Castrol coolant test strips - limitations?

If you're not sure about the state of the coolant, just change it?

Indeed. Seems pointless to piss around testing for the sake of a few quid's worth of coolant and an hour or so.

But I can't see the point in used oil analysis, for the sake of a change, either.

That seems to be a US thing. Even when they change it every 3000 miles. ;-)

But it's also the place that Toyota and others have had had massive sludge problems.

On a fleet of HGV it's worthwhile.

Clearly a sudden rise in metal content will tell you that a bearing is losing it.

Joking. You can't fill up with a few quids worth. That could get you a bottle of inorganic inhibitor concentrate, and you mix with rainwater. That would only be suitable for old cars in temperate climates.

But here is a scenario: a few years back, my sister's car blew a hose, she got it towed to nearby garage. They fixed hose and put new coolant in at a hefty price. It looked like red cordial to me. I borrowed a refractometer, and measured it to be only 5 to 10 % glycol, which is useless. So threatened them with complaints to consumer protection and got it changed.

The level of glycol cannot tell you how old the antifreeze/coolant is. Coolant should be changed on a timed basis as per makers service schedule.