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Oil, sludge, strainers and breather systems in 4 cylinder SAAB petrol engines: a study

Related articles (in the workshop procedures section):

Dropping the 9-5 sump
Re-meshing the oil pick up strainer


1.0 Introduction

This study resulted after a need was identified to answer a growing number of queries concerning the longevity of SAAB power units, which seemed to be suffering from abnormally high rates of premature failure on the road. The aim is to explore the phenomenon, defining its scope, identifying the nature of the problem and understanding underlying causes. with a view to making conclusions and recommendations.

1.1 Background

During the course of the 1990s, a small number of SAAB 9000 engine problems occurred that were wholly attributable to blocked sump strainers. The photograph (below) shows a piston from a car that went 17000 miles without an oil change. Sludge blocked the sump strainer and crucially a piston cooling jet causing serious damage.

Ostensibly, lack of maintenance and neglect were cited as the drivers for this unwelcome development. Later, 9-5 engines started to exhibit abnormally high failure rates. In December 1999, SAAB issued dealers with Service Bulletin 210-1991 that advised technicians to carry out a simple test when carrying out oil changes on all 4 cylinder petrol engined cars. The test involved probing the sump with welding wire inserted through the drain hole and scraping first the base of the sump, then the sump strainer before withdrawing the wire. If carbonised particles were found, it was recommended that the sump should removed immediately and the strainer cleaner or replaced as necessary. In the two years since the 9-5's introduction, a worrying trend had been observed whereby cars with higher than average mileages were experiencing oil starvation problems within the engines.

1.2 Scope and nature of the problem

With a relatively small number of problems with the 9000, followed by greater frequency of problems with 9-5 engines, a trend emerged. Six cylinder cars were not suffering - problems with the oil circuit were confined entirely to four cylinder models.

SAAB engineers identified the problem quickly as a process they dubbed 'sludging' whereby oil was breaking down or degrading into small, mostly soft carbon particles. Once in the lubrication circuit, the particles would end up at the sump strainer, where they would accumulate, eventually restricting the supply of oil to the oil pump. Some of the affected engines started to make a strange humming or whining noise upon start up - a sure tell-tale sign of problems with oil supply. Oil starvation on turbo-charged engines was bound to have serious consequences and although damage to crankshafts and turbo chargers was most common, another scenario involved damage to the cylinder bore when pistons broke up or connecting rods came through the side of the cylinder block, effectively destroying the engine. Research carried out by engineers concluded that excessively long oil change intervals or a combination of operating the engines in cold environments with repeated stop-start driving could exacerbate the condition.

1.3 Sludging and its causes explained

One common question was why this problem had not affected the 9000 range so much. To the casual observer, the engines in the 9-5 looks very similar to the 9000 but there are very significant differences. Everything above the cylinder head gasket is completely different, from the intake and exhaust manifolds to the cylinder head itself. Within the block, hidden from view, the pistons and connecting rods in the B205 & B235 are of a different design to the 9000. The redesigned pistons and rings in effect reduced friction inside the engine but this increased crankcase pressures. This wasn't so much penny pinching so much as an expensive retool necessary to operate an efficient breather system to ensure compliance with current and future emissions legislation in all existing and potential world markets. Add different turbo-chargers and a new management system to end up with a thorough revision of the old B204/234 engines.

The service intervals crucially, were also revised from 6,000 to 12,000 miles. Although the Aero service schedule specifies fully synthetic oil, there appeared to be no such stipulation for lesser models - even though every new SAAB had left the factory filled with fully synthetic oil since 2000. Some independent specialists and a small number of dealers continued as before, putting semi-synthetic oil in 9-5 engines

Revised pistons and rings in the B205/B235 engine tested the breather system to its limit, especially when the cars were used in cold conditions for short runs and the engines never reached full operating temperature. Excessive crankcase pressures caused the oil to degrade through contamination by some of the by products of combustion which also attacked the rubber components of the breather system itself. The rubber hoses making up the breather circuit can break down so that they feel 'squidgy'. These soft particles were augmented by harder particles as the depleted and oxidised oil literally fried in the turbo charger. A number of serious engine failures have occurred after owners have failed to heed the tell-tale smell of oil fumes inside the cabin before substantial quantities of oil have been thrown down the back of the engine when pipes have not only collapsed but split in two.

Extensive conversations by the author with experienced parts and service staff revealed that although blocked strainers were the root cause of engine failures, only staff with many years experience noticed that the actual mesh in strainers fitted to engines made after 1993 was finer than that used previously in 9000s, where lubrication failures were virtually unheard of. Further investigation confirmed that the type of mesh used changed from having 20 holes per inch (20 mesh) to one having 30 holes per inch. This change had not gone unnoticed by others and in the USA, a retired aircraft engineer called Mr Shultz changed the mesh within the strainer back to 20 mesh, after noting that aircraft engines on which he had many years experience ran with this type of strainer mesh. Shultz concluded that wider holes in the mesh would allow the passage of larger particles into the oil pump, where the case hardened gears would mince them before they were trapped in the oil filter. So long as very regular oil changes were carried out using fully synthetic oil, there would not be a problem.

Sludging has been a popular subject on bulletin boards around the world and not just SAAB engines have suffered. Recently, it came to light that numbers of Audi TT engine failures had occurred and it was no coincidence that usage of semi-synthetic oil and extended service intervals were cited as some of the root causes. Using popular search engine Google with the search string 'oil sludging' quickly reveals that some Audi, Lexus, Toyota and VW vehicles are also affected.

Many independent SAAB specialists offer what has become known as 'the sump service': an operation that involves draining the oil, dropping the sump and cleaning the strainer. Some have formed the opinion that just one oil change using semi-synthetic oil is quite enough is to start the formation of sludge. Others point out that the so called sump service doesn't go far enough and that a better approach is to remove, drain and clean the oil cooler at the same time. The justification for this is simple: when the oil is drained something like a litre of the old oil and presumably some sludge remains in the cooler. Readers should be advised that removing the oil cooler on a 9-5 is both fiddly and potentially messy.

Part of the problem is that the general public perceive semi-synthetic oil to be 'just as good' because the word semi is equated with half and it has been generally assumed that semi-synthetic oil has a composition of 50% synthetic polymer. This is a misconception because in order to qualify as semi-synthetic oil, the composition must be a minimum of just 5% synthetic polymer and only the very best will be 40%! With spirited driving, it is quite possible to get turbo-chargers glowing cherry red - nothing but the very best oil will do.

2.0 The maker's response to the problem

As stated previously, SAAB acted on the problem as long ago as 1999 by issuing a bulletin advising dealers to check sumps and strainers during oil changes. This was followed up by changes to the recommended lubricant specification from semi-synthetic to fully synthetic engine oil. In late 1999, a modification to the breather system that entailed changing a check valve became available.

By 2002, it became apparent that more work on the breather system was required and a bulletin outlining work to increase the flow of combustion by products within the crankcase circuit was issued to dealers before a third effort to combat problems was announced. Unfortunately, fitting the kit of modified parts was not the complete solution, for some owners started to experience high oil consumption. A wholesale revision of the breather system followed in a more radical approach that involved the design of a new cylinder block for model year 2003 cars - these engines may be distinguished by their silver alloy (as opposed to black) cam box covers. Of course, fitting a whole new cylinder block to older cars was not cost effective, so SAAB came up with another breather modification for older cars. The kit is still available as OE part 55561200. The author has fitted this kit to a number of cars.

Sludging has been such a problem that SAAB offered an 8 year unlimited mileage warranty on the engines and in many cases, fitted replacement engines at no cost to the owners of affected vehicles - so long as they could demonstrate a qualifying service history, backed up by invoices to prove that maintenance had not been skimped.

3.0 Findings reviewed

The evidence available suggests that sludging is an issue that affects mostly (but not exclusively) SAAB 4 cylinder turbo-charged petrol engines produced after 1998, specifically the B205 and B235, as fitted to the 9-3 and 9-5. Excessive mileages between services, coupled with the use of semi-synthetic oil and poorly maintained breather systems and operation on short runs in cold climates are all major factors that contribute to the formation of sludge which WILL damage engines by preventing lubrication of major components by blocking the oil pick up strainer.

With the benefit of hindsight and no small amount of research, it is argued that the root causes of failures are now well known and that proper, regular maintenance will greatly reduce the incidence of future failures.

4.0 Recommendations

Clearly, the use of fully synthetic oil, changed more frequently than the original schedule of 10,000 miles (6,000 mile intervals are recommended) is essential. Cars with unknown histories or which might have been run just once on semi-synthetic oil should have the sumps dropped and the strainers cleaned/replaced promptly. Owners need to be aware that the sump strainer is just part of the lubrication circuit - another seriously good idea is to drain and clean the oil cooler. The breather system in particular needs to be checked regularly for split or collapsing hoses and it is a good investment to switch to the latest modification (SAAB OE part 55561200) if this has not been fitted already on cars made before 2003. In service, cars which develop a humming or whining sound after start up and at tickover need workshop attention without delay, as do cars in which a smell of oil fumes can be detected in the cabin. We have discovered that on some cars, even with new breather systems, there is a smell of oil - in which case, the oil dipstick and seal should be renewed.

5.0 Acknowledgements

The author acknowledges the considerable contribution made towards this report by fellow enthusiasts both in the UK and abroad. Some very useful advice and comment has been supplied freely by many independent SAAB specialists (and one VW/Audi technician) too. Surprisingly, there were mixed results when requests for information were made within the Petroleum industry. At a local level, a major supplier of oils and fuel (who asked not to be named) provided invaluable insight but approaches to both Mobil, Castrol and Valvolene were all ignored. The author believes that there is little point in spending thousands of pounds on a corporate web site if staff who are paid to respond to customer queries cannot be bothered to do so. If companies didn't wish to respond for legal reasons, it would have been nice to have received even a couple of lines in an e-mail to say so. As it stands, many readers will smile in the certain knowledge of the outcome that would have transpired had any of these people worked for Sir Alan Sugar...


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