Date: Fri, 17 Jan 1997 19:21:04 -0800 From: Mike West Subject: Oil cap mayonaise and beyond Mayo, and beyond. Usual reason, so I'll know where I'm headed. :-) It was in a round-about way I pointed to the crankcase ventilation as the reason for the mayo in the filler cap. Some of you still haven't put it together so I guess that's my fault. First we look at the conditions: Someone else on the list pointed out that the gasoline molecule, when it is properly burned, gives off a lot of water. He said 7 molecules, I have no reason to even check it, I've seen 8, I think somewhere else. It's chemistry and you can check it yourself. Your piston rings are not perfect and a certain amount of gases, eg. water vapor is pumped into your engine case. Someone else pointed out that when you shut your engine down and it starts cooling, it pulls cold moist air in. You have seen the physics demo where the teacher crushes the can he heated with some water in it. Put that demo to some use here and you can see why it pulls in air. It really doesn't, as it cools it creates a partial vacuum and the air pushes in to fill said vacuum. OK, those are the conditions in any hot engine. Item: my car never has mayo, and I short trip as much as anyone. My brother does have mayo and we live under Identical conditions. The only thing different is I have the stock hoses where they are supposed to be and he doesn't. So, there is a vacuum hose going from my filler tube to the air cleaner. The filler cap is sealed stock one. In the air cleaner, there is a vacuum that runs from 0 to maybe 3 in. mercury. There is only one designed air inlet on the stock beetle. Around the crank pulley. There used to be air intake at the road tube, where the vacuum also used to be pulled but a few months ago I found out about the booty and put it on there. The road tube pulled this vacuum by the air going past it when you were moving. Either with the road tube open or closed as it is now, I still have had no mayonaise in the filler cap. Now, what happens when you have a partial vacuum on the case? Negative pressure will stop oil leaks for one thing. The air is forcing itself in so nothing else can get out. What else happens, say to water in a partial vacuum? Look at Denver, Colorado. It takes three minutes to boil a 2 minute egg. Water boils at a lower temperature in less than Sea level 14.7 air pressure. The negative pressure of Denver is pretty small in comparison to the negative pressure in your engine case. So water probably boils in your engine case at an even lower temperature. How much, I can only guess, maybe as low as 100F. So I can short trip all I like and it still boils off and carries away the water. I talked about closing off the air intake around the pulley and replacing it with intake at the valve covers. When I do that, I will also have to watch and make sure I don't let so much air in that the negative pressure is gone and it won't boil water any more. I will watch for the first sign of mayo in that cap. If I see it, I will put restrictors in the breather lines to the valve covers. I may take a look anyway before I set this up. It's not that difficult to measure the bore the crank pulley goes in and the crank pulley shaft itself and figure the cross section of area that the air has to come in. Then I drill a couple plugs that equal that and put them in the air inlet lines to the valve covers. Now, will water in oil hurt you? even if it's just a little? There is another guy who recently was looking for a cure for the case being eaten out around the oil cover plate. How do you suppose that happened? :-) Do you realize that the oils you use have an agent in them that actually allow your oil to absorb huge quantities of water? For those of you who aren't interested in modifying your engine, it isn't needed. Just put the stock air cleaner on, or one that has a vacuum hose inlet and hook that filler tube line up to it. Make sure all other holes etc. are closed off from the air. The crank pulley clearance will supply all the air it needs and you won't have water in your oil any more. west