Okay, I decided to do a test run (garden hose water) before I cycle the citric acid. Me Smart .

It is 10°C (50°F) today. The truck does reach operating temperature. The heater core hose (with the Tee) is hot, the top of the thermostat is hot but by the time the water pours into the rad it is cooled off. I had the grill blocked but the radiator and fan is still way too effective.

The temperature of the water coming out the top of the rad is cool. This is not the time of year to do a hot flush with citric acid. With thermostat in, I can't be positive that the rad is thoroughly flushed of acid and with thermostat out, I don't think that an effective temperature would be reached to have the acid do its job.

I have only read that the acid needs the high temperatures to work effectively. Chemists (or those who know) correct this if it is incorrect.

One thing - we need a properly operating thermostat. It can't be good for the engine to be running during the winter with an open thermostat.

I am going to start another thread on this. I want to include a citric flush and steps for doing this with the original thermostat (or not having to remove modified thermostat). Look for Coolant Flush (round 2).