Another ER5 coolant leak - and some general questions

[drmick]

Hi.

I've read a bunch of threads about ER5 coolant leaks, but they don't quite match what I'm seeing with my ER5.

* When the engine is cold, I see no leak.
* After riding for about 1 or 2 miles, coolant is *pouring* out of the drain hole on the right-hand side of the engine casing, giving me a very wet right leg.
* By the time I get home, there's no sign of a leak (and there's still coolant left in the system - I've checked, and I think it's losing about 200ml to 300ml each time it leaks like this).

When it's leaking, I see no wetness around the filler cap, thermostat or top end of the water pipes - it all seems to be coming from way down the bottom end of the pipes, only on the right-hand side of the engine.

I *think* the leak is happening when the engine is warm, but before the thermostat opens: there's enough pressure to push coolant out somewhere, but the pressure drops once the t-stat opens. Does this sound likely?

Now, am I right in thinking that the only pressure relief is through the filler cap and header tank, or is there some other mechanism I don't know about?

If there's no other mechanism, then what's the fix? Is it just those damned O-rings at the bottom of the water pipes, or does it sound like I have a fault on the thermostat, making it open too late?

Cheers,

-Mick.