Hitchcocks Forum

What comes out of my crankcase breather looks like mayonaise. Do I need to worry about that ? I checked the oil tank, and the oil looks normal.

Yes and No. What model bike and year? It is usually a sign that there is a kink or other obstruction in the breather pipes...


Yes in that the elephant snot can 'pack-off' the breather lines and end up filling the air box (or elsewhere) with the glop AND oil. (You can end up with a very low oil level)


No, in that if the bike is used mainly for long trips it usually dissipates prior to accumulating.


If the Bike is used mainly for short trips, consider changing the oil more frequently and using a lighter W oil..?


Otherwise the long term solution lies in refitting the pipes to eliminate any 'rise and falls' which allows the 'snot' to drain to - build up in.

It is a Jan 1999 500 cc Bullet. I do mostly long trips, i.e. minimum 50km and mostly more than 100 km. I never do short trips with it. I change the oil every 3000 km. Use 10W50 oil.

Does your bike still have the small rectangular breather box under the battery? And if so, does the breather hose of the motor curl UP or DOWN to bypass then points cover?


Up is preferred, Down allows condensate to accumulate.


Do you still have the short section of "Duck Bill' inside the 'catch-can?, it is important.


Or, if you simply have the older pattern Duck-Bill hose that is venting over the gear box sprocket, you may want to consider a lighter oil; 10/40.


DONT shorten the flap on the Duck bill hose!

Wasps nest... stick... poke.


I have a 2003 Bullet 500. The tube coming from the breather has always hung down under the timing. The catch can under the battery gets regularly drained. Thick black oil comes from it. Not much, but I check it regularly.

As far as I know, the mayo is a mixture of water vapour and oil mist formed in the engine. Quite where, I'm not sure. Most likely, the crank case. I'm just glad that it leaves the engine.

The oil has emulsified with water. These engines run cool, as mentioned on other posts here, the temperature in the oil reservoir seldom reaches more than 55/60c which is not hot enough to vaporize the water. Water will displace the oil in bearing surfaces causing rapid wear and pitting to bearings. Drain it and replace with fresh oil as necessary.

The rubber tube goes down under the points cover. Yes, I still have the old catch can under the battery cover. The catch can does not accumulate much oil. I regularly drain it, and what comes out isn't much.

Thanks to everyone for the replies.
I don't worry anymore. I just remembered that mayonaise-looking oil in a car generally points to a blown cylinder head gasket. Apparently, not in the case of the crankcase breather.

As you say, mayonnaise in a car engine is a sign of a blown head gasket. Another sign in a bad case, is water will cause the oil to rise above the normal level, which should be looked for when buying a second-hand car if that particular model has a reputation for having head gasket or cracked head problems, which is the case with some model Ford Falcons in Australia.