Help: Coolant leaking during Refill

I've got a 2000 426 and I need a bit of help. I just drained the coolant from the radiators using the drain hole, (bottom hole on the waterpump cover), flushed the system with tap water, put the bolt back in and torqued it.

Then I started to refill the system and it simply drains out about 5 seconds after I pour the coolant in!?!?! It is not leaking out of the drain hole, but rather from either 1) under the engine someplace, or 2) from the tube that comes out the top of the engine and ends at the front-left side of the engine. I'm not sure where exactly it is draining. Anyone experience this before or have any ideas? I'm hoping to ride tomorrow, but I might be out of luck.



I went out to add more and see if I can tell where the leak is, and it appears as though it is definitely from under the engine as it does not appear be be coming out of said tube.

I'm open to any suggestions.

This same thing just happend to my friend's '98 YZ400F last weekend.

You have a blown water pump seal. A new one wont cost much.

Thanks for your input, Doug. I'll have to investigate further. Any idea what can cause this? The only thing I've done is remove one bolt, drain, and replace bolt. It was holding fine one minute, then 5 minutes later it held absolutely no water. Leaks out as if there were no seals anywhere!!! I'm still mystified, so any further insight is still appreciated.


Yeah, that seems weird, but it does sound like your outer seal, so chalk the timing of its failure up to coincidence.

I've had one fail on my '00 just like that, I rode all day w/ no problems, rode it up the ramp into my pickup bed and it puked everything out on my boot just as I killed the motor.

When you replace the seal inspect the shaft for a smooth finish, if it is badly grooved replace it. And pay attention to how the old seal is oriented when you remove it so you don't put the new one in backwards (not an altogether uncommon mistake).

Hope this helps.

How much is draining out?

How much is draining out?

All of it.

Well, thanks gentlemen. I'll pull it apart tomorrow.

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