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Just found this old thread and thought I'd add a little more info on my last post for you potential Locost rotorheads. I raised the fan temp control in the Megasquirt to come on at 195 deg and go off at 188 so fan cycling at idle is reduced. At the previous setpoint, I was trying to cool the radiator before the cooling thermostat was fully open. Both the fan and thermosat were competing for the same control range. I have now done over 2000 street miles this summer with highway driving constituting > 70% of that. I don't know what I did right, but I have zero cooling issues. I have no temperature issues while driving extended periods at 70-75 MPH in 95 degree weather or at low speed in-town driving. In both cases, I come to a stop and within about a minute, the fan comes on, then goes off as it reaches the lower temp limit just as it should. This is with the same Civic radiator as mentioned before and no body modifications.

One thing I did notice is that at speed, the bonnet is normally sucked down tight to the scuttle, indicating a low pressure in the engine compartment. I interpret this as the incoming cooing air has plenty of areas to escape. If it didn't, a pressure buildup would occur in the engine compartment and I'd see a slight gap along the trailing edge of the bonnet.

I was expecting I might have to revisit the radiator size/construction and/or add some ventilation to the side panels or bonnet. It appears that I will not have to make this modification. I suspect my success may have something to do with the slightly oversized fan operateing in a pulling mode and the S5 oil cooler being directly downstream of the fan, at least for the intown driving portion.

Mind you, my car is a street driven Locost and not used on the track.