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.

[Dr.Kamiya]

I disagree and wouldn't advise that.

I think we can agree to disagree on this.

deionized water... which is NOT distilled water.

But I'm going to nitpick the point about deionized water. Distilled water also lacks ions, and is purer with less contaminants than deionized water.

[oj88]

I think we can agree to disagree on this.

But I'm going to nitpick the point about deionized water. Distilled water also lacks ions, and is purer with less contaminants than deionized water.

I want to be clear that I'm mainly against just putting in water (deionized, distilled, or tap - whatever the case may be) during top-up. Many owner's manuals details using 50/50 premix when topping up, so just adding water does imply that it will mess up the ratio and that's not a good thing.

I also read that distilled water's purity, and the lack of certain minerals, makes it unstable/unbalanced and can actually attack the cooling system (causing corrosion, scaling, etc.) The coolant solution still inside will no doubt take up most of the slack. But the irony there is, the supposedly "pure" water is actually using up and degrading the corrosion inhibitors.

But I understand if you disagree with that. Aside from Toyota, Honda also seems to use deionized water in their pre-mix. Some OEMs do use distilled water in their coolant pre-mix. But then again, I'm sure everything has been accounted for, chemically, and by pouring their coolant, you're maintaining the correct proportions.

For me it's just going to be Toyota SLLC so I don't have to worry about what's in it, nor its dosage.

My last Toyota was trouble-free for 9 years until I sold it, with the factory coolant still in it. I just top it off with a few milliliters of SLLC every 6 or so months if it dips below the Full line. I know I should've replaced it at year 5, but.... well, that's on me.

[Dr.Kamiya]

I'm just saying you don't need to stick with the 50% blend. That's recommended for countries where the temperatures drop below freezing. For a more tropical country like ours the mix can be as low as 30% coolant to 70% water.

Here's citation from Enilive, a company that makes lubricants for everything from Automotive to Marine to Aerospace:
What is the right water to antifreeze ratio for my car? | Enilive oilproducts


For the Nissan GTR, the owner's manual specifically instructs diluting 50-50 coolant with water in order to get to a 30-70 mix (because the engine runs hot). 50-50 is only recommended when ambient temperatures are expected to fall to below freezing:
Page 24 of this PDF: https://www.nissan-cdn.net/content/d...ner-manual.pdf


IMO instead of blindly following manufacturer recommendations, it's important to understand why those recommendations are being made, because the manuals are mostly written for their largest market (usually USA) and do not necessarily suit all other places, climates or conditions.
And as I explained in my first reply, what's really lost when coolant level goes down is the water, not the whole coolant mix because the rest of it has a higher boiling point. By topping up with 50-50, you're increasing the coolant ratio (until you get to the next full fluid flush and change). But for our local climate a lower coolant mix is actually desirable.

[oj88]

A 70/30 water to coolant mix may improve cooling efficiency but that's at the cost of less corrosion protection. Doing this may necessitate more frequent coolant change intervals. It can also potentially lower the boiling point.

Personally, unless you're maybe into frequent spirited driving or competitive motorsports, I would stay with 50/50... I've always used genuine OEM 50/50 premix on all my previous cars for top-ups... from the Honda Type 2 to Toyota SLLC. No issues whatsoever. My coolant temps on my previous 2KD and now 1GD stays at 85°C (±1°C) when hot. The Civic was both hotter and had wider coolant temp swings at around 95°C (±5°C). If there's an apparent problem with the solution being too concentrated, it was bound to show up. But all I got from doing this was a perfect cooling system.

Thanks for the excerpts. I'm not surprised that the GT-R might need better cooling efficiency.