Hey Guys,
I've got a F250 with a 351 in it. It's new to me, and a great truck. However, I noticed the temp gauge going back and forth slightly (between the inner o) and the M. It never overheats or anything. Is this something to worry about? Does it at highway speed and sitting around in the drive too. It's not a huge variation either way, just a tic of the gauge either way. 155K on the clock.

 

Probably not anything to worry too much about. But might be showing signs of a weak Thermostat. If it hasn't been changed recently then a good flush and new T stat...should set you good for the winter. or a iffy temp sending unit.

Are you loosing any coolant?

 

if your mileage gets really poor this winter that would also point to a weak tstat