Why Is There Oil in My Honda Motorcycle's Airbox?

What does it mean if you find oil in the airbox of your Honda motorcycle without having overfilled the engine after a fresh oil change? You might have to do a leakdown test to find out.

Partzilla’s Honda motorcycle expert John Talley livestreams Q&A sessions on our YouTube channel every Friday at 3pm Eastern. In this session, John was asked what could be done about engine oil in the airbox of a Honda Africa Twin motorcycle.

Motorcycle leak down test oil in airbox

Honda Africa Twin Oil in Airbox Q&A

I keep having oil getting into my Honda Africa Twin’s airbox. Every time I park, oil drips out the drain hose on the ground. Not overfilled, fresh oil change. How do I stop this from happening?

John Talley: Well, that’s a little bit disconcerting because really the only way oil is going to get in your box is through the breather hose that’s coming off the side of the engine. Because the crankcase has to breathe. And that’s telling me it’s getting a little bit too much pressure in there if it’s pushing oil out of the crankcase up into the airbox. So I would be a little concerned if you’re getting too much blow-by on your piston rings. It may be time to do a leak down test, which is different of course than a compression test. Because it’s going to be held at — well you’ll do one cylinder at a time — each one at top dead center. You’ll pump air into it, and then you’ll listen to see if it’s having an unacceptable loss. And in your case, you want to see if it’s losing more than I’d say 5%, and it’s heading down past those rings into the crankcase itself. Not overfilled, fresh oil change? It shouldn’t be happening as long as you’re not overfilling it.