the side of the intake
  • Ask whether the DISA has been touched, and whether it is a factory, reconditioned or aftermarket part
2 more steps in the write-up

expensive2

Water pump: a worn bearing, a disintegrating impeller, overheating without warning

expensive

The impeller of the belt-driven water pump is made of plastic, and if the blades break apart, there is nothing left to circulate the coolant. The belt keeps driving the pump, but the engine gets no cooling and heats up quickly.

Show the rest

This fault is dangerous because it gives no advance sign. There is no warning signal from a disintegrating impeller, and the engine temperature runs up faster than the gauge can follow; by the time it shows, the cylinder head can already be damaged. The breaking impeller is a fault of its own on the six-cylinder built between 1992 and 1995, which is why the maker went back to a metal impeller, and then used a composite impeller in the later engines, which proved more durable. A pump with a metal impeller is still available today, as a durability replacement.

There is, however, one sign that can be caught before the failure: play developing in the shaft of the pump. That means the bearing is wearing, and because the impeller sits on this shaft, play in the shaft signals the coming end of the pump. With the belt off it can be felt by hand.

On the M54 it appears at around 120 000 and on the N62 at around 150 000 kilometres. Once the engine has overheated, the consequence stays: a warped cylinder head and a damaged gasket are no longer put right by replacing the pump.

between 120,000 and 150,000 km

What to check

  • With the belt off take hold of the water pump shaft: play means the bearing is wearing
  • Watch the temperature gauge both while driving and at a standstill: it should not climb above the usual
  • Ask when the water pump was replaced, and whether with a metal or a composite impeller
2 more steps in the write-up

Valve stem seal: blue smoke after standing, and worn valve guides with it

expensive

The valve stem seals harden from the heat and the years, and from then on oil seeps through the valve guide into the combustion chamber. There are 32 such seals on the V8, and their material was a weak choice to begin with, because it goes brittle.

Show the rest

The characteristic sign is a puff of blue smoke, and not only at a cold start: it also comes when the car has idled for a long time at a light, or when it is started after standing for a while. Oil consumption rises slowly but steadily alongside it. The valve guide often wears together with the seal, so the repair does not necessarily end with replacing the seals. The fault appears above 130 000 kilometres.

The cylinder head does not have to come off for the repair. If the workshop has a valve spring compressor that can be used with the head in place, the camshaft and the chain do not have to be disturbed either, but the job is still a long one. The shop price is between 1800 and 3000 dollars, while the parts themselves are 300 to 500 dollars by comparison.

above 130,000 km

What to check

  • Ask the seller to start it cold: a puff of blue smoke shows the seal has failed
  • If the car is waiting warmed up in advance, ask for another appointment: the fault only shows cold
  • Let it idle for a few minutes, then blip the revs: blue smoke appears here too
2 more steps in the write-up

Engine code

Factory data

Factory data

Engine family
—
Fuel
petrol
Displacement
2494 cc
Power
125 kW (170 HP)
Production
—

Generations

Which models it is fitted to

1 generations.

Information, not an expert opinion

We write the descriptions, and we put the source next to them. A person reviews them before they go out. They are still information, not a technical expert opinion.

  • A fault on the list does not mean the car you are looking at has it.
  • A fault missing from the list does not mean the model is fault-free. Write-ups are made model by model. Not all of them are done.
  • You decide whether to buy. This is no substitute for an inspection. That needs a workshop and a history check.
Details in the terms