I've tried the cap removal when hot now - no change. Next up I've got a capillary adjustable thermo-switch and 2 slimline 6" rad fans.
The plan is to have a activation switch inside the car to enable the aux fans, then the thermo-switch to actually turn the fans on / off.
Position of the fans is planned to be underneath the 2 triangular mesh covered vents to the side of the headlamp cowls. When on they will blow hot air out. The only other slight concern I have is that the fans don't "windmill" excessively in normal driving. We will see ..........
