Dave,
An electronic timer that you can buy (or build yourself if your handy) set to keep the fan/pump running for "X" amount of time after you switch off the ignition will solve that problem
Any electronic part stores down under? Couldn't cost but a few bucks to roll your own. I have one that I built that keeps the two-way radio on for 15 minutes after I turn off the car. If you want to try, let me know your address via e-mail and I'll send you a drawing.
- Jim -