Suspect Coolant System Issueai

I'm new to the forum and am seeking any advice. I'll try to keep it brief.


Bought a 2005 yamaha wr450f recently. I'm not a mechanic, but have rebuilt a couple of carbs and rebuilt this one knowing that the bike sat for awhile. Bike runs good. I've ridden it twice around the neighborhood for about 10 minutes at a time. Live in South Florida.


Did an oil and filter change and was surprised to see that the old oil looked watery, not thick like oil usually looks during an oil change. I don't know if the liquid coolant system is working and don't know how to check it. I read in another thread that if the oil looked milky, it's possible that the head gasket needs to be replaced.


I plan on running the bike around the neighborhood a few times and then change the oil and filter again to see if water is getting into the oil.


Any tips on how I can verify if the coolant system is working? If I find that the oil is watery again, what are possible problems? How hard is it to take apart a 4 stroke engine and replace the head gasket or whatever it is you think I'll need to do?


Thanks in advance for your comments and advice. Love the forum and love working on dirt bikes. I also own a 2006 Yamaha TTR 230.



Watery as in thin?

This is normal.

When oil breaks down it becomes as thin as water.

The PO just didn't change it often enough.


If there were water in the oil, it would be white and milky.


You cannot judge an oils quality by it's 'thin-ness'. 


You test the cooling system by opening the radiator cap before your start the bike and watch to see the water churn.

Put the cap back on, and let it warm up. 

There should be no leaks anywhere, and the cap should be under pressure (careful, the water will burn you)

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