Oil in the Breather Hose


I just put the clutch kit in and then changed the oil. Now oil keeps getting in the air box.

I can add oil to the recommended safe point, then drive it and the oil runs out till it gets to the lower line on the dipstick then it will stop putting it in the air box. I have checked filter is in right and is in the right one. I need some advice bad its very frustrating. {Philip, MS, USA ~ 2006 Honda Rancher TRX350 with HMF pipe, KN filter, snorkel, jet kit, clutch kit}


It sounds like you have really take care of your quad. Wasting oil for no apparent reason would frustrate anyone. I just want to say that as long as the oil level is somewhere in the acceptable range on the dipstick, you are not in danger of damaging your engine. You do not have to keep adding oil to maintain the maximum amount of oil that the engine will hold. That is why there is a top and bottom line.

If you are putting around the yard towing a garden cart, never going more than seven or eight miles an hour the engine will hold more oil and not throw it into the air box. If you are racing the quad, the constant throttle and rapid acceleration and deceleration will send oil to the airbox due to the increased oil pressure.

Drag racers and new riders can have this problem also. They typically hold the throttle open to accelerate and then just let go of it to slow down. That said, all signs point to the breather hose from the engine to the air box.

The first thing that I notice is you say you have a new or aftermarket snorkel on your Rancher.

When this snorkel was installed did you move the breather hose? If it was removed to enable you to access and replace the snorkel, it may have been reinstalled incorrectly. If it is too low it could cause excess oil to reach the air box during acceleration.

Check to make sure it is properly routed and is not bent or crimped. If there is a tight bend in it, the engine will be able to force oil into it when you accelerate but the oil will not be able to drain back into the engine when you decelerate.

If you have a lot of miles on the ATV or hours of hard riding, you could be in need of new piston rings. During acceleration the compression of the engine will push oil past the rings, into the crankcase. Then it will migrate through the breather hose on the air box. Once there, the only way it can get out is through the drain tube on the bottom.

This is what is supposed to happen with motor oil.

It is why you have the breather hose to the airbox and the drain tube in the first place. It keeps the oil pressure in the engine from reaching critical levels & blowing out a gasket.

I assume that the machine is running well, with no loss of power or compression in conjunction with the oil problem, or you would have mentioned it. When the rings are worn, the engine will loss compression and you may see a bit of grey smoke in the exhaust as some oil, that is slipping past the rings, gets burned during fuel combustion.

So if your compression is really high and you are not ready to replace your rings you can try replacing the breather hose.

Replace your current hose with one that is a few inches longer. Route it in such a way as to make it go up higher before in comes back down to the air box. Just take care not to kink it. This will enable the oil to drain back into the engine after an aggressive acceleration or rapid deceleration.

Drag bike owners usually take it a step further. They purchase flexible copper tubing and bend it into a vertical cork screw or pig tail shape before using it to replace the OEM breather hose. This ensures that the oil has a much greater distance to travel before reaching the airbox. Oil goes into the tubing and works its way round and round the cork screw, but never gets to the airbox, it just drains back into the engine at the end of a run.

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