Scooterotica

having problems sorting out the cooling on my dragster. I can fill the system up and bleed it ok and sort out any air bubbles as per the manual but once it warms up it blows the coolant out through the expansion bottle. any ideas what could be wrong?

Head gasket or blocked rad or blocked pipes

forgot to add all pipes are clear as they've been well flushed and the engine has been rebuilt with new gaskets etc. have read that the system should pressure up and maybe the seal on the cap is screwed

Seal on cap could be the problem as it is common ...but how much pressure are we talking in bottle as when they get too hot they push the water out the bottle ..that's why I said gaskets or rad or pipes ...as it could be overheating

Oh an did u bleed water system when thermostat was open ? While bleeding it

Had this on an old dragster of mine.........

Assuming that you have bled it properly, even when hot you should be able to run it with rad cap off.........should be fine.........any sign of too much pressure and blowing off caps, hoses (that's what it did with mine as they were external non kink ones) is a sign that all is not well head gasket end (as someone suggested).

Was it a new O Ring fitted? Mine was intact but just weak.........was putting pressure into the system.

New O Ring, no problems - ran like a dream after that

I had a similar problem on my sons dtr 125 yam it turned out to be the pattern gasket on the head got a genuine one from Yamaha and it was fine

I ripped my thermostat out as soon as i got my Dragster and have never bled the system yet and its been drained a few times ,As Carlos says Replace the o ring and a touch of silicon sealant ,Sorted