My baja bug has a 2.5 litre turbocharged subaru. When I built the car I mounted the radiator in the rear above the motor (see picture). I also mounted two electric fans. The problem is when I an moving fast the car will overheat, At speeds slower than 30mph i have no heating problem. I tried building a intake cowl , i tried reversing the fans but nothing seems to help. The radiator is aluminum and way oversized for a 4 cylinder. The only thing I can think of is the shape of the bug is creating a vacumn at higher speeds.

Any ideas??

check your timing. If you are advanced, you'll run hotter. Also ensure you have good fuel flow to the engine. You say you reversed the fans, so that almost ensures that it isn't a vacuum issue with the body shape right? Check for proper operation of the T-stat.

I imagine you have checked to ensure your radiator is free of any trapped air. Have you ensured your intake was burped of any air? I believe there is a high point on the intake cross over.

Jay

You probably have air in the cooling system. Make sure you are using a factory Subi thermostat with the vent hole up.