[General] How to make a simple coolant filler adaptor

[Nut Kracker]

What you'll need
Drill.
Old radiator cap.
38mm or 1 1/2 inch hole saw.
Or one that suits the size of the bottle you're using.
I find the 38mm hole saw best.

1) Cut out the guts of the cap.
2) Remove and keep the rubber seal.
3) Centre the hole saw on the cap and cut the hole.
4) Using a blade, cut out the centre of the cap's rubber seal, slightly smaller than the neck of the bottle.
(I used a 2 litre golden circle juice bottle, as it has a flange at the base of the thread and fits nicely into the neck of the radiator).
5) Put the cap on the bottle and push the rubber seal over the thread.
You may have to bend out the locking tabs on the cap, so as it locks on to the radiator properly.
It may feel loose at this stage, but it will tighten to a water tight seal when you put it on the radiator.
If the bottle breaks or splits, it can easily be changed, by removing the seal and fitting with another bottle with a similar size neck.
Simples...