A few things that should be considered here.
First, yes, you can use your bulb type tester, with accuracy, and no problems.
Second, you will find that the ideal 50/50 mix, if changed, can at times, cause a temperature change, here is why.
As we all know, antifreeze is thicker than regular water, so it does not flow as easily as water. Therefore, convection of heat is not as efficient, so if you have a higher concentration of antifreeze, you may not cool as well.
Remember that 5050 is the best compromise between corrosion protection, and cooling of the engine.
Just a few thoughts, c4c5
c4c5 Chevrolet dealership mechanic, ASE Master Technician w/L1. COFFEE ADDICT. A persons judgement is only as good as the information they have, which should be FACT, not fiction.