ACCERT sensor location

It's on the bottom of the thermostat housing on the right side of the engine.

 

facing the front of the truck, kinda hard to get to unless you have small hands! if its only showing 125, turn your heater on and see if its getting hot or just warm, you may have thermostats stuck open causing it to run too cool, the acerts were bad about that once they got some miles on them, just my.02

 

I've driven several that would only run 145 on flat groung pulling a load. That's water and oil. They would hit around 200 on a hard pull, and down to 130 on the downhill. Was always thermostats.

 

There are 2 thermostats on the ACERTS. Both of them are located in a housing on the passenger side top front of the motor (same housing as the coolant temp sensor if I remember right). They are not hard to replace, just make sure you get new o-rings with the stats since reusing the old ones could cause coolant to bypass resulting in low coolant temps. For future referance...the ACERTs don't have oil temp sensors. The oil temp reading is the ECMs best guess when it compares the coolant temp and air temp. This is why both of your temps are so close even in the cold.

 

as pulling trucker said, the housing on the upper right side of the engine, same housing the upper rad hose connects to, both are in there. make sure you get 2 t-stat's, 2 seals that the t-stat sits into inside the housing, a gasket for the 2 halves, and a gasket for the housing to head. there are 3 bolts that hold it onto the head, you will have to swing the alternator out of the way to get to at least 1 if not of the bolts. drain coolant, remove alt, upper rad hose, more than likely depending on the truck the upper rad support bar, loosen the little clamp at the little hose on the bottom of the housing take out the 3 bolts that are kinda center and form a triangle on the housing, take a pry bar and break the housing free, finagle it out of the hole, take the rest of the bolts out and lightly tap around the housing and it should break into 2 pieces. the rest is pretty self explanatory. some good gasket remover and a scraper should take care of cleaning the surfaces. and reassemble, should take about 3-4 hrs with hand tools or less if you have airtools. some mechanical knowledge is required, not being a smartbutt but if your not mecahnically inclined I wouldnt attempt it. I am a former diesel mechanic so I could do it in about 2hrs just for info sake you should be able to do it in 4hrs with hand tools. just my .02 hope this helps.