I have a basic question related to testing my coolant.

My understanding is that coolant needs to do four things: transfer heat, prevent corrosion, not boil, and not freeze.

I have a basic hydrometer that tests only the freeze point. My question is: can I assume the the properties of a coolant, its abilities to do what it's supposed to do, deteriorate at approximately the same rate? So that, if the freeze point is still very low, I can assume that the boil point is still high and the corrosion prevention still intact.

Or conversely, is it possible that the deterioration of the properties will occur at significantly different rates?

Thanks.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 178k mi, Stage 1 tune, tuned TCU
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