How did they coolant look when you flushed it out?. You could have a blockage somewhere. At highway speeds does the temp. stay the same?

 

I didn't flush it out. I just filled it up with fresh coolant and water. When the coolant started to move, it looked like a milky yellow color. Maybe I should try flushing it out and starting over. At highway speeds, the temp stays too cool. I just can't figure out why it would stay too cool too long. The other day it got up to 190ish, but that was after a long while of driving, stopping, and starting.

 

^ if the thermostat is working properly, and the outside temperature is normal (32-100 F), then the engine temp should come up to normal (180-195) within about 5-10 minutes of driving. if it doesn't, you tstat is bad.

FailSafe brand is notorious for .......failing.......

The Stant SuperStat is the best. about $15.