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The question is whether the engine is now very hard on engine oils, or if the problem is oil neglect by prior owners or folks who lease (some do not give a damm).
It is apparent that one can neglect oil and build up stable sludge in an engine, and this can become mobile later... a time bomb. Synthetic oil can soften the mess that can then plug the oil intake screen that some have stated has an insanely fine screen. Yes the pump is protected from larger solids, but the motor then fails. Were the oil pick up screens on prior versions of this engine fine or course? I think that the screen should be courser and let the disposable oil filter do the job.
New engines have the piston rings moved much closer to the piston tops, which reduced HC emissions. But this also makes these rings run hotter. So perhaps this is leading to some oil oxidation that did not occur years ago.
Neglected oil changes are probably often with cheap oil.... human nature. After the oil addatives are depleated the oil chemisty goes very bad. the oil can polymerize to form a plastic material. Wear metals that accumulate and are not drained off, build up to high levels. These metals act as catalysts to promote the polymerization. Japan dryer is a solvent with metal compounds added, that is used to accelerate the drying of oil paints and oil finishes. Paint drying is a loss of solvent, but mostly a process of polymerization of the oils in the paint. So that is an example of the effect of metals on such processes. (laquers are different and they simply loose their solvent to become solid) Japan dryers contain lead, among other things nasty. So if lead promotes polymerizatiom, then perhaps acclerated wear of shell bearings is releasing lead and other metals from the babbit that accelerate polymerization.
And neglected oil can lead to sticking piston rings, which increases the blowby gases. The HC and NOX contamination then further damages the oil. The NOX oxidizes the oil which is one of the processes of polymerization.
And note that when oil is neglected and the oil is degraded, that this, and the accumulating wear metals in circulation, can lead to rapid increases in metal wear rates, and the wear processes may spiral out of control. And as the oil pickup screen gets restrictive, oil pump volumes go down and some areas of the engine may wear faster yet, and oil cooling degrades and oil temperatures increase which increases polymerization reaction rates.
Modern oils are very different from old oils from years ago. Perhaps these oils react drastically to depletion of addatives compared to the simpler oils. The viscosity index improvers might be part of this or the primary actors, but who knows.
So we know that these engines are polymer reactors when things go wrong with the oil. And setting years of accumulated sludge free leads to disaster. So I feel the need to state that any used Saab needs to have the valve cover removed to eval slude. That has been suggested before. I don't know if deposits always show up there when the crankcase is a mess. Perhaps others can make some definate statement about that. And an engine perhaps needs the VC removed for inspection before switching to synthetic oil.
So why did Saab switch to semi then full synthetic oil? Perhaps in part to have an oil that is more resistant to high temperatures and oxidation. Yes there are other reasons, longer change intervals and economic an enviromental impacts, but they know that engines are dying from sludge. A new Saab engine on M1 0W40 or 5W40 is probably never going to suffer from these problems if the oil is changed properly.
Piston blow by gasses are very hard on engine oil. We have seen one or two reports where newish engines needed new piston rings. If some engines have a lot of blowby gases, that might overwhelm the oil and the longer oil change intervals might then be fatal. So perhaps these longer oil change intervals create a situation where there is no margin for error, or no safely factor.
So thats the way that I see it. Not much help. I would close in stating that all used Saab engines need to examined carefully. And while the VC is off, the head bolts are right there and these can be test torqued very easily. And Saab engines are not the only ones with such problems.
posted by 66.142.222...
, Fri, 21 Jan 2005 15:57:30
, Thu, 20 Jan 2005 19:59:23
, Wed, 19 Jan 2005 09:39:35, Wed, 19 Jan 2005 13:04:34
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