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, Fri, 11 Feb 2005 08:52:13
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So they may have a technical position, but now the GM bean counters and lawyers may have to review all of the implications. The layers and others doing damage control may have some valid reasons to control information. These things aways exist... sucks but true.
I still expect that the 'technical postion' is to fix only what breaks and to make changes to the PCV to accomodate excess blow by gasses. The blow by gasses are a more related to a root problem that has not been defined so far and making a higher capacity PCV system is just getting a bigger bandaid!
So the real problem is mechanical and related to compression and rings, or gasses blowing though a HG with loose head bolts. So we have years of loose head bolts and no one connects this with blow by gasses, high crankcase pressures and oil chemistry problems? Thats all too much to believe. You cannot get high PCV gas volumes without gasses leaking from [combustion chamber|intake valves|exhaust valves or|bad or incorrectly installed PCV TB orifice check valve]. If the TB orifice or tube/valve ices up, the flow can still always go out through the larger passage to upstream of the turbo compressor and downstream of the MAF.
Other source of problems: purely speculation, is exhaust gas getting up through the exhaust valve springs. There can be 30 PSI of pressure there when on 15 PSI of boost. And air blowing up through intake valve stems at 15 PSI would create crankcase pressures, but this would be clean dry air. So these gas flow rates probably exist, but might be totally insignificant and not related to a root cause.
Now siezed piston rings can lead to such problems and the rings can sieze from coked oil. And the oil can coke because of its properties or neglected oil service, where the concept of neglect relates to what is needed for the particulor oil and city/highway/short-trip profile. So that is an easy possible explaination that might be true for some?all? of the failures. Rings can sieze from coking today, as the rings have been moved closer to the piston crown which greatly increases the heat that the rings see. The oil circulation through the rings is very very small, so the oil that is there is greatly at risk if it cannot handle the heat. The true synthetic oils were developed to take the heat in jet engine turbine bearings, lesser oils would fail there. So there is a lesson in that.
And contaminated oil is prone to oxidation. With a turbo engine, the piston oil spray cooling jets and the air foamed into the oil draining from the turbo compressor only serve to increase the oxygenation compared to a N/A engine. (But we did see the early signs of oil failure in the 2.3NA engines in the NG0900's.) And the RFG-II fuels that we have today, may be creating a different oil contamination situation with blow by gas contamination compared to 10 years ago. You can smell the fuel in used engine oil today! Years ago with unleaded fuel, when using a good oil, the characteristic smell of the oil on the dipstick was like oil from the bottle, not the smell of fuel.
We had one member have a newish engine rebuilt. Compression was way off. Now there is a source of excessive blow by gasses and oil contamination. The piston rings were replaced and things seemed fine after that. So what could go wrong in the factory or parts to cause that? And the valves were reseated and lapped in for good measure. And he got a new HG as well and hand torqued head bolts.
So how to reduce blow by gasses? One thing that you can do is very gentle with the throttle until the engine is fully warmed up. Not warmth from the heater, but 9 o'clock on the temperature guage. Until you get properly warmed up, running clearances are wrong. Boost when cold starts with loose pistons. Then the pistons can warm up too fast in a cold block and the pistons can then be running a bit too tight until the block catches up. And blow by gasses created when on boost with a cold engine will tend to condense in the cold engine instead of remaining in a vapor and leaving via the PCV system.
So how to survive? Know that the head bolts are right, use M1 0W40 (must for 2004+) or M1 5W40 for --2003. Change the oil often... when depends on how you drive etc. Know that you do not have sludge prior to a switch to full synthetic. Let the engine warm up properly before getting on a heavy throttle. All of that is good advice for any engine.... but for most engines in the world, you don't have to give the head bolts a second thought.
And fouled fuel injectors can increase fuel contamination of oil, and a bad pattern that puts fuel on cylinder walls is path to death.
So yes, I have some opinions :)
, Fri, 11 Feb 2005 08:52:13
, Fri, 11 Feb 2005 14:13:29
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