Tried it once but could`nt see much benefit - IMO the money is better spent fitting a dash mounted fan overide switch so you can kick the fan in early when approaching traffic or citys etc. and prevent heat soak
I haven't used it in my wedge but did in my TR7 V8 which ran very hot in summer. Found it did seem to help to control the temp and kept it slightly cooler than just water/coolant. Dash override for the fans is a must though....
