Water Temp Sensing Unit
The sensing unit is located on the top of the rear of the generator when you stand looking from the front of the rig to the rear.
To access the sending unit, you must remove the top panel of the generator set. The top isn't hard to remove - a bunch of 10mm bolts - if the generator is on a slide or has access. I'm not sure about generators that are bolted in-place in the front of the rig.
The first pic below is of the sensor itself; the second is a picture of the location after the top panel has been removed....you can see where someone has taken a photo of a drill bit making a hole in the fairing/cover. The white wire goes to the tip of the sensor, and in the photo the thermostat has been removed.
In order to access the sensor to remove it, I made a big hole in the fairing/cover to allow access straight over it using a socket and a short extension. The space is very tight and the sensors are usually a bear to remove with just a wrench from the side.
I soaked the sensor on ours for 3 days with PB Blaster, then heated it with an electric heat gun (didn't have a propane torch). Immediately after heating, I oh-so-slightly turned the sensor clockwise as if to tighten, just until I felt it begin to move. Then, reverse direction of ratchet counterclockwise to remove and it came right out.
When replacing, I did put a small dab of non-seize on the new one before snugging it down.
Most folks recommend checking and possibly replacing all hoses while you are in there. I also replaced the thermostat and gasket.
After replacing the sensor and before buttoning everything up, I used two layers of alumimum ductwork tape to cover the hole that I made, facing several pieces sticky side in. Air flow is critical to the generator, and I made sure to put several layers and ensure that there was a good seal all the way around.
I hope this helps.....there are a lot of threads on replacement of the sensor if you search here on irv2 for onan overheating.
2004 Newmar Mountain Aire 4301 DP
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Towing 2006 Honda CR-V