Posting this on behalf of my technologically-challenged neighbour:

It's a 2002 250 Pro. While draining the crankcase after a very wet day's riding, a not insignificant amount of coolant was noticed in there. Obviously not good. Any idea what could be the cause? Is there a seal behind the impellor somewhere that might have failed?

Many thanks for any and all suggestions!

I had a couple of water pumps disintegrate on me. Would be worth whipping the clutch casing off I think.

Just on the off chance - it turned out that all of my problems were down to the fan spinning at half speed allowing the bike to overheat and it seemed that the water pump was the weakest link. You can buy a kit to rebuild the water pump or get a new pump. Difference in price is not great enough to go for the kit if I remember correctly.

The fan gradually got worse until I noticed it. If it ever comes to replacing the fan don't buy a 2002 one. The 2003 fit perfectly and are a more sealed unit. Not sure about the 2004 but the 2003 was fine anyway.

Could be any number of other things probably, but worth a look.

I'm assuming your referring to the transmission, not the crankcase? If it is truely in the crankcase, then it's likely a bad head gasket..or oring in this case.

If indeed it is the transmission, then it's likely as BS said, a water pump issue.

My mistake: The coolant was in the transmission, not the crankcase and a water pump rebuild seems to have sorted it. I guess we'll find out for certain this weekend, eh Steve?

Make sure the fan's cutting in and you get a real good draught from it, otherwise you'll be rebuilding it again soon.

Mine turned in to a steam bike twice, heats up and destrpoys the pump, coolant in the oil, heats up expands and pops the oil level eye out the clutch casing - very dramatic.

if the oils gone white, then you will have to replace the water pump seal, happenend to my bike last year.

if the oils gone white, then you will have to replace the water pump seal, happenend to my bike last year.

Damm Gas Gas again eh gasserboy

Yeah last year

when you going to bring that scorpa out and put a nice few scratches on it??

Next trial for me is 8th May (Llangollen I think) can't wait