I think your referring to a cooling system additive that reduced the waters surface tension and probably adds a lubricant primarily for the water pump's bushing and seal. IMO little or no benefit. And you really _don't_ want to "improve" the heat transfer efficiency across the radiator anyways.
Earlier this week I just did the cooling system "change" @60K miles (the "severe" schedule). Maybe a waste but I do recycle so its not dumped into a river somewhere. Like many Honda models there is an air "bleed" screw on top of the thermostat housing. Being in somewhat of a hurry I failed to:
1) Bleed the air.
2) Cycle the engine to "hot" to verify thermostat and fan operation (didn't want to waste the gas

).
3) Closely monitor my gauge for any warnings of the above.

:!:
My commute home is almost 25 miles and I did not check the gauge until 1/2 way home :shock: I was reading 8 bars :!: :!: :!: Nor could I get any heat from the heater. Almost certainly the dreaded thermostat "air" lock :!: And I have my 6x17 radiator block installed too :shock: Thankfully it was a cool day, upper 50F. Being overconfident I immediately changed driving patterns to P&G (Pulse & Glide) as a heat limiting style only :!:

(overall MPG with P&G was an atrocious 72 ish since I depleted the IMA SoC and was in forced charge much of the way home).
Apparently this was sufficient in that during the glide periods the gauge would usually drop back to the normal 6 bars. Upon arriving at the house I immediately opened the hood and felt the engine and sniffed the oil for any indications of an overheat. NONE :!: <whew> In fact the engine was its normal 200F ish. A reflection of the high thermal efficiency of the engine (fuel to mechanical force with less loss to wast heat in the cooling system. Read: high MPG). Topping of the cooling system only required 1-2 cups of additional coolant further confirming an "air" lock situation.
On my commute the following day MPG's were nominal (after replenishing IMA SoC due to the
[email protected]#^* P&G driving). But apparently no damage has been done.
So the moral of the story is:
1) The Insight needs _NO_ help to run cooler. In fact its been shown by the radiator blocking technique that it needs lower cooling "efficiency".
2) _Always_ air bleed the cooling system after changing the coolant.
3) A bit of wasted gas may save an engine :!:
4) Thank goodness for P&G and cool temps :!:
HTH!
