Crankcase Vent Pipe

[Bob.Griffin]

I usually check the community forum a couple of times a week and it seems I learn something new every time, kudos to a wonderful source of useful A4 information. I have a late model A4 and just learned from another thread that the crankcase is vented somewhere near the front, I assumed the crankcase was sealed. Since owning the boat I have always noticed a slight smell of exhaust mixed with hot oil vapour or maybe unburnt fuel in the engine compartment. The exhaust is in great shape after I just replaced the hot section and I know all seals are good all the way back to the transom, and I know I have no fuel leaks anywhere. Now I'm wondering if this 'vented crankcase' is the culprit, and I noticed someone having connected a pipe 'from the crankcase vent tube to overboard'. Where is this vent tube? I thought I knew every inch of my engine and don't recall seeing anything obvious, but I'm still learning. Will a pipe connected to this mystery tube and maybe an exhaust blower be a good fix?

Bob

[Kurt]

Hopefully other more experienced A4 owners weigh in on this too, but I'm pretty certain that the crankcase vents through the short rubber tube that runs from the valve cover directly to the top of the flame arrestor on the carb. This tube is only about 3 or 4 inches long. If your engine doesn't have too much blowby, then this should be sufficient to keep that 'oil burnt/exhaust' smell out of the cabin. Interestingly enough, although scary, the previous owner of my boat had the blower hose (which vents overboard) connected directly to the oil fill tube - I'm assuming to control that blowby smell. Too much blowby and you can certainly purchase the kit from Indigo electronics. My motor does burn some oil and will smoke slightly from the oil fill tube area, but all I do is run the blower at all times while running the engine. I have absolutely no smell in the cabin by doing this. Probably should put some new rings in the motor or do a rebuild, but I don't know, it has 110 compression on all cylinders and runs great so I'm waiting that one out.

[Don Moyer]

Bob,

I'm attaching a guide we prepared some time ago to assist folks in dealing with blow-by from the combustion chambers which will at times emanate from the crankcase and cause undue odors in the cabin.

The factory solution to removing blow-by was the small rubber tube that extends from a fixture in the front of the valve cover down to the flame arrestor. The positive ventilation provided by the Indigo Electronics kit is a far better solution.

By the way, your contributions to the Forum are much appreciated.

Don