Hi,
Is the fan clutch kicking in? It will make the fan roar and make about double the normal noise. THis is normal on a mountain grade, but should bot be coming on while driving around the block, your engine should reach the middle point after about 4 - 6 miles driving, and stay there until you climb a mountain.
So if you never hear the fan clutch kicking in, I vote to replace it. Your actual problem is the thermostat is only opening about 65%, a little of the wax has leaked out. Get one at your local Napa store, or other local auto parts dealer. It only takes about a hour to replace it, you first need to drain and capture the coolant, only need to drain about 1/2 of it, or about 2 gallons. The thermostat housing is the upper coolant hose, and it blocks all the coolant flow until thermostat gets hot, then the small amount of wax inside expands, opening up the water flow to the radiator.
Anyway the housing comes off pretty easy, and should be an easy fix.
The fan and it's thermostatic clutch is a bit more difficult to change. Sure there is plenty of room under the RV, but you will be on your back, and the front axle is directly under the fan, so getting to the bolts is a bit difficult.
You might also need to wash the radiator. They do get dirty, and taking a garden hose to it will clean it up pretty well.
Fred.
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