99 YZ400F Loosing Coolant

My YZ400F seems it is loosing coolant. It doesn't seem to be over heating on the trail and loosing coolant, yet weekend before a ride I check the coolant level and it is WAY low. Is there some sort of seal that could have gone out?

My YZ400F seems it is loosing coolant. It doesn't seem to be over heating on the trail and loosing coolant, yet weekend before a ride I check the coolant level and it is WAY low. Is there some sort of seal that could have gone out?

Brock,

I assume it's loosing more than it was before under the same conditions?

I'm thinking that tight trail riding could cause the radiator to boil some water out thru the overflow, which would cause the drop in level. That's happened to me under slow running conditions where it would naturally get hotter.

I have a 98 YZF400 and it looses coolant as well.

Its a motox bike so it hates to sit still when its running.

It was designed to constantly be on the move.

Mine shoots out of the overflow tube when I sit at an idle.

I havent found anything to prevent it from happening.

Just stay on the throttle.

Have you checked your engine oil? Is it milky?

My '00 426 loses coolant as well. I've done 2 scrambles races now and both times I have to add coolant. No evidence of anything in the oil so I'm assuming it's just boiling away from running so slow in the tight woods.

Check the condition of your radiator cap....if it prematurely spews coolant, then you are more likely to "boil off" more than you should. Honestly, I've trail ridden my '98's and now my '05 YZs with never losing an ounce of coolant. Whether it be in the heat of the summer in Florida or south Texas. I guess I've just been lucky, but I don't let it idle at a standstill, either. One thing you can do if the coolant loss persists is to raise the pressure of the cap. Instead of using a 1.1, use a 1.6 (from a KX500, worked on my WR).

And no, I didn't have any problems with hoses or seals after I increased the pressure.....

'99 YZ 400F, I do lots of woods riding with it, '02 YZ426F track bike, neither uses or loses antifreeze. Check out Royal Purple's "purple ice" product literature. It explains heat transfer pretty well and gives test data. Run more water for better cooling... Most guys seem to use 60/40 (60% ANTIFREEZE) thinking that boil over will be at a higher temp (it is), but what happens is that the fluid gets hotter 'cause it can't x-fer to the radiators as efficiently. You'd be better with 30/70 and your engine would run cooler.

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