BMW E38
Timm's The BMW M60 M62 M62TUB and N62TUB Engine
Crankcase Ventilation - OSV and PCV
Above is the PCV or Pressure Control Valve, it is fitted to the rear of the Inlet Manifold
The picture above shows how the system is connected, the oil separator valve (OSV) is housed in the crankcase. Blow-by gasses mixed with
oil vapour enter the OSV under vacuum provided by the inlet manifold, the cyclone action of the OSV spins oil from the vapour, the oil drains
back to the sump. The clear gasses pass through the vent tube, through the PCV and into the manifold.
The PCV at the rear of the crankcase contains a pressure control valve that is set to provide a slight vacuum at the vent tube of 10-15
millibars (equivalent to 6" of water). This regulation of vacuum is important, to deep a vacuum and oil will be drawn from the crankcase, too
little and the cyclone action will not function efficiently.
Below are photographs of the PCV and OSV fitted to the M62TUB engine:
The OSV can be seen here below the cam drives of Bank 2, the metal pipe at the bottom returns the oil to the sump
Above is an unusual view, the rear of the M60 showing the PCV (red outline) and vent pipe (blue outline) on the rear of the manifold.
Problems associated with the crankcase ventilation system
The rear cover has been removed on this PCV, revealing burnt oil and a brittle diaphragm
The PCV above is pretty typical, the diaphragm is brittle, probably split around the rim, and the cavity is full of burnt oil. The spring in the
middle is what sets the crankcase pressure, the inlet manifold vacuum pulls the diaphragm towards the spring, as it moves forward it
restricts the central pipe which leads to the manifold, and that reduces the vacuum at the diaphragm. The vacuum on the diaphragm and
spring pressure from the other direction regulates the crankcase pressure to 10-15 millibar.
If you have any of the problems below, read on!
•
High oil consumption
•
Blue smoke on cold starts
•
Blue smoke under acceleration
•
Poor idle
•
Misfires
•
Error Codes P0170, P0173, P0300, P1174, P1175, P1340
•
Howling noises from the rear of the engine
Above is the OSV or Oil Separator Valve which is housed behind Bank 2's upper timing chain cover
The N62 engines have the OSV built into the valve covers
Above, there are two OSV’s and two PCV’s on the N62 engine as fitted to the E63/E64/E65. Note: The Oil
Separator Valve on the N series V8's is built into the cover above
Problems associated with the crankcase ventilation system
•
High oil consumption
•
Blue smoke on cold starts
•
Blue smoke under acceleration
•
Poor idle
•
Misfires
•
Error Codes P0170, P0173, P0300, P1174, P1175, P1340
•
Howling noises from the rear of the engine
•
Poor pickup under light acceleration (N62)
The list of problems above are often caused by a faulty crankcase ventilation system, and others. The weak spot is the PCV valve which is
fitted to the rear of the inlet manifold. Below is another failed one:
Two failed PCV’s on my N62TUB48
Yes, even on the new range of BMW engines the PCV’s are still getting gummed-up, torn and frizzled. This caused a poor pick-up
under light acceleration. Symptoms are slightly different on the ‘N’ range of engines as the throttle butterfly is normally fully open
and the aspiration is controlled by the Valvetronic valve lift - that means less manifold vacuum
The PCV fails in a number of ways
The diaphragm cracks and disintegrates - this allows un-metered air into the manifold. This fault leads to a number of problems,
poor idle, multiple misfires, adaptations reached limits, pre-cat O2 errors.
The diaphragm sticks to the rear cover - this increases crankcase vacuum and pulls oil into the manifold through the oil-separator
valve due to the disturbance of cyclonic action This is the cause of the plumes of smoke that scare most people to death. It also
coats the inside of the inlet manifold with oil that slops around and produces more smoke when cornering or braking.
The diaphragm sticks to the central manifold pipe or the vent tubes are blocked with old oil - this causes excess crankcase
pressure This fault is not immediately obvious, but is often the cause of oil leaks at the crankshaft front and rear seals. It also
increases the oil leaks from the rocker covers.
Finally, regarding the crankcase ventilation system:
Should removing the dipstick produce a gurgling noise?
The answer is it depends on the amount and viscosity of the oil in the sump. The vacuum in the crankcase should be 10-15 millibars
(up to 27 millibars for the N62xxx engines), so air will be drawn into the crankcase via the dipstick tube, whether it makes a noise is
dependant on the oil level reaching the end of the tube, viscosity and temperature of the oil.
Should removing the oil filler cap change the idle speed?
Yes, it should as un-metered air is reaching the inlet manifold, you will also get a good spray of oil from the timing chain!
Should it be difficult to remove the oil filler cap with the engine running? It needs around a 8oz pull to remove the cap when
the internal vacuum is at the correct 10-15 millibars.
How can the PCV be tested for correct operation?
By checking the crankcase vacuum. This can be checked using a vacuum gauge at the dipstick tube, or, as BMW does, use a modified
oil cap with a pressure take-off point screwed into it. Alternatively, a really simple test can be made by using a 1-metre length of
clear tube that fits snugly in the dipstick tube, filled with a few cc's of engine oil and arranged as below:
A simple manometer made from clear tube with a few cc's of engine oil and stuck firmly in the dipstick tube
With the engine idling, the available vacuum in the crankcase should lift 6" of water - that is, a 3" drop and a 3" lift as shown above - the
weight of oil is very similar to water and you will get the same readings without the possibility of getting water in the engine. If there is no
vacuum, then the oil will stay level, if the vacuum is too high the oil may be drawn from the tube. A reading between 4" and 8" is acceptable.
If the reading is outside these readings, or outside 10-15 millibars as read on a vacuum gauge, then it is most likely that the PCV has failed.
A very low vacuum may indicate a vacuum leak, but the leak would have to be reasonably large to defeat a correctly working ventilation
system.
Replacement of the PCV is covered here
Differences between M60/M62/M62TUB manifold PCV system
There are subtle differences between the inlet manifold's used on the different versions of the modern BMW V8. On the M60, the PCV
releases the filtered blow-by gasses directly into the rear of the inlet manifold. This has the effect of allowing the gasses (which still contain a
small amount of oil vapour even on a fully working system) into the rear two cylinders. This can make the rear two cylinders run leaner than
the rest of the cylinders - but also receive the greater amount of oil. This doesn't usually cause much of a problem, but does slightly affect
the tick-over. Once the PCV diaphragm fails, the rear two cylinders will get all the oil and usually have the plugs fouled.
The inlet manifold on the M62 and M62TUB has an additional pipe that runs internally from the PCV to a mixing chamber at the front of the
manifold. This mixes the blow-by gasses with the incoming air from the throttle body - the intention is to ensure that all cylinders receive
their share of the gasses and the small amount of oil vapour from the PCV.
In addition to changes in the crankcase ventilation system, there have also been changes to the runners within the manifold. The runners
sweep from the central plenum of the manifold in a curve to each cylinder. The diameter of the runners have an affect on the performance of
the engine. At the most basic level, the smaller the diameter of the runners, the better the engine will perform at tick-over and at low revs,
the larger the diameter, the more air is available at full-throttle creating more power.
In particular, the diameter of the runners was reduced to increase the velocity of the air in the M62TUB manifold - this was one of
the changes to increase the torque at low-revs and to smooth the tick-over. The increased velocity allows the air in each runner to compress
rather than remain static when the inlet valves are closed, allowing a predictable charge of air into the cylinder. Where larger runners are
employed (as on the M60), the air becomes static in the runner after the inlet valve is closed, and this reduces the available charge as the
valves open leading to poor performance at tick-over and low revs. The reduction in runner diameter increased economy, power and
smoothness in the M62TUB engine.
An internal view of the inlet manifold from an E32 740i - not only large runners but horns as well - a rare find at the scrap yard
A popular modification to the M62TUB44 is to replace the original manifold with one from an E32 740i which not only has larger runners, but
also has trumpets (or horns) at the start of each runner within the plenum. The intention is to increase the power from the engine at full
throttle - and in that, it succeeds. The problem is that the only benefit is felt at full-throttle and at high revs, in all other conditions it
reduces the performance of the engine. It uses more fuel, the torque is decreased at low to medium revs, and the tick-over returns to that of
the M60 - lumpy! The lack of torque at low to medium revs reduces the acceleration of the 740i fitted with the M62TUB44 engine and the
M60B40 inlet manifold, although it does feel more powerful above 4000 RPM.
Other problems with the crankcase ventilation system
The vent pipe on the M62TUB engines can leak on the flexible joint between the pipe and the OSV connection. This can lead to the same
problems as a cracked diaphragm. If, after replacement of the PCV, the car fails to start correctly and has wild changes is revs at tick-over,
this is very often due to the failure to replace the vent pipe correctly. Often the front end of the vent pipe has failed to fit the OSV union and
is just dangling on the block.
A brief history of crankcase ventilation
The crankcase ventilation system causes a few problems - especially when it comes to the correct names for the two main parts of it!
Crankcase ventilation in the 1960's was pretty straightforward, it consisted of an oil-filler cap that was hollow with a lump of foam stuck in
it and a vent to the outside. This allowed the blow-by gasses from the crankcase (the gasses that were forced past the piston rings) to
vent to the outside rather than pressurise the crankcase, the oil vapour that is contained in these gasses was caught (to some extent) by
the foam inside the oil-filler cap.
Later advances used a similar system, but the gasses were returned to the inlet manifold after the throttle butterfly where any residual oil
vapour was burnt during normal combustion in the cylinders. One problem with this new scheme was that at high revs, with the throttle
closed (as when de-accelerating from high speed), the inlet manifold vacuum was very deep - and this pulled oil from the crankcase which
was burnt in the cylinders once the throttle was opened again. This produced plumes of blue smoke, fouled sparkplugs and would have
destroyed the catalytic converters that were destined to be fitted to all cars in the near future. A better scheme was required for BMW's
new V8's.
The BMW V8 crankcase ventilation system
The system used on the BMW V8's has two major changes to the scheme's discussed above.
•
Instead of a lump of foam to catch the oil vapours, a cyclone-separator is used (OSV)
•
To stop oil being drawn from the engine at high manifold vacuum, a pressure-control valve is used (PCV)
Here are the two main parts:
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Timm's The BMW M60 M62
M62TUB and N62TUB Engine
Crankcase Ventilation - OSV and PCV
Above is the PCV or Pressure Control Valve, it is fitted
to the rear of the Inlet Manifold
The picture above shows how the system is connected, the oil separator
valve (OSV) is housed in the crankcase. Blow-by gasses mixed with oil
vapour enter the OSV under vacuum provided by the inlet manifold, the
cyclone action of the OSV spins oil from the vapour, the oil drains back to
the sump. The clear gasses pass through the vent tube, through the PCV
and into the manifold.
The PCV at the rear of the crankcase contains a pressure control valve
that is set to provide a slight vacuum at the vent tube of 10-15 millibars
(equivalent to 6" of water). This regulation of vacuum is important, to
deep a vacuum and oil will be drawn from the crankcase, too little and the
cyclone action will not function efficiently.
Below are photographs of the PCV and OSV fitted to the M62TUB engine:
The OSV can be seen here below the cam drives of Bank 2, the metal pipe at the bottom
returns the oil to the sump
Above is an unusual view, the rear of the M60 showing the PCV (red outline) and vent pipe
(blue outline) on the rear of the manifold.
Problems associated with the crankcase ventilation system
The rear cover has been removed on this PCV, revealing burnt oil
and a brittle diaphragm
The PCV above is pretty typical, the diaphragm is brittle, probably split
around the rim, and the cavity is full of burnt oil. The spring in the middle
is what sets the crankcase pressure, the inlet manifold vacuum pulls the
diaphragm towards the spring, as it moves forward it restricts the central
pipe which leads to the manifold, and that reduces the vacuum at the
diaphragm. The vacuum on the diaphragm and spring pressure from the
other direction regulates the crankcase pressure to 10-15 millibar.
If you have any of the problems below, read on!
•
High oil consumption
•
Blue smoke on cold starts
•
Blue smoke under acceleration
•
Poor idle
•
Misfires
•
Error Codes P0170, P0173, P0300, P1174, P1175, P1340
•
Howling noises from the rear of the engine
Above is the OSV or Oil Separator Valve which is housed
behind Bank 2's upper timing chain cover
The N62 engines have the OSV built into the valve covers
Above, there are two OSV’s and two PCV’s on the N62
engine as fitted to the E63/E64/E65. Note: The Oil
Separator Valve on the N series V8's is built into the cover
above
Problems associated with the crankcase ventilation system
•
High oil consumption
•
Blue smoke on cold starts
•
Blue smoke under acceleration
•
Poor idle
•
Misfires
•
Error Codes P0170, P0173, P0300, P1174, P1175, P1340
•
Howling noises from the rear of the engine
•
Poor pickup under light acceleration (N62)
The list of problems above are often caused by a faulty crankcase
ventilation system, and others. The weak spot is the PCV valve which is
fitted to the rear of the inlet manifold. Below is another failed one:
Two failed PCV’s on my N62TUB48
Yes, even on the new range of BMW engines the PCV’s are still getting
gummed-up, torn and frizzled. This caused a poor pick-up under light
acceleration. Symptoms are slightly different on the ‘N’ range of engines
as the throttle butterfly is normally fully open and the aspiration is
controlled by the Valvetronic valve lift - that means less manifold vacuum
The PCV fails in a number of ways
The diaphragm cracks and disintegrates - this allows un-metered air
into the manifold. This fault leads to a number of problems, poor idle,
multiple misfires, adaptations reached limits, pre-cat O2 errors.
The diaphragm sticks to the rear cover - this increases crankcase
vacuum and pulls oil into the manifold through the oil-separator valve due
to the disturbance of cyclonic action This is the cause of the plumes of
smoke that scare most people to death. It also coats the inside of the inlet
manifold with oil that slops around and produces more smoke when
cornering or braking.
The diaphragm sticks to the central manifold pipe or the vent tubes
are blocked with old oil - this causes excess crankcase pressure This fault
is not immediately obvious, but is often the cause of oil leaks at the
crankshaft front and rear seals. It also increases the oil leaks from the
rocker covers.
Finally, regarding the crankcase ventilation system:
Should removing the dipstick produce a gurgling noise?
The answer is it depends on the amount and viscosity of the oil in the
sump. The vacuum in the crankcase should be 10-15 millibars (up to 27
millibars for the N62xxx engines), so air will be drawn into the crankcase
via the dipstick tube, whether it makes a noise is dependant on the oil
level reaching the end of the tube, viscosity and temperature of the oil.
Should removing the oil filler cap change the idle speed?
Yes, it should as un-metered air is reaching the inlet manifold, you will
also get a good spray of oil from the timing chain!
Should it be difficult to remove the oil filler cap with the engine
running? It needs around a 8oz pull to remove the cap when the internal
vacuum is at the correct 10-15 millibars.
How can the PCV be tested for correct operation?
By checking the crankcase vacuum. This can be checked using a vacuum
gauge at the dipstick tube, or, as BMW does, use a modified oil cap with a
pressure take-off point screwed into it. Alternatively, a really simple test
can be made by using a 1-metre length of clear tube that fits snugly in the
dipstick tube, filled with a few cc's of engine oil and arranged as below:
A simple manometer made from clear tube with a few cc's of
engine oil and stuck firmly in the dipstick tube
With the engine idling, the available vacuum in the crankcase should lift
6" of water - that is, a 3" drop and a 3" lift as shown above - the weight
of oil is very similar to water and you will get the same readings without
the possibility of getting water in the engine. If there is no vacuum, then
the oil will stay level, if the vacuum is too high the oil may be drawn
from the tube. A reading between 4" and 8" is acceptable. If the reading
is outside these readings, or outside 10-15 millibars as read on a
vacuum gauge, then it is most likely that the PCV has failed. A very low
vacuum may indicate a vacuum leak, but the leak would have to be
reasonably large to defeat a correctly working ventilation system.
Replacement of the PCV is covered here
Differences between M60/M62/M62TUB manifold PCV system
There are subtle differences between the inlet manifold's used on the
different versions of the modern BMW V8. On the M60, the PCV releases
the filtered blow-by gasses directly into the rear of the inlet manifold.
This has the effect of allowing the gasses (which still contain a small
amount of oil vapour even on a fully working system) into the rear two
cylinders. This can make the rear two cylinders run leaner than the rest
of the cylinders - but also receive the greater amount of oil. This doesn't
usually cause much of a problem, but does slightly affect the tick-over.
Once the PCV diaphragm fails, the rear two cylinders will get all the oil
and usually have the plugs fouled.
The inlet manifold on the M62 and M62TUB has an additional pipe that
runs internally from the PCV to a mixing chamber at the front of the
manifold. This mixes the blow-by gasses with the incoming air from the
throttle body - the intention is to ensure that all cylinders receive their
share of the gasses and the small amount of oil vapour from the PCV.
In addition to changes in the crankcase ventilation system, there have
also been changes to the runners within the manifold. The runners
sweep from the central plenum of the manifold in a curve to each
cylinder. The diameter of the runners have an affect on the performance
of the engine. At the most basic level, the smaller the diameter of the
runners, the better the engine will perform at tick-over and at low revs,
the larger the diameter, the more air is available at full-throttle creating
more power.
In particular, the diameter of the runners was reduced to increase
the velocity of the air in the M62TUB manifold - this was one of the
changes to increase the torque at low-revs and to smooth the tick-over.
The increased velocity allows the air in each runner to compress rather
than remain static when the inlet valves are closed, allowing a
predictable charge of air into the cylinder. Where larger runners are
employed (as on the M60), the air becomes static in the runner after the
inlet valve is closed, and this reduces the available charge as the valves
open leading to poor performance at tick-over and low revs. The
reduction in runner diameter increased economy, power and smoothness
in the M62TUB engine.
An internal view of the inlet manifold from an E32 740i - not only
large runners but horns as well - a rare find at the scrap yard
A popular modification to the M62TUB44 is to replace the original manifold
with one from an E32 740i which not only has larger runners, but also has
trumpets (or horns) at the start of each runner within the plenum. The
intention is to increase the power from the engine at full throttle - and in
that, it succeeds. The problem is that the only benefit is felt at full-throttle
and at high revs, in all other conditions it reduces the performance of the
engine. It uses more fuel, the torque is decreased at low to medium revs,
and the tick-over returns to that of the M60 - lumpy! The lack of torque at
low to medium revs reduces the acceleration of the 740i fitted with the
M62TUB44 engine and the M60B40 inlet manifold, although it does feel
more powerful above 4000 RPM.
Other problems with the crankcase ventilation system
The vent pipe on the M62TUB engines can leak on the flexible joint
between the pipe and the OSV connection. This can lead to the same
problems as a cracked diaphragm. If, after replacement of the PCV, the
car fails to start correctly and has wild changes is revs at tick-over, this is
very often due to the failure to replace the vent pipe correctly. Often the
front end of the vent pipe has failed to fit the OSV union and is just
dangling on the block.
A brief history of crankcase ventilation
The crankcase ventilation system causes a few problems - especially when
it comes to the correct names for the two main parts of it! Crankcase
ventilation in the 1960's was pretty straightforward, it consisted of an oil-
filler cap that was hollow with a lump of foam stuck in it and a vent to the
outside. This allowed the blow-by gasses from the crankcase (the gasses
that were forced past the piston rings) to vent to the outside rather than
pressurise the crankcase, the oil vapour that is contained in these gasses
was caught (to some extent) by the foam inside the oil-filler cap.
Later advances used a similar system, but the gasses were returned to
the inlet manifold after the throttle butterfly where any residual oil vapour
was burnt during normal combustion in the cylinders. One problem with
this new scheme was that at high revs, with the throttle closed (as when
de-accelerating from high speed), the inlet manifold vacuum was very
deep - and this pulled oil from the crankcase which was burnt in the
cylinders once the throttle was opened again. This produced plumes of
blue smoke, fouled sparkplugs and would have destroyed the catalytic
converters that were destined to be fitted to all cars in the near future. A
better scheme was required for BMW's new V8's.
The BMW V8 crankcase ventilation system
The system used on the BMW V8's has two major changes to the
scheme's discussed above.
•
Instead of a lump of foam to catch the oil vapours, a cyclone-
separator is used (OSV)
•
To stop oil being drawn from the engine at high manifold vacuum, a
pressure-control valve is used (PCV)
Here are the two main parts:
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