High water temp???

wash the bugs and dust out from the engine side toward the front. you'll be AMAZED by how much crap comes out...

 

Yah, sorry. Like Bulldoggin said, I meant to wash out the rad for dirt and bugs. Sometimes the air to air has to come out to gain access. We just use a pressure washer and try to spray straight on through the cooling fins.

 

On a 3406E the fan doesn't kick on until 217 degrees, high water temp warning buzzer goes off at 228 degrees. This is a factory setting and can't be changed. I noticed mine was running a little warmer than usual this last week as well. I'm going to change the thermostats and see if that helps. I already cleaned the bugs and grime out of the front of the radiator. You can pull of the A/C condenser and the charge air cooler and spray them all out separately, that helps get them cleaner.

Your manual gauge can actually read =/- 10 degrees. If you want to see what the ECM sees, get a Scangauge D. You can get one for around $180 at an RV store or order online. It plugs in to your ECM and shows you what it is reading while going down the road.

 

if the dash gauge was faulty. i.mo. that would not set off the engine warning lights or derate. whatever is making the dash gauge eractic is the cause, cannot be the gauge itself.