89 f150 4.9 six......temp gauge is jumping around from normal-cold to just under normal middle....stays at normal-cold then jumps back up to just under normal-middle....faulty sender??gauge? truck is not running hot or low on coolant.....

 

When my last 4.9 did that, the wire connector was loose. I took a pair of pliers and crimped the end a bit tighter and remedied the prob. Also, it only costs about $5 to replace the sender.

Hope this helps....

 

Is it moving quickly or is it a gradual movement? Quickly could be an electrical issue, ground or faulty sender. Gradual may be your thermostat acting up.

 

it moves quick....it never goes above the normal temp range that it ran at before the gauge started actin up