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1999-2009 [Subscribe to Daily Digest] |
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The whole PCV topic seems to have died down around here lately, but in lieu of Saab coming up with yet another modification for the older cars, I’ve been thinking about the flaws in the system and trying to figure out how to solve the problems. There is a website, a link to which I cannot post for some reason, that has a very good chronology of the various evolutions of the PCV system on the 9-5 2.3.
Based on the different modifications that have been tried, it seems that the problem of insufficient ventilation can be put down to a few possibilities:
- Plugged or split hoses
- Bad check valves
- Design flaw causing insufficient ventilation of the lower part of the engine block
- Design flaw of PCV hose bypassing oil trap
The first two are simple cases of questionable materials being used – hard steel lines would be a much better choice for all the PCV lines. Plugged lines could be worst of all, as this could easily lead to the fumes being pushed back into the oil pan via the oil return hose at the bottom of the oil trap. The check valves have already been redesigned once, but even the new units fail (I had a failed one on my car when I got it). Obviously, all owners should check their cars to make sure the system is working properly.
The design flaws are the real problem. Tracing the history of the modifications Saab has tried suggests that there are two separate problems. The insufficient ventilation of the lower crankcase could contribute to sludging and is probably the most serious flaw. The small PCV hose that runs from the valve cover to the throttle body does not go through the oil trap and likely is the source of many of the oil smoke on startup problems, and perhaps throttle body failures as well. In the original position (from the valve cover) the small line draws fumes only when the engine is at idle or very low RPM – this may exacerbate the problem on cars that see a lot of stop-and-go driving.
If one looks at the MY 2004 and 2005 PCV arrangements it can be seen that Saab has altered the design to address these issues. One major difference is the addition of a vent in the crankcase area that feeds into the oil trap – this is something that cannot be added to cars without major work.
What I’ve been trying to do is figure out a way to correct the design flaws on the earlier cars. Modification 3, now discontinued due to high oil consumption, suggests a potential solution. This modification used a nipple in the oil filler neck to draw fumes out of the lower crankcase. The oil consumption problem likely got worse because these fumes went straight to the throttle body. It seems to me that by redirecting these fumes to the oil trap before consumption could be dramatically reduced while still achieving the aim of increasing the ventilation of the crankcase. This would require the nipple be added to the oil filler tube, and two similar nipples added to the top of the oil trap. A hose feeding from the filler tube to the oil trap would be added, and the existing hose containing the check valve would be rerouted to go from the oil trap to the throttle body. This should (in theory, at least) allow the crankcase to be well ventilated and direct all fumes through the oil trap before being drawn into the intake tract.
I haven’t tried any of this yet. My car is a 99 with 103k miles and the original unmodified PCV system. When I got the car I replaced a split valve cover-to-oil trap hose and a bad check valve. The system is working as designed, and the car has no sludge issues and no oil in the throttle body. Nonetheless, there is clearly a possibility to come up with a better system. What I’m suggesting is merely one possibility, one which I think will address the shortcomings. When I get ambitious enough, I will rip in and try it – at worst I need a new oil trap. I am very interested in hearing comments (good, bad, or indifferent) from people about these ideas – there may well be something important that I overlooked, or some fundamental flaw in my logic. Please don’t hesitate to tell me if you see something wrong in the above.
posted by 68.199.129...
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