Hi Ian, how many pipes communicate with your tank?
I have some thoughts that really need a two way conversation to expand. If you send me a landline number to my e mail address I will go through it with you.
Regards Mel.

But there is no logical reason for it to boil over when parked downhill other than there being some sort of air block which when the angle of the engine changes then moves allowing water to touch very very hot surfaces then boiling.
Simpy parking on a slope want change anything.
So is it'boiling over' i.e actively boiling or is it just running out?

If it is activeley boing then I would suggest you need to make sure all air blocks are out. A lot of people with Cobra replicas have airblock problems.

I have definitely, as an ignorant newbie, had some air block problems, but I am more aware of them now. I am not entirely sure of the best way to get rid of air blocks though, other than applying water and waiting for the air to bubble through. Squeezing the pipe at the head of the rad seems to help, as does unbolting the expansion bottle and waving it around like some sort of a drip.

It does strike me that the radiator seems to be quite small for a big, 2ltr plus engine. How do V8 drivers cope? Does anyone fit an auxilary rad, or maybe an oil cooler?

When I had my Cobra, one of the tricks used was to jack the rear of the car up as high as possible allowing any bubbles to move (hopefully) up to the expansion tank. In my beast I had a Transit diesel Rad but you have to realise that, believe it or not the V8 doesnt get very hot.
In my Morgan replica I am building at the moment it has an RV8 in it and I have fitted and MGBV8 Rad in it

Hi Ian.

I just had a thought - I don't know if it's worth trying! A fairly recent development in the 'additive' market is radiator water 'wetting' agent such as Miller's Rad Hib Extra Cool stuff.

I understand it works by breaking the 'surface tension' of water (a bit like adding detergent to a pond and watching the 'Pond Skaters' sink...), which gives the water better contact with surfaces thereby aiding heat transfer. I'm actually thinking it might also in your case make any air bubbles less likely to 'stick together' forming air-locks, and more likely to 'creep' along the sides of the pipes and make their exit! With less surface tension, the air bubbles should break up into smaller ones, and could even be carried out by the water flow until they can exit the way they should!

(If you imagine a drop of water sitting on a water-resistant surface, it'll form a 'bubble' with only a small contact area underneath on the surface. Add detergent, and the water's surface tension is removed and the drop will spread out and flow out. It's been made 'wetter'!)

I've no idea if it would work this way, but it might!