Why does the heat gauge on my 1994 f 150 climb to almost halfway and then drop back down to cold in then repeat the process as I drive. it never use to do this it would always climb to be just between cold and hot and stay there

 

its probably the sensor going bad

 

x2 mine did the same thing till i replaced the sensor.

 

Where is it located, what's it do, what's it called

 

Check your coolant level too, low coolant makes this happen a lot.

The sender is a single wire unit on the intake manifold. The wire going to it is red with a white stripe if I remember correctly. the wire connector just pulls straight off. Tell me what kind of engine you have and I may be able to find a picture.

Do not replace the 2 wire sensor on the coolant pipe. This sensor goes to the ECM and does not play into temp indication.

 

Depends on the engine. On my 4.9 its located on the back of the cylinder head on the pass side, near the fire wall.
regards
rikard

 

Here's the location on the 5.0 / 5.8 motors. The vantage point is stupid but there ya go. It's as if your face is right in front of the brake booster looking at the dist... weird...

from http://autorepair.about.com/library/...bl432a-lib.htm

 

Is it not possible that it is my water pump. What does that sound like when going out.

 

you will get a humm if bearings are going bad but most cases they just leak from weep hole or front seal