Or you could just replace your coolant every two years with green Prestone and not worry about it. Thats what I do in all of my vehicles.
Two gallons of Prestone is cheaper than $30 for PH paper.
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Green Prestone is a high quality non silicate coolant, which is the correct coolant for our cars. I ran the OEM blue stuff in my car until 100k miles. I then flushed it and switched over to green Prestone. I then flushed and refilled with green Prestone at 200k miles. My car has something like 235k miles on it and is doing fine.
I'm assuming you're using this version of Prestone?
https://prestone.com/products?detail=AF6300
It states it's compatible with Mitsubishi but states it is a POAT type coolant but not HOAT type coolant that the manual lists as required.
Page 9-7 of the owner manual states: Use “Mitsubishi Motors Genuine Super Long Life Coolant Premium” or equivalent high quality ethylene glycol based non-silicate, non-amine, nonnitrate and non-borate coolant with long life hybrid organic acid technology.
I use this and mix it 50/50 with distilled water.
https://www.walmart.com/ip/Prestone-...allon/16879960
Non silicate coolant. Toyota say to use Toyota coolant in their cars or else. Honda says to use Honda coolant or else. Mitsubishi would be telling us to only use Mitsubishi branded gas if they sold the stuff.
My car has over 234k miles and is doing fine with non silicate Prestine thank you very much. Obviously I’m an idiot so just do the opposite of what I’m doing and your car will be fine.
I just think it's important that the advice we give is consistent with the manufacturers recommendation which brings me back to my original statement. Just because you can use a non certified coolant in your Mirage doesn't mean that you should. You have a lot of miles on yours and maybe it's not that critical of a issue in your situation. But I think it's important to qualify recommendations so people that are maybe not as mechanically inclined as you are to believe that coolant type is irrelevant.
Are you using Mitsubishi certified PH strips?