Water Wetter won't change the reading on your temperature guage because it doesn't change the temperature at which the thermostat opens when everything is working properly. What it does do is increase the heat transfer capability of the coolant, so that the metal stays cooler than it would at the same guage temperature without the stuff. However, as someone else mentioned, it isn't as effective in a 50/50 mix as it is in plain water, which is unfortunate because the heat transfer capabilities of 50/50 ethylene glycol and water are not as good as plain water (another reason racers often use plain water rather than anti-freeze blend, in spite of the latter's much higher boiling point).