Thermo or water pump?

I would personally hold off on the Watter Wetter. What Watter Wetter does is allow the block to transfer heat to the water more efficiently, so the metal in the engine will (in theory) run cooler BUT the coolant temperature will be higher. Here's a more lengthy explanation:

When the coolant runs by the cylinders (or any hot part of the block), the coolant BOILS in a thin layer due to the heat differential. Note not all the coolant boils, just the part right up against the metal. Heat is transferred to the coolant through the bubbles in the boiling coolant, cooling the block. This is how any liquid-cooled engine works.

If you could reduce the size of the bubbles in the boiling coolant, you can get the non-boiling coolant closer to the metal and transfer more heat into the coolant. This is what Water Wetter does. In a cooling system that is working well AND has more cooling capacity than the engine needs, Water Wetter *can* lower the operating temperature by transferring more heat out of the block and keep the metal cooler. The coolant won't heat up as much, so your temp gauge won't go as high.

Remember, any engine will overheat in minutes without any coolant. The coolant system keeps the engine running cool enough to keep operating. Now, if your coolant system isn't able to disperse enough heat and is running too warm, the system isn't working right. All Watter Wetter will do in this case is cause your temp gauge to rise faster, although your block should theoretically be a bit cooler than before.

In my opinion, if Water Wetter "fixes" a cooling problem, then it's only masking the problem rather than fixing it. I'd rather dig farther into the problem and find out the real cause of the overheating.

I could see a use for Water Wetter on a modified engine, if you want it running as cool as possible. But on a stock engine? I'd rather spend the money on something else.