Oil is leaking from the bottom tie across hose on the radiator on my 2004 yamaha YZ 250F. Why?

SOURCE: yamaha yz 125 2001.water leak

Yes, the water seal is leaking. This is the indicator hole for the water and oil seal.
Enjoy the ride !

Jon

SOURCE: yamaha 2006 yz 250f gets over heated

Hello,

It is normal for the bike to overheat when idleing !

This bike needs air to pass through the radiator for cooling purposes. Air speed needs to exceed 40 kilometres per hour for effective cooling.

A good tip is to use only coolant in the radiator. Do not mix with water.

Cheers

Jon

SOURCE: how much oil for 2003 yz 250f fork seals

3 Pints is average but you can adjust it to your riding style and weight. Stock oil height is around 130mm from top but you could set it around the 110 to 100 range for increased bottoming if you do a lot of big jumps ect.. 5w oil is the usual weight but fork oil goes up to 20w.
-John

SOURCE: 2006 yamaha yz 250f starting problems

You may be having trouble with a sticking intake valve. Remove the valve cover and spray some WD-40 onto the valve and spring. Try to operate the valve with your fingers to work it loose. Once the engine starts running, it should improve. You may need to change the oil. Good luck.

SOURCE: 2005 Yamaha YZ 250f. suggestions on type of motor oil.

What did Yamaha tell you? I think 10 is too light. Call your Yamaha shop for the proper recommendation.