Quote Originally Posted by geezer101 View Post
Is it because there's cold coolant above the thermostat acting like a thermal heat sink on the thermostat itself? The coolant below it is reaching operating temperature which the gauge sender is reading correctly. A theory...
That makes sense, because if the truck has been sitting for long enough that the temp is near the bottom of the gauge, it will get up to operating and stay there without the temp spike. Enough heat surrounding the thermostat that it does it's normal thing.
Pennyman, do you have a link to one of these reverse flow thermostats? Next time I replace mine I think i'll go that route.
And Junker, A new fuel pump might have an effect on your lean spots. The Weber's are pretty sensitive to fuel pressure and adequate flow. Maybe the pump is getting weak on you once you have some under hood heat on the highway?