Why Is There Water in My Yamaha ATV’s Oil?

You’ve changed the water pump seals and the head gasket, but you’re still finding water intrusion in the engine oil of your Yamaha ATV. Now what? We may have some very bad news for you.

Partzilla’s Yamaha ATV expert John Talley hosts live Q&A sessions on our YouTube channel every Friday at 3pm Eastern. In this session, John was asked what else could be the problem when a Yamaha YFZ450 has water in the oil even after a head gasket and water pump seal change.

Yamaha YFZ450 engine oil

Yamaha ATV Has Water in the Oil Q&A

I have a Yamaha YFZ450 that had water in the oil. I replaced the water pump seals and shaft and I still had water, so I replaced the head gasket and the oil is still a light grayish color. Any ideas?

John Talley: Well, you’ve hit the two main areas where it usually comes in. I hate to be the bearer of bad news but if it’s not just leftover water in there from not flushing it, chances are you may have a cracked head. I mean, you’ve done what you’re supposed to do. You went ahead and did the main seal for the water pump and then the head gasket, so that tells me it’s probably working its way into the head itself, because the head’s cracked. That would be my guess at this point. 

Buy Yamaha 10W-50 ATV oil

Buy Yamaha ATV oil filter

Watch the video below to see how to change the oil and filter in a Yamaha YFZ450 ATV.

Watch the video below to see how to do a top end rebuild on a Yamaha YFZ450 ATV engine.

Watch the video below to learn about common causes of engine failure and why they blow up.

Want to see more live repair questions answered? See more motorcycle and ATV repair questions answered here.