For the past few days, my water temperature gauge has been fluctuating slowly between the N and the lower bracket of the normal range while I am driving. Normally, when I start my truck cold, the needle slowly climbs up to about the M in NORMAL, then immediately drops down to the N and stays there for the remainder of my trip. However, this is no longer the case. After its decent to the N, it will eventually drop further down to about half way between the N and the lower bracket, and then climb up to the N when I am at a stop light, then back down when I am cruising on the freeway. I am not too worried since the needle is not indicating a warmer temperature, but something must be causing this and I want to make sure this isn't going to cause problems further down the road. As always, any help or info. would be greatly appreciated!

 

The gauge sender is different from the ECT sensor which feeds temperature data to the PCM. A malfunctioning sender will have no effect on anything except the gauge reading. It's worth fixing just to have it right but it's not critical.

 

Ya my gauge just got a mind of it's own now too...before it used to normally ride at about the N...but after a cooling booboo and I fixed it it now normally rides at the A, I even checked the temp with a laser thermometer and it's running at perfect temperature, so I pay no attention to the gauge now.

BTW- I replaced the gauge temp sending unit the other day...it was like $4 from AutoZone.

here's my post:
https://www.f150online.com/forums/sh...hreadid=127686

 

An air pocket around the temp sensor will cause the gauge to be more reactive.