Greetings again,

In the previous post, I labeled the ports on my radiator, and now I'm confusing myself :-)

When I was talking to Bruce about my oil temp issues, he suggested that I run the (currently plugged) heater output into the radiator inlet to produce some more coolant flow through the radiator.  This would be in an effort to increase the efficiency of the oil/water heat exchangers when the thermostat is closed, and there's little water flow.  If I prove that I need to lower my temps, I'll try this.  Certainly, water will actually flow from the heater port to the radiator inlet tank, because Bruce said Mazda used to do this with the 1st gen oil/water heat exchangers. 

Since water will flow from the engine to the radiator inlet tank, why do they return the heater itself to the radiator outlet side.  This is also true for the AST, and turbo as far as I can tell.  I certainly plumbed my AST and turbo returns back to the radiator outlet tank, so in effect, they bypass the radiator.  The volume of water is small, so it's probably not a big deal, but it just seems odd that they wouldn't return all the water to the same place.  I initially thought that maybe they made an exception for the oil/water heat exchanger return, since it would be picking up heat, and they'd want to pass that through the radiator.  Of course you'd think the same would be true of the turbo water return.  

Rusty;

The pressure differential driving the water from the engine block heater outlet to the rad inlet is the pressure drop from half way through the engine to the rad inlet.  Although this is enough to cause some flow; it is likely quite a bit less than the pressure drop across the rad.  By returning the heater flow downstream from the rad, you take advantage of the larger pressure drop and get more flow through the heater.  Or is this stuff you already know, and I missed the point here?

One of the difficulties with the oil-water heat exchanger built into the radiator is that they are designed for piston engines where the heating of the oil is more incidental; it is not one of the cooling fluids as it is in the rotary, so the heat rejection capacity is significantly less. 

Al