coolant temp sensor-not where its supposed to be (?)

[Chickenhawk]

Based on the symptoms, I would go with thermostat first. When they fail, they tend to fail open and the result is coolant temps below normal over a long term. When sensors fail, they tend to read low (from being immersed in the coolant stream their whole life) but they tend to fail more erratically. If the needle is always a tick to the left when hot, I tend to think thermostat; when it's a tick to the left, but wavers a bit up and down, especially on the highway, I think sensor.

And when it wavers in a way that is not possible, such as not coming to zero on shutoff or reading at the top of the scale when first started, it is a stepper motor. Interestingly enough, I found the vehicle overspeed sensor was getting its readings from the gauge needle and not from the vehicle speed sensor. I actually got an overspeed warning when the gauge hit 195 KPH (when I was going 80 KPH) when my speedo needle stepper motor failed. I have never seen that warning light before, and it never lights up in the cluster panel light test on startup.

 

[sunliner]

everybody complains about that bottom alternator bolt, but it's easy as long as you have a ratcheting wrench. what's a major PITA for me, is getting the alternator out and back in without hitting the fan or the ac line. have to rotate it exactly right...took me forever.

 

[Mounce]

Yeah, we had to do all kinds of moves with it to get it out.

 

[sunliner]

update for anyone still following...changed the t stat out today. not even gonna say how long it took other than it was embarassing. had a case of fumble-fingers. dropped sockets x2 and lost the bottom bolt that holds the engine hoist bracket...dropped behind the alternator so I had to remove it again to find the d*** bolt. then had a case of the stupids and took forever to get the bottom radiator hose back on.

Anyway....the old t stat appeared to be in the closed position when I pulled it but must have been opening prematurely...with the new one on, gauge is dead center 210, with the scan tool indicating between 208-213 when driving. No telling how long the truck was running cool. Thanks again, all!
-Mike

 

[Mark20]

T-stats typically fail by opening too soon so when you pull them, they are in a closed position with a cold engine.

There was a show (How it's made ?) that had a segment on auto T-stats. They use a mixture of wax and powdered metals to create a pellet that expands at the desired temperature and push the T-stat open. I wouldn't be surprised if coolant works its way into the wax and screws up the calibration.

 

[blkhwkbob]

So, I wanted to update this old thread to help people out. The 2006 location might be the biggest PITA in history. I guess first you should drain down some coolant, but I didn't. I just put a pan under the car to catch what drains out. The next thing to do is disconnect the harness up on top in the back. Then I found that the best (not going to say easiest) way is to remove the passenger side tire and inner wheel well--all plastic push pins and one 10mm bolt. Jack the car way up and use a jack stand for safety, of course. Then use a long ratchet extension and a swivel to a 16mm crows foot, or flat line wrench. Once you get it loose, reach your long skinny arm up in there and unscrew it. The fun part is getting it back in there. You obviously don't want to cross thread this thing, so VERY patiently reach your long skinny arm all the way up there and start it by finger. It should screw in several turns by finger. Tighten it up with your 16 mm crows foot and put it all back together. Add coolant as needed. Hope you never have to do this job again.

Bob

 

[Mooseman]

So, I wanted to update this old thread to help people out.

Old is right! Good info though only if you have skinny arms