On my setup I use a 3d table to PWM an engine water pump. After a lot of testing I found using the temp output from the radiator and ECT the best way to control the pump. Takes into account out side temp and vechile speed. Would recommend you try that way to control the thermostat. Ive also connected a 2nd Digital output to the same soild state relay as an override. So if I'm at a set TPS or boost range the pump goes to 100%. After a bit of testing during different conditions I can keep the ECT within 2deg in all situations.
