1994-2002 [Subscribe to Daily Digest] |
As for 'coking'.
When oil breaks down it can create a hard carbon deposit. This used to be a problem where oil coked in the turbo charger bearings. But with water cooled turbo charger bearing housings, this does not occur anymore. But there is still a risk with pistons where oil and partial combustion byproducts coke in the piston ring lands. The rings can get stuck and blow by increases making the degree of these deposits worse. And compression goes down and oil consumption goes up, again making the problem worse.
For various reasons, the distance from the top ring land to the piston top has been decreased. This provides several benefits, but the top ring land in these modern designs is running much hotter. Some of the evolution of motor oil standards has been to address this hot spot. A true full synthetic will provide the best protection from coking in the rings. The heat load on these pistons is greatly increased when on boost. So for those who have increased boost pressures, the needs are greater.
The biggest problem and almost univeral problem that I have seen in engine rebuilds is stuck piston rings. So for me this is a critical issue.
Mobil One is a true synthetic oil. However, Castrol Syntec is a highly hydrocracked dyno oil, a group III oil that is not as good. Note that they state that it is synthetic and charge the same as Mobil One for modified dyno base stock. There are also other good fully syntheic oils in the market place.
The need for better oils is often not known by the engine designers until they get to appreciate what is happening in the engines after years of real service. And oils are evolved over time to meet new requirements. Take the VW TDI diesel engine. It is largely unchanged in several years. But the oil requirements went from dyno CD to better dyno diesel specs then too 10W30 synthetic diesel specs then to synthetic 5W40 CH-4. One of the issues these changes is addressing is ring coking and cam lobe wear. As diesels warm up much more slowly then gassers, the 5W was spec'd to get good oil flow in cold engines during this extended warm up time. The cam lobe pressures in diesels can be higher in diesels because of the mechanical loads of the injector pump. Then there is the issue of soot loads in the diesel oils. That presents a whole new story of issues and oil formulation evolution.
I don't expect that Saab spec's syntheic blend because they did not observe problems with dyno oil. This would address ring coking. If cam lobe wear was an issue, a full syntheic would probably be required. I an troubled with the stories of problems with pumps and chains in the 2.3 NA engines. This is a lube performance problem. Why the 2.3 L enginges... well perhaps these folks as a group are less inclined to spend more money on better oils, but one has to contemplate the fact that the 2.0 turbo has a larger capacity oil pump. So if there is a marginal lube situation with the 2.3NA engine, then all I can see is a great need for a superior engine oil.
I will be trying out a super strong magnetic oil drain plug. Perhaps it will be a good idea for the 2.3's that seem to be sheading chain bits that wreck the pump and other things. Perhaps the chains are the archillies heal of the Saab engines. I expect that the two engines are running the same gears and sprockets etc. All the more reason for panoid compulsions for syntheic oil!
posted by 208.24.17...
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