- Remove the radiator cap
- Top up the radiator
- Leave the cap off (counter intuitive, I know.)
- Lean the bike as far as you can to the left (just before the fairing touches the ground)
- Stand it up
- Top up the radiator
- Lean the bike as far as you can to the right - Stand it up
- Top it up again
- Replace the radiator cap
NB: As you lean the bike over, you will hear the trapped air rising to the top.
Follow this link to YouTube for a better method, using vacuum, which can be done without help You'll need a vacuum pump (like you would use to bleed brake lines), a modified radiator cap, some hoses and catch tank.
Follow this link to YouTube for an even better method, using a bleed hose For this to work, you must removed the degas hose from the thermostat housing to the radiator cap, and seal off that nipple using a short piece of hose with a stopper in it. A new hose is added at the thermostat housing which leads to the right side of the frame just above the engine, but inside the fairing. That hose has a brass stopper in it, with a nylon washer & M3 screw to seal it off. It becomes the bleeder. Attach a clear hose to the end of the bleeder (with the screw removed) and take it higher than the radiator cap, then down to a catch bottle. As you fill the system from the cap, the coolant will rise until it appears in the clear bleed hose. As air escapes, it bubbles up through that hose. Squeezing the radiator outlet hose will eject air from that airlock to the radiator. When no more bubbles show up, the system is airlock free and the bleed hose can be resealed./p>
The radiator cap pressure is 1.4 (units?), and the seal is 25mm (not the original 22mm, which leaked)
While we're on the subject - Topping Up
The manual will tell you to keep the overflow reservoir between the min. & max. marks - don't bother. It'll only be there when it's hot - if it feels like it. If you are just under max when cold, when the engine warms up, the Tre will dump it on the ground, or more correctly, over the engine - see below - unless you add some hose to it to let it discharge through the side aperture of the bottom fairing.
Check the fluid level the easy way - only when cold, and then by removing the radiator cap. You may see the fluid just below the cap seal. If not, add a little. It's probably lurking in the transfer tube, and will only take a thimble full.