Angry Kitchen Appliances


 Information about crankcase ventilation and oil sludge for the engines B205 and B235

Denna sida finns även på svenska.

  1. Background
  2. Prototype
  3. Model years 1998 to 2003
  4. Modification 1, October 1999
  5. Modification 2, May 2002
  6. Modification 3, November 2003
  7. Modification 5, March/April? 2005
  8. Model year 2004
  9. Modification 4, November 2004
  10. Model year 2005
  11. Tips
  12. Notice
  13. Links

 Background

 Crankcase Ventilation?

In an ordinary internal combustion engine (petrol) an over pressure is created in the crankcase of the engine. The over pressure is the result of combustion gasses leaking past piston rings (down into the crankcase) and past valve guides/valve seals (up into the valve cover). The over pressure in the engine results in problems, e.g. oil leakage, and must be ventilated out of the engine. Before modern environmental laws the crankcase gasses were ventilated directly to the air, modern engines must handle the ventilation in a much more environmental friendly way. The most common method is to route the gasses into the engine to be burnt.

 Crankcase Ventilation in the 9-5

Saabs four cylinder petrol enginesB205 and B235 are low friction engines. This means that Saab, amongst other things, used weaker piston rings to reduce the friction with the cylinder walls. The weaker pistong rings, however, allows more combustion gasses to escape into the crankcase. This increases the crankcase pressure and increases demands on the crankcase ventilation system. The crankcase ventilation system has, unfortunetely, not been able to handle the demands.

 Risks with bad crankcase ventilation

A badly working crankcase ventilation system can in some cases, such as frequently driving short distances or frequent city driving, cause many problems.

An engine oil that is exposed to stress due to bad crankcase ventilation can, if it is not replaced in time, result in a broken timing chain or a clogged up engine. The combination of bad crankcase ventilation, short driving distances, cold climate, long oil change intervals (20000km is way too long) and cheap oil is a disaster for the engine.

 Why does this page exists?

This web page tries to explain how the crankcase ventilation system works, and how it does not work, and show the changes that gave been done since the 95 was introduced.

 Prototype

To compensate for the increased crankcase pressure Saab dezigned a crankcase ventilation system that was different than the system used in the earlier engines.

The crankcase gasses are evacuated from the valve cover through hose A to a oil trap that condenses the oil mist and returns the oil to the oil pan. The crankcase gasses, now without oil, is routed through hose B to a pressure regulator and valve. The pressure regulator tries to keep the pressure in the crankcase at a suitable level. A control signal from the Trionic engine management system determines if hose/pipe C or hose D is used to evacuate the crankcase gasses. Hose/pipe C is used when the engine is loaded and a low pressure is preset at the inlet side of the turbo. Hose D is used when the engine is idle and a low pressure is is preset in the throttle housing.

Unfortunately this system could not be used as OBD2, in cars for the US market, has to supervise electrically controlled functions, in this case the Trionic controlled pressure regulator/valve. It was not feasible to do this supervision and this design was scrapped just before model year 1998 was introduced.

[Prototype] (8kB)

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 Model years 1998 to 2003

As the system controlled by Trionic could not be used a system resembling the system used on earlier engines was introduced. However, the oil trap was still used.

The crankcase ventilation has two states.

 Light engine load

Ar light engine load, idle or engine brake, a low pressure is available at the throttle hosing. This low pressure draws the crankcase gasses from the valve cover through hose C. The evacuated gasses consists of crankcase gasses and air drawn from the inlet side of the turbo through hose B, oil trap and hose A. A restriction in the oil trap (4mm hole where hose B is attached) acts as a crude regulation of the pressure in the crankcase. A check valve on hose C prevents pressurization of the crankcase when a high pressure is present at the throttle hosing, e.g. when the turbo is creating pressure.

 High engine load

At high engine load the venturi effect is used to create a low pressure at the connection of hose B at the turbo inlet. This low pressure draws the crankcase gasses from the valve cover through hose A to the oil trap that condesnes the oil mist and returns the oil to the oil pan. The crankcase gasses, now without oil, is routed through hose B to the inlet side of the turbo.

 Problems

This design has problems, i.e. are gasses evacuated through hose C without using the oil trap. This draws oil into the throttle housing causing a check engine state and often a new throttle housing must be installed to correct the problem.

[1998 - 2003] (7kB)

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 Modification 1

About October 1999.

Quite early it was shown that the crankcase ventilation did not work properly. The check valve on hose C couldn't take the abuse and often failed. On earlier engines the same valve performed without problems, but on the Trionic 7 engines with its drive-by-wire throttle the valve failed due to the quick pressure changes caused by the quick throttle position corrections done by Trionic 7. The check vale is replaced by a larger check valve.

This modification should have been done on all cars with the old check valve. Campaign plate should be marked in square B5.

[Modification 1] (7kB)

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 Modification 2

About May 2002.

More problems. Many cars produces blue smoke clouds at cold start and the crankcase ventilation is part of the problem. Many cars is running with more or less non-existing crankcase ventilation.

Some modifications are done to improve the crankcase ventilation. The connection for hose C at the valve cover is drilled to 3mm and the restriction in the connection for hose B at the oil trap is drilled from 4mm to 6.5mm. As an extra modification the larger oil trap from the B235R (Aero) engine could be mounted.

This modification apperars to be done only when the owner complains about the earlier described problems. No markings on the campaign plate.

[Modification 2] (9kB)

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 Modification 3

About November 2003.

Once again more modifications are needed.

More modifications aiming to improve the crankcase ventilation system is done. The connection for hose C at the valve cover is blocked and hose C is instead conencted to a nipple screwed into the oil filler neck. The restriction in the connection for hose B on the oil trap is drilled from 4mm (or 6.5mm) to 10mm and a check valve with a restriction is mounted on hose B. The check valve with a restriction replaces the restriction in the oil trap and is free flowing in the direction from the oil trap to the inlet side of the turbo and a restriction for air in the opposite direction.

Saab article nummer 5962428 is a kit with all parts needed for modification 3.

Even this design has its problems, e.g. hose C is still used to evacuate gasses without using the oil trap. This is very likely the reason why som many owners complain about high oil consumption after this modification. Tests on my 95 shows that 1ml of oil for each 10km (i.e. 1 liter of oil for 10000km) is sucked out of the engine through hose C. This matches what is reported for other engines.

The ventilation through hose C is now so strong that it, on some engines, sucks air past the gasket under the yellow lid. When the weather is humid this results in moist air entering the oil filler neck and a yellow-white oil-water-mix is created under the yellow lid.

This modification apperars to be done only when the owner complains about the earlier described problems. No markings on the campaign plate.

The modification kit was withdrawn by Saab in December 2004 and this modification should no longer be done. This is probably because of the increase in oil consumption caused by this modification.

[Modification 3] (10kB)

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 Modification 5

About Mars/April 2005.

Rumors about yet another modification.

 Model year 2004

It seems that Saab intended to fix the problem for good with model year 2004. Many changes were done, unfortunately many of the modifications are not reasonable to make on already manufactured engines.

A new oil trap is introduced. It evacuates crankcase gasses from the valve cover through hose A and directly from the crankcase through connection B in the engine block. The gasses are then routed to the turbo inlet through hose C and to the throttle housing through hose D. Hose D is larger than the corresponding hose in the earlier design and has a larger check valve.

The changes required a new engine block, new valve cover, new throttle housing, new oil trap, new check valve and new hoses.

[2004] (12kB)

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 Modification 4

About November 2004.

Model year 2004 cars is upgraded with a new oil trap from model year 2005 cars. The intention is to reduce the oil consumption.

 Model year 2005

Model year 2005 seems to have the same crankcase ventilation system as model year 2004, except that a check valve with a restriction has been added to hose C, i.e. just as modification 3 for earlier model years, plus a new oil trap.

 Tips

To reduce the risk that the crankcase ventilation gets so bad that the engine is risking damage you should modify the crankcase ventilation following Saabs instructions for modification 2 and then inspect the crankcase ventilation regularily.

Use fully synthetic engine oil of good quality and preferably change it more often than the regular interval. Saab recommends shorter oild change intervals if the car is driven in city traffic or is driver short distances in cold climate. It could be enough with one skipped oil change in combination with bad crankcase ventilation to create so much damage that a engine renovation, or a new engine, is needed.

[1998 - 2003] (7kB)

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 Notice

The information on this page is a collection of publicly available information. Details are, for example, taken from workshop manuals, changes done to my own car and from information posted on the Internet.

 Links

 


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Last modified 2005-08-05 23:34:26 (built 2013-01-22 19:56:21).
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