Replace the radiator. Add "Asian Blue" coolant. Burp the system properly. Done.
Skip the step where you add magic snake oil.
Completely agree here. What is likely killing engines (which we are NOT really hearing about) is not the manufacturer's recommended coolant, is not cooling capability, but coolant loss, caused by never checking the coolant and not knowing what to look for when you do.
With so many ways for a small leak to develop in these old cars, and with the temperature gauge not effectively warning of an air-in-head condition, checking the coolant level at every fillup is probably the best way to avoid an expensive failure caused by loss of coolant.
It's simple: put a piece of tape on the coolant reservoir tank near the driver headlight (LHD cars). Start with filling the tank to the L level if it has cold soaked or to the H level if the engine is hot and running. Get the car hot by driving it and without turning off the engine, read the high coolant mark on the tank; mark it on the tape. Then, after an overnight cold soak, mark the low level. At every fillup, check to level; it should remain at the H mark or quite close. Every once in a while, check the L level when the engine is cold. If the coolant ever goes above the H or below the L level, sort it out; check the Service Manual, and read or post here for tips.
I have a piece of tape where I can prominently see it when I open the fuel door that reminds me to "CHECK OIL AND COOLANT". I do this religiously at every fill-up, because I know that the time I don't is the time that the leak develops.
The coolant recovery reservoir is an essential component of the cooling system. I'll repeat that: it's an essential component of the cooling system. Since the cooling system is sealed, increases in temperature can lead to tremendous increases in pressure without a way to relieve that pressure. A pressure relief valve in the radiator cap allows this by allowing coolant to flow into the reservoir as the car heats. When the car cools, the drop in pressure sucks the coolant back into the engine.
Another known failure is the black tube falling into the coolant recovery tank. This needs to be secured. It is VERY important that this tube makes a tight seal around the tube on the tank cap. If not, then when the engine cools, instead of sucking coolant back in through this straw, it will suck air in through this "crack" in the straw.
Some of us suspect that low coolant isn't enough to raise the temperature gauge significantly but is enough to make the cam bearings run hotter (due to air in the head) leading to cam seizure. At a minimum it is likely contributing to overheats and cylinder head warping or gasket damage. @Bull Dog
is in a far better position to speak about this than I am. I have only dealt with two cars that were exhibiting cooling system issues.
I hope this is helpful. It seems that the use of the "wetter" arose from track rules that prevent the use of antifreeze so as not to contaminate the track's surface, and is not an improvement to existing cars. The antifreeze that Honda specified has additives to protect the engine internals from corrosion. Unless one is willing to perform the long term, thorough electrochemical testing that took place when the cooling system was designed, I would not deviate from the Honda recommendations.
If one has actually instrumented the cooling system to monitor temperatures in extreme environments (ie, climbing out of Death Valley during the hottest days) and the small margin of additional cooling capacity is warranted, one should first check the obvious: is the temperature actually lower in normal conditions too or is the thermostat staying closed? Are the radiator fins corroded to the point where their cooling capacity is reached before the hottest environmental conditions are reached? (@Bull Dog
recently posted about this as well.)
The decision to change something like coolant, oil, transmission fluid, etc from that recommended should be evidence-based, and sometimes the salesfolk don't want you to collect that evidence, because you might find that their product is warranted only in a situation that you'll never encounter (like taking your daily driver to the track).