Odd one this..

The old V8 has a coolant leak, it is dripping off of the bottom of the bellhousing i've removed the bell housing inspection plate and had a root around and oddly the inside of the bellhousing looks dry even the bottom feels dry if i root around with my finger, it just seems to leak coolant down the joint between the engine and the bellhousing.

The odd thing is she builds pressure in the system just fine, however if I remove the expansion tank cap and relieve all the pressure the leak stops immediately..

refit the cap and let it pressurise again and the leak returns.

My head is saying its got a headgasket leak from the coolant gallery and its weeping out when she's building pressure??

Another issue "or is it" is the coolant has a fair few big bubbles in it when shes running with the cap off, could be paranoia or is that indicative of a headgasket?

Any advice appreciated.

I think your head might be right. I had a similar leak a few years ago. It was leaking from the back of the left head to intake manifold joint, and dribbling down the back of the engine, dripping off the bell housing.

I had a similar leak that came from the top hose. The clamp wasn't sealing perfectly so when pressurised it would drip down onto the valley gasket and flow back and leak down between the block and bell housing. I initially thought it had to be the head gaskets as I couldn't see how water would get so far back.

Rear welsh plug.

What about the valley gasket?

When I stripped mine down for the first time, the valley gasket was in a right state. Oil and coolant all over and around it and a really poor fit. Depends if you can see if the coolant is coming from that high up I suppose.

Or as you say, maybe the head gaskets... I guess the gasket could have failed at the very back, as the coolant channels are on the end of the block. Mine failed between the cylinder and coolant channel, so I could test with a dye kit for exhaust gases in the coolant tank.