Originally Posted By: boom10ful
I agree that these testers aren't very accurate, but from the factory it should be 50/50 no? Its an ethylene glycol tester; the ones that have a big needle inside. I've tested it on a premixed 50/50 and its right at the 50% mark. I've also tested it on pure coolant and the needle floats right up.
I don't know what the factory puts in for concentration, on my Toyota vehicles they recommend a 60% mixture and allow up to 70%. It's not a matter of accuracy (the tester should be fairly accurate) it is a matter of the upper range.
You could try mixing water with some of the coolant and see what that does to the measured concentration.