I've tried water wetter, and it does drop the temp. Just poured it in a 50/50 mix, and within minutes saw the temp gauge drop ten degrees. It stayed ten degrees cooler under most conditions after that.
It did nothing to prevent an overheating issue caused by the e-fan not turning on. Most overheat issues are a lack of airflow thru the core - and overheating is the direct result. Regardless of what I thought was working correctly, it still boiled down to no air, no cooling.
Once I fixed that, the longer term result was less satisfactory. Because of the overheating, the head gasket was weakened, and that led to the coolant - being wetter - creeping thru some warpage more easily and voila, dumping into the crankcase. BUT - you couldn't see
antifreeze in the
oil. That's because water wetter allows stuff to mix thoroughly. I changed the
oil three times to stop a lifter collapse problem when it finally occurred to me that the engine had consumed two gallons of
antifreeze mix - but I had never seen any evidence of it I could recognize, until I realized I was pulling 9 quart
oil changes.
If you're having overheat issues, water wetter isn't the answer. Fixing the lack of heat transfer is. The typical causes with the radiator are air bypassing the fan and/or not going thru the core, usually caused by no shroud or no fan. With coolant, the core itself is clogged, the t-stat fails shut, the water pump impeller isn't working, or working far too well.
"I knew for a fact" the coolant temp sensor couldn't be the problem - until I learned it was just exactly that, a temp sensor - not a fan switch. Temp sensors won't pull 12VDC and engage a relay, they send about 8-9VDC at 195. Fail. Don't "know" your part is working correctly, test it and be sure, especially when the previous attempts have failed. That's direct evidence an assumption is false and you're wandering in the rose garden.