Open loop for 'insufficient temperature' at 190 degrees. How?

[stomper]

I have a 2000 4.8 in my 73 P10. I'm chasing some codes which are probably related to the oxygen sensors. However first order of business was putting in a thermostat where there wasn't one before. I still get an open loop error because of insufficient temperature which I was assumed because I rarely got over a hundred and sixty degrees with no thermostat in there. Now it's coming up to temperature but still won't go into closed loop. Prior to putting in a thermostat it would occasionally go into closed loop but ran like crap probably because of the oxygen sensors and then it would go back into open loop because of system failure. Any ideas on the temperature issue?