Then again in Eastern Washington the same overheating occurred at the top of another pass on this very hot day. However this time a mile before the summit the temperature gauge surprisingly dropped from the ¾ mark back to exactly midrange yet we were still climbing.
This indicated to me that likely the electric fans for the radiator did not turn on until late. We were able to get to Boardman Marina RV campground without further overheating. The next day I stopped at NAPA auto parts and picked up a temperature switch to use if needed. We planned to return down the Colombia River to Portland and then back home using I5 which has no passes to climb.
After studying the clumsy wiring diagram I determined the temperature switch they sold me was not a switch but an analog sensor which likely would not cause this fault. I tried to return the switch at the Poulsbo NAPA but they were not associated with the Boardman City NAPA and could not allow a return. I did purchase and installed a solid state relay which is located under the drivers side headlight for $65. I turned on the air conditioner and verified the fans kicked on after several minutes. Hopefully problem is solved.
The Caravan fan circuit measures the temperature from the temperature sender which goes to the gauge and the computer. Then the computer determines when the electric radiator fans trip on and energize the solid state relay which energize the fans. This was a common problem as revealed on you tube which showed how to replace the solid state relay.