I don't recall the RMR30 having an electric fan for the radiator, only the A/C...
If so, I suggest you check the temperature of the radiator vs the lower thermostat housing - if there is a large difference, then you could have a jammed thermostat.
Or, all other potential cooling system issues aside, the gauge sensor could be crook. They are only around $20 from memory, but can be a bugger to remove due to corrosion.