C15 - water temp erratic - what could it be?

Just got my truck back from an inframe. It runs better than ever before the only thing is, my water temp is acting strange... On flats where the temp would normally run 188* it will just randomly go from 188* up to 194* and bounce down to 186* then up to 192* over the course of a minute or so, for no good reason. It used to hold steady at any given temp, and any rise in temp was predictable on hills, steep grades, etc. And for some reason I can turn the fan on and it will never pull down to 186* like it used to always do. For whatever reason the fan will only pull it down to 192*. These temps are from CAT information display. My regular gauge in the dash the needle shows to be a little bit hotter than the 180* mark where it used to always sit and again the fan won't pull that down to 180*.

Don't have a digital readout of oil temp on CAT ID but on the gauge my oil temp normally always rode at "180*" The oil temp will hold steady there for the most part but sometimes in hills I notice it appears to rise about 5 or maybe 10*, not very much at all (not enough to really bother me a whole lot) and the only way to get that back down to 180 is with the engine fan. This is also "out of the norm" for my engine but I figure as long as oil temp is well below 200* it's nothing to worry about. I trust my oil temp gauge is failry accurate - at the very least it's not erratic. The water temp is driving me crazy even though I don't think it is running hot. And I also don't believe the actual coolant temp inside the motor is really erratic like the gauge is showing. Is it a sending unit that tells what the water temp is? Where is that at and how can I check it? Other than this everything is good with the inframe I'm really pleased with it.

 

I sort of figured the tighter tolerances could be a possible/logical explanation on the oil temp. Since it's not erratic and not TOO high I am ok with it..

They did put a brand new water pump on it - so I'm guessing they also put new stats in as well - CAT did the inframe.. Like I say it does this in the flats when I'm not really accellorating and maybe cruising along at 10psi boost or so. It will sometimes hold steady at 192* for a little while and then for no reason bump up to 194*. It might stay there for a little while or it might bounce down to 188* then 192* or whatever. It never holds constant for long and there seems to be no reason for it based on how I know my motor used to behave...

 

Ok, where are the senders located? I suspected maybe the connections might be loose but don't know where they are. And Oscar you are correct there are two temp sensors, 1 for CAT info display, and a separate 1 for the gauge. I remember some general conversation about different things, water temps was one thing discussed - how accurate was the gauge versus CAT ID - and was told they have separate sensors. Now where exactly they are, I wish I had asked lol. Thanks guys, hopefully it's something simple. One more thing, pretty sure most if not all of the air is purged out, I'll check the water here shortly, but it's got 13 gallons in the system. Thanks for the tips..