Coolant...

[oj88]

I don't think you need to use coolant for top-ups. Distilled water is better.

Normally the cooling system is sealed and it will only lose coolant through the overflow tank. But when going into the overflow it's only water that gets turned into steam and ends up there, the ethylene glycol (boiling point 197C) and other additives in the coolant remain in the radiator loop. Thus topping up with coolant slowly increases the coolant concentration in the engine with each top-up. Topping up with distilled water replaces only the water that was displaced and keeps the coolant concentration the same.

So what's wrong with increased coolant concentration? The cooling capacity mostly comes from water, not coolant.

Water has a specific heat of about 4.19J/g-C. Ethylene glycol is only a bit more than half that at 2.36J/g-C. The commonly used 50-50 mix is 3.56J/g-C, but you can see that most of the cooling will be coming from the 50% water mix. As the amount of water in the coolant is reduced, the cooling capacity reduces sharply until you end up closer to the 2.36J/g-C of ethylene glycol.

OTOH a 75% water / 25% ethylene glycol mix will have a specific heat of 3.93J/g-C, which is a lot closer to pure water. We don't really have winter so the anti-freeze properties aren't as needed. We just need the additives in the coolant that prevent galvanic corrosion, and this can be done with as little as 15% anti-freeze.

I disagree and wouldn't advise that.

Additives get used up too, so topping up with the proper coolant in the correct concentration is the only way about it. I use the Toyota SLLC pre-mix to remove all the guesswork.

The Toyota SLLC has EG, DEG, additives, and deionized water... which is NOT distilled water.

Several warnings in the manual:




But to your point, having water in the system is better than having no coolant, so it can be used in an emergency. But it must be flushed out as soon as possible or corrosion and other nasty things can happen.