Just converted my 89 Renix to an open cooling system. New radiator, hoses, cap (16psi), coolant bottle, and thermostat. Previously, my jeep would run around 210 and creep up on the highway to maybe 220, and REALLY warm up when going up long hills. Now, it seems to run around 215, just above the 210 mark on the gauge. On the freeway when pushing it, it creeps to around 225. Haven't done any long hills yet. I would like for it to run just below the 210, or on it. I have an engine monitor which reads the computer and it says the water temp is 195 degrees when its all warmed up, yet the dash gauge is different saying 215-225. I'm aware it's a different sensor/sending unit. Any suggestions?

Update: inspected the temp sending unit. The elbow connector slid off very easily. I tightened it up as best I could so it doesn't slide on-and-off so easy. Also, the wire isn't in the best shape. Could this cause the temp to read incorrectly?

 

Yes a bad connection could cause a false reading. The best way to check is with an IR temp gun and check the thermostat housing. Is your fan clutch working that could cause the temp rising on the highway and make sure your fan shroud is in place too.