I'm having my car reassembled after big bodyshell rebuild some of you have followed for some time now on Escort Cosworth forum. It already runs and dries but there is some strange cooling system problem and we're basically out of ideas for now. Whole system have been dissasembled and now assembled , filled with coolant, bled and seems to work fine, temperature is where it should be when stationary or driving at mild loads. The problem is when you rev the engine just a bit loud noise similar of water pouring into a bathtub can be heard in the heater and as soon as it goes on boost the temperature starts rasing rapidly. It is like the system was not properly bled, but I have no ideas why it would be so. The thermostat seems to work just fine, as well as water pump with is almost new anyway. Any ideas or suggestions?

It's only major mechanical problem that stops the car from being back on road.