BMW coolant freeze point question
I have some OE BMW coolant around and it says on the bottle that a 50:50 mixture will give you a -40*C freeze point, so i decided to test it out.
I poured in a small recipient equal amounts of antifreeze and water and then tested the mixture. It said -18*C!
I repeated the process, put same amount of antifreeze, but half the amount of water - and it reads -25*C!
I don't understand, what's wrong?! How do i get it to read below -30*C?
I used the same tester to test a fresh mixture of antifreeze on another car (Peugeot 207) and it reads precisely -37*C, as it should.
I tested the bmw antifreeze alone and the tester goes off the scale, so it's concentrated, not pre-diluted.
BMW 320 dA LCI, BMW PPK - 197HP, 2010, sapphire black, steptronic