Hello, I'm wondering which coolant type is the best in our time? Specially for old cars, I drive a 2002 Ford Explorer Sport Trac with 4.0 V6. I'm using valvoline zerex g-05 and used the pre-mix first then switched for fully concentrated one since I've seen videos recommending it over the pre-mixed with water. What you do guys think about this?
the pre-mix is best cuz you're always supposed to have 50/50 water coolant plus if you use tap water can have many minerals that can end up destroying an engine where the mix has purified water already in it
Thank you Mr.Kilmer ! I also have another question I posted long time ago. Can you please check it out? Here's the link: https://carkiller.com/scottykilmer/qa/ford-explorer-sport-trac/
I'm even cheaper than Scotty - I make my own pre-mix. I buy the "concentrated" stuff, pour half into an empty antifreeze bottle, and mix in distilled water in each bottle which is generally available for under $1/gallon. (Paid 80 cents/gallon just yesterday.)
I've been doing this since before the 50/50 mixes were popular over the counter. Much cheaper than buying the premade mix and it's just a few minutes work.
I'm even cheaper than you. I do that but with tap water 
You can't go wrong either way but I buy the premixed because it ensures that I don't accidentally get the mixture wrong.
For ease and peace of mind, I’d just stick with pre-mix.
Never use concentrated antifreeze. You will overheat the engine. It must be mixed with water.
Either coolant is fine, … problem is with mixing it with water.
Premix is a problem when you flush the system with clean distilled water, presumably drain it, … and than fill it up with a 50/50 premix. Well, … you never drain that flushing water completely, and so you in fact will end up with something like, … say, 65 water and 35 glycol mix, as a result. Trust me, … Is that good enough for you? Probably not.
Full strength is of a lesser problem. You find out what is a total cooling system volume for your car, … and than divide that by 2. Next, you flush your system with clean distilled water, drain it, and than pour 1/2 of total cooling system volume with concentrate liquid. Once that is done, … top it up with clean distilled water. That way, you will end up pretty close to 50/50 mix.
It works every time, … and total cost for distilled water and a concentrate will be less than the premix tab.
… and just to be absolutely sure, get yourself a cheap hydrometer and check density. You most likely be pretty close on the 50/50 mark with concentrate and not so with premix.
F.S.
