What are heat exchangers?

[smshirk]

Originally Posted by mikstew

A heat exchanger is a device used to transfer sensible heat from one fluid to another by means of convective heat transfer. There are many different implementations but the most common is metal tube and fin, the purpose of which is to maximize the surface area upon which both fluids make contact. In automotive applications this is typically done with a gas (air) on the shell (external) side, and a liquid on the internal side (coolant for your heater, CFCs for your air conditioner).

As a chemical engineer I had to answer this one

Two possible reasons why you are overheating: debris is causing a blockage, or you have air the system. One is a lot easier to fix. Air is a ****************ty heat transfer fluid and thus will not keep your car cool (hence why we all switched to water cooled engines in the late 80s). Also note that the symptoms of both are the same. In other words if your heater is blowing cold when your car is hot, you do not necessarily have air in the system, it could still be a blockage.

Let the car cool. Take off rad cap and start the car, allow to run for 30 sec, add more coolant while running. This will help displace any trapped air. Also someone said there is an air bleeder valve in the system, use that, itll help. As someone else suggested, be careful about running too long. The thermostat will only measure temps in one location, while you may be boiling off coolant at or near the cylinders (which would be VERY bad)

Even though I love the Boxster and the 996 I had, I still wish Porsche had stuck with the aircooled engines. They finally solved the AC issues with the 964 and 993, and the 993 was darn near perfect, top end issues notwithstanding. In addition the aircooled engines were hand assembled and made to last forever. Our M96 engines just aren't as good with Porsche going mass production. The upside of that is more folks can drive Porsches and they are immensely more comfortable as daily drivers, but the sound and fury of an aircooled engine especially still calls those of us who started out with VW's and moved up to Porsches as we got older and had more money. It's true they run 20-30 degrees hotter than water pumpers, but the engines were no worse the wear for it. Even stuck in rush hour traffic in deep south summers, my 911 handles the heat much better than I do without real AC. It now sits all summer and is mostly a late fall early spring car, but I can't bring myself to part with it.