Random difficult start engine when the car is warm

I recently find the coolant overheat again, what I find the gauge read about 64-68 °C, but the OBDII read is 88°C, so even if the coolant got boiling, the fan not running normally, some super one can tell me, how many temperature sensor in this type car, why the gauge not following the correct temperature and the fans can't turn on in correct degree? I guess I should change cable first, please give some good idea before I waster time again?

It looks superman still not see my post :), I add some new situation for this issue: Now, I know there are two temperature sensor in this car, OBD temperature close to thermostat in engine bottom, the second temperature sensor in the blood housing room(top of the Coolant system). After I change the blood housing again, it looks the issue is same, I confirm the fan start in correct point about 90°C(gauge reading) and it can control the temperature and keep stable. but when it run for 20~30 minutes, the gauge always in 90~95°C, but the OBD temperature is stay in about 105~115, it means in part of engine, the coolant maybe boiling , so my coolant will boiling to coolant reserves, when the car running in this temperature, I stop the can, turn off the engine, start it, it can start no problem, but if I stop the engine for 5~30 minutes, the gauge stay about 80~85°C, the OBD temperature reading in 95~105°C, the engine can't start, should press the accelerator to keep the engine running, and the engine warning light can show in dashboard, it read some engine failed working, keep this for one minute, the engine run as normal... Why the two temperature has about 20 degree difference? and the engine running like this?