Hi Pete, sorry, I've been away for work for the last fortnight.

Well I had it running for 20 minutes or so the morning before I left, but just idling in the garage while I mucked around with the timing. It spat out a little coolant but I know I filled the rad too full, so it would've just been that I'm thinking.

But looking at the two caps and the length of the neck, I can see that even without any pressure, the old cap would have been sitting above the hole for the overflow hose, so I'm pretty sure that will be it.

I can't test drive it just yet as I'm replacing the dizzy with one of ConvertibleMini's you-beaut' electronic units. I just got back today and have a couple of parts to change and timing to reset before I move it anywhere. I probably wont get around to it until later next week...

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'77 Leyland Mini Van

When you sort out your cooling problems you might want to do what I did with my clubbie and that is fit an expansion tank to your radiator overflow pipe.
As the coolant expands, it flows to the expansion tank and is stored there until the engine cools. Mine is off a moke and as long as you keep the overflow tank at least half full, the system works well. good luck.