Subaru4you - Water Wetter, for Cylinder Head Hot Spots

WaterWetter® is a unique wetting agent for cooling systems. This liquid product can be used to provide rust and corrosion protection in plain water for racing engines antifreeze to improve the heat transfer of ethylene and propylene glycol systems. Designed for modern aluminum, cast iron, copper, brass and bronze systems.

Increases the wetting ability of water
Improves heat transfer
Reduces cylinder head hotspots
Reduces rust, corrosion and electrolysis
Provides long term corrosion protection
Cleans and lubricates water pump seals
Prevents foaming
Reduces cavitation corrosion
Complexes with hard water to reduce scale.

"Water Wetter" is designed to reduce hot spots in your cylinder head. It does this by reducing the build-up of water vapor in any superheated areas. The bad thing about having hot spots in your cylinder head (combustion chamber) is that they can promote pre-ignition - definitely a bad thing. This harks back to Smokey Yunick's theory of "soft combustion chambers". Any sharp edges in your combustion chamber (around valve seats for example) may tend to get very hot (even red hot) during operation. These areas of the combustion chamber can then form local hot spots in the cooling passages. Thus, even though your bulk coolant temperature is well below its boiling point (i.e. your gauge reads just fine), there may be localized boiling in some regions of the coolant tract.
This localized boiling can cause a layer of water vapour to form over the hot spot. This vapour forms an insulative blanket and prevents heat from leaving this area thus making the hot spot even worse. But reducing the surface tension of the water with water wetter makes it easier for vapour bubbles to leave the surface of the cylinder head and allows the bubbles to convect heat away from the area.(info) http://www.water_wetter.htm

Water Wetter £10.75