Why does oil smoke come out of the oil cap??

[glennj3]

My MC 170 had a plug type oil cap, this 165 has a cap with fiber inside and small holes around the lower portion. When driving I see oil smoke coming out of the holes and the smoke oil builds up and runs down the valve cover.
Should I try and replace the cap with a sealed one or is this a breathing issue the engine needs?

 

[dan t.]

Re: Why does oil smoke come out of the oil cap??

Every engine needs to breath, if it didnt crank case pressure would build up and blow out the gaskets. You should have some kind of a tube running from the valve cover to the spark arrestor, if you do you dont need a vented cap. Personaly if it was mine I would put in a pcv system.

 

[stonyloam]

Re: Why does oil smoke come out of the oil cap??

Does it have the original valve cover, like your 170? It sounds like someone put an automotive valve cover on it. All (as near as I can tell) of the 470 valve cover should have a oil plug and a fitting for a vent tube that goes to the flame arrestor (like your 170).

 

[glennj3]

Re: Why does oil smoke come out of the oil cap??

It should be the originol, it has the #'s on it. It also has a tube going to the flame arrestor but right off hand not sure if the tube goes into the valve cover or not, will check. I have a used 470 in hand, that V cover does have a plug, it is not the same size as the 165.
My 175 had the plug also.