Engine Coolant Testing

I picked up an engine coolant tester, my coolant is testing at -17 Celsius, but should be -37 Celsius with 50/50 mix.
Question: Do I add green coolant to get to -37 Celsius or do I add
water to the resevior?
My bad: I flushed out the engine a year ago when I changed the thermostat but was in a hurry and didn't mix correctly. Haven't had any problems to speak of.
Thanks, Matt
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opined in

I'd drain the overflow, then about a quart to 1/2 qallon from the radiator and refill both with the concentrated green stuff .. you certainly wouldnt add any water. -37 isnt a magic number.. just keep an eye on it and any time you add, make it concentrate until it gets there.
That's why you should premix before you replace. MAKE SURE what you are using is concentrate. A LOT of places are selling pre-mix.
--
- Yes, I'm a crusty old geezer curmudgeon.. deal with it! -

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I'm certainly not that precise! The guage just indicated that -37 C was about a 50/50 mix. Thinking back now I realize when I flushed the block there was a lot of water left in their below the radiator return line. That 'splains it.
Thanks! Matt
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