Very unlikely your car will have a drain tap on the bottom of the radiator. These generally disappeared years ago.

Today you usually just pull the bottom hose off.

Think the factory fit Ford coolant is 10 years between drains. Our dealer always used to check the properties at a service, at 6 years it was still well up to the job.

But remember its not just the antifreeze properies. It also lubricates the water pump, acts as a summer coolant and prevents corrosion in the engine.

Its ability to do all these gets less with age and I am pretty sure the tests only check the freeze point.

Changing it only costs a few pounds, indeed when the cam belt/waterpump are changed (on a 2 litre petrol) after 100,000 miles 10 years as per Fords schedule it gets changed anyway.

I used to syphon some out every year (into a yoghurt pot) and pop it in the freezer (-20c). If that came out liquid after an overnight stay, I assumed it would handle anything our climate could throw at it.

They only drawback to that is it doesn't check the corrosion inhibitor aspect of the stuff. I've learned lately (and experienced) that the corrosion inhibitors can 'settle out', particularly in thermo-syphon systems, leaving a sludge that can block the cooling system. As most cars have had water pumps in the last hundred years, this aspect isn't likely to bother many.