I have been riding my 2006 Scorpa SY250r and getting some dribble out the overflow. I suspect it is either simple a bad radiator cap or head gasket leak. The fan is turning on, the fins are clean, and the coolant level is only just above the fins. Every ride it seems to let out maybe 15ml of fluid.

Before I start replacing parts any test for what could be wrong? I I tried something very simple where I filled the overflow tube with coolant and then squeezed a radiator hose and it did push some of the coolant out of the overflow (presumably air escaping the radiator) which would seem to indicate the cap is bad? Here is the video:

Is the cap specific to Scorpa SY250r or are the interchangeable over different makes of bike?

Edited June 15, 201412 yr by j__h

Every bike will dribble if you top it off. It`s been this way since they did away with the over flow bottles.

Every bike will dribble if you top it off. It`s been this way since they did away with the over flow bottles.

Yes I am aware of that, I have not been topping it off and I actually think I have put the coolant level below that which is called for in the manual (I have it just about at the fins which leaves a large area for air). I even took some coolant out with a syringe after a few rides to see if it would continue leaking, and it did on the next ride.

Edited June 15, 201412 yr by j__h

Hi jh. I watched your vid 3 times and cannot see whats going on. I was expecting to see fluid flow into the syringe but cant see it. Sure its there but I dont think the vid shows enough for us to go by. Might be a cap issue but sorry I cant offer any help otherwise.

Yeah it is just a little bit leaks when the line is first squeezed.

Here is another thing i tried. Blowing into cap when forming seal with my hands, the bubbles are coming out the overflow, there is no way i can produce 1 bar so i highly suspect cap is bad.

Rad cap test 2:

So now time to source a cap. I presume there is no interchangeability with other bikes?

I`ve seen more than a few things, but never a cap. It was around `95 and Gas Gas USA was talking about caps. A garden hose washer was the cure. It is worth a shot.

Almost sure it will be radiator cap, i replaced two (in 7 years) on mine.

May just be worth nipping the radiator cap tags just a little. This will tighten the cap on to the radiator a little more. If seats the cap better with a little more pressure. This once resolved a similar issue I had. Worth a try and costs nothing...

Loonal

The cap appears to provide its own surface for the pressure seal. Thus having it on tighter will do nothing if it is not leaking from around the cap itself (which it isn't). Thanks for the tip though, could help out on the other bikes.