Which t-stat to use.

[acloco]

....and the ECM barely gets into closed loop...so ALWAYS running on the rich side of the engine management block.

Keep your t-stats in the 195 range. If you are having problems keeping the engine cool, then you have other problems in your cooling system.

First item I would recommend - removing the inefficient engine driven fan and replace with a thermostat controlled single or dual electric fan.

Second - replace your radiator with a new, aftermarket, aluminum, high efficiency.

Third - use distilled water in your cooling system.

Fourth - use a water wetting agent - you might be surprised.

5th - aftermarket aluminum or steel higher efficiency water pump.