Extreme bubleing in expansion tank

A cooling system guru please enlight me: put new thermostat(genuine), filled the system by the book, insisted on releasing the air: attached a tube to the bleed hole and after i filled up the circuit with expansion tank raised as high as possible, put the tube into a can and with engine running untill coolant reached the max temperature passed through the system about 5 gallons of fluid by keeping topped up the expansion tank while the fluid flew into the can(i'll keep the extra for the next time ) on a second thought, after everything was ready i've realised that i could have inserted the pipe back into the expansion tank:doh: anyway, i'm sure no air remained there ... nevertheless after about 40km the gauge raised(not untill max. just to 2/3 cos i'm obsessed about it ) and when i checked i found the water like boiling in the tank and the bleed pipe which is coming back to the tank was pushed off by pressure. No oil in water, oil level OK.
... the only thing i must have done wrong is that i didnt wring the expansion tank's cap to maximum allowed ...could that be the reason or what

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if it is 300tdi check the valve to header tank is ok. If pipes are cold anywhere then you have airlock (release header cap and then loosen pipe clamp and pipe can then be pulled off slightly to allow any air lock to go)

Or you may have headgasket failure

Thanks for the reply m8 .... is what u say similar for Td5? ...i didnt mention it cos it's in my signature ... by the way if it's a head gasket failure shouldnt it be oil in water?

oil and water seem to rarely mix when an LR head gasket goes, the common failure links a cylinder to the water circulation, so bubbles and gurgle more often than gruel in the sump

but there are many other reasons to get bubbles in the coolant