I need a water pump capable of about 2-3 litres per minute at a somewhat modest pressure for pumping water through a WTA intercooler then through the heat exchanger at the front.

I've tried various pumps not intended for the job like aquarium pumps, windscreen washer pumps and had no luck - while they can happily pump water at their rated amount (eg 1000L/hour/1meter), they can't cope if there's a tight restriction as all the copper piping is. If I connect a hose from the tap, it flows through easily, if you turn it to maximum it flows through s**t more than I need.

What is available and whats the cost?