Hi I have tried to search for this but can't find an answer so have ended up posting this. I have a 2 litre pinto which has the old radiator with a push pressure cap. Because it is sitting under the nose cone it makes it difficult to check the level, therefore I wanted to plumb in a header tank so I can check the level from the bottle rather than take the nose off to check the level. The header tank I have got has an outlet at the bottom with an overflow by the cap. I think the bottom should fit into the bottom hose that goes to the bottom of the radiator with the overflow connected to the overflow of the radiator. I did connect into the pipe from water pump to inlet manifold but the bottle filled and overflowed as it heated up. If it does go on the bottom hose any ideas as to who will do a joiner to go from large bottom hose to small header tank size hose.

Having two pressure caps on a system is asking for problems with airlocks some builders have got away with it but they have been lucky.

If your existing Ford rad is in good shape you could get the rad cap fitting removed and blanked off -- not a major job.

Alternatively fit a Polo rad not that expensive.

If you want to use your existing tank connect it to the top of the cooling system, however I would suggest a Rover 200/25 expansion tank which has two connections one of which goes to the upper part of the cooling system and the other to the bottom hose.

Cheers might look into that, any ideas on who or where would blank off the rad and any idea of cost

Car Builder solutions do a takeoff that fits in the bottom hose
You can fit a higher pressure cap to the radiator than the header then the header will open befor the radiator
T piece off the small (16mm) manifold hose to top off header tank

It is not that simple

The problem is the radiator cap actually contains two valves, the second valve is a vacuum relief valve to draw air into the system to prevent the radiator crushing under atmospheric pressure.

The reason why two radiator caps is a bad idea is that air will be drawn back in by both routes, in normal operation this air is expelled as the coolant warms up.
If one pressure cap blows off at higher pressure than the other air will only get expelled via the lower pressure cap. After a few warm-up cool down cycle this can cause an air lock and coolant level in the radiator to drop even if the header tank level is normal.