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Original Message
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| Corroded intake manifold? |
| By Dave Shoe - 07/23/2002 12:55:21 AM; IP 63.233.226.100 |
I had one FE intake manifold which developed a leak at the exhaust gas crossover, right where it bolted to the head. It was a thin spot in the cast iron underneath the manifold which eventually allowed raw exhaust to spill into the crankcase through a pin-hole leak. The engine had a generally dry, thin black coating of oil inside the entire engine, and a couple marshmallow sized chunks of carbon near the leak at the underside of the intake. If you've recently had the valve covers off and saw that everything was coated a dryish dark gray, then this may be a possibility.
You may want to do a "leakdown" test to all the cylinders. It's much like a compression test, but offers a little extra info on the condition of each cylinder. I've never yet done one myself, so I don't know details. I do know the tester is fairly inexpensive and a valuable addition to a tool box. I'll get one eventually.
If it passes the leakdown test (which should confirm the condition of the rings), then you might start thinking about the tiny possibility there is a small exhaust leak at the intake.
Keep in mind the PCV valve operates in two modes: The "idling mode" utilizes the high manifold vacuum to hold the PCV valve partially closed to limit the flow of crankcase gasses and thus prevents drawing excessive fresh air into the oil filler cap filter. The "driving mode", where manifold vacuum is reduced, allows the PCV valve to relax and flow more crankcase air. It's a simple enough system that I don't see where it could be defective by design. A secondary function of the PCV valve while operating in both of these modes is to act as a check valve to prevent fresh fuel/air from flowing backward into the crankcase.
Shoe. |
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