After some years of trying to figure out a few issues my 907 is back finally for some great riding. I have noticed though, a drop in coolant level after riding. Perhaps going through roughly 8 ounces per 200 miles. Although according to the temp gauge, the bike rarely reaches the halfway mark and this time of year, the fan only ever comes on when stuck in stop and go traffic. Of course coolant loss and overheating may only be related once coolant level drops too low to adequately cool the engine. I see no coolant leaks anywhere on the bike and no puddles of coolant under the bike. The oil level as seen in the sight window does not increase indicating the coolant is not disappearing into the case. Is it reasonable the coolant could be burned up by leaking into the cylinder? Like a bad head gasket in a car? The engine runs wonderfully without miss or hesitation. Also, there is no steam like exhaust coming out of one of the pipes. It's been a bit since I have done a compression/leakdown test but the last one I did a couple thousand miles ago was fine. Is it possible I have a leak but only at higher coolant pressure as during a ride? Although no signs of coolant inside the bodywork.
Any ideas?


Thank for any ideas someone may have.

These engines don't have a head gasket as such . The head to cylinder joint is metal to metal ( can be lapped if needed ) and the oil and water passages are sealed with a few O rings....... so if twer leaking from the "head gasket" you would see evidence of it on the outside of the cylinder. There is a small hole adjacent to the water pump on the front face of the LH engine cover and coolant can leak from there if the pump seal is shot ( actually if it is this its worth persevering as the seal is a carbon face seal and they can pack a shitty if ignored but can come right ). Other thing to consider is that the leak being small may be drying as fast as its leaking............8 ounces in 200miles is a good effort.... I have to make one last a fortnight

Hey thanks McTool for your ideas. So I will check it out. One thought is to ride it, get it up to temp and then park it in the driveway and check more intently. Probably remove the bodywork. Is there any way coolant could be leaking into the stator side without raising the oil level? It sounds as if the drain hole near the water pump would show any associated leaks there. With the promise of better weather here in Seattle soon, I'm likely going to have some time this weekend to do more investigating.

Cheers my Kiwi friend

If water was getting into the oil ( and I cant think where it would ) the oil would be a bit milky

Hi had a similar problem in that after a long ride I would check the fluid level and find that I had lost some coolant... but no obvious signs of anything. Eventually i went through all the drain bolts and hose clamps with a spanner and found the drain bolt behind the radiator was "loose". not enough for anything to leak when the motor was off but the combination of when the motor was running and up to temperature it was enough to let it leak... a little clean and nip up and no more leak.

It did encourage me to go off and get new silicone hoses and clamps though... mine were starting to look pretty sad.

P-)

I'll look into that some this weekend Bluey.
Thanks

I spent a couple of hours on the 907 today as it was yet again not riding weather with the rain and cold temps. Seattle is not riding heaven! I removed all the bodywork, started the ol' girl up and let it idle for about half and hour. In that length of time, the thermostat opened and the fan kicked on several times. The reservoir was topped off to the line before start up. With my flashlight, I checked all the coolant hose connections, the radiator, the coolant tank, the water pump side case, everything I could think of where a leak might be present. Nothing. No steam like a leak on a hot engine part would produce. no coolant on the lift anywhere. Nothing coming out of the side of the heads. No real signs on or near any of the hoses. There was a very small amount (two drops) of coolant at the hose to sending unit/switch tube on the right side. But that would not indicate anything like the level dropping as I have experienced. So in bewilderment, I tightened up all the hose clamps. I did not find any of them loose but a few were looser than they probably should have been.

The mystery continues.