middle header tank between the V
 

got a problem with my 1999 748 bp and the middle tank between the cylinders can someone explain to me the purpose of this tank is it to catch excess water or to hold water when the sytem gets pressured mine keeps filling up but the bike is not over heating never go's past 180 f ??

will the water inside the 2nd tank return to the main header tank or will it just sit in there ??? i rode it up to manchester 170 miles and it was fine but on the way back i went a little faster due to it being dry roads and the water was all collected in the 2 nd tank whats going on i have blead the system and there is no block or air locks and both cylinder heads are fine ???????? is this just something the bikes do i cant see any water in the main header tank is there always ment to be water in there or will it siit in the middle tank then return to the main ?????? help !!!1

Maybe the cap on the Header tank just below the ignition has gone faulty and is bypassing water at to low a pressure, if it isn't faulty then for some reason you are pressurising your cooling system to much.
I'm fairly certain that once in the lower tank the water can not return to the main system

there are two lines into the header tank from the 2nd tank one is below the cap and one is about the diaphram on the cap the place that looked at it before said it was a faulty cap bmf this weekend ill try picking one up there hopefully

explaination of cooling system
 

The cooling system is partially pressurised (so boiling point is higher), and is controlled by the expansion tank pressure cap.
The tank between the cylinders is a "catch tank" for any coolant expelled as the system heats up and expands. Any fluid that is expelled will be "sucked" back into the main cooling circuit as the engine cools.
Most bikes that come into the workshop have a bit of coolant in the middle tank.......
A new cap for the front expansion tank is £8.16, and they can cause cooling problems.
Good luck at the BMF, make sure you remember where you park the bike:lol:

[Edited on 17-5-2006 by mitchc]

anyone going to the bmf and can bring me one (header tank cap) i can meet up at the DSC tent if its there this year my local dealer cant get one till middle next week