The car: 74 Challenger, 318 with mild upgrade and freshened up ('69 block), 340/360 cam from Comp, NON-hp AVS, dual exhaust thru late model Magnum manifolds.

The sit-rep: Only driven short periods (less than 10 miles) since break-in maybe 500 miles ago (maybe less - speedo not reliable) but didn't seem to run overly hot except in the hottest stop and go traffic. seemed to idle at normal op temp in the driveway for fairly long periods (15 min or longer. Upon trying to stop an exhaust leak, I pulled the threads out on one of the out board bolts. Not having a offset drill, I resigned to pulling the head and doing on the bench. It also gave me the opportunity to install the Holley intake, replacing the '67 273 cast iron one I was running. After getting it back together, and running a thermostat this time around, I notice it heating up right away. I pulled the thermostat and it caused it to heat up slower but heat up all the same. It didn't seem overly hot, but temps have been cool lately; 80s. I dove it to a show, Sunday about 15 miles away and it was alarmingly hot by the time I got there. Not as bad returning as it was raining then. I know I need another gauge but my Sunpro was reading 250*+. I say I need a new one because it never pegs down to 0 and you have to tap it as it sticks a little. (Stock doesn't work)

Can I assume the top end of the gauge reads fairly close? Or can I subtract the difference of about 140* that is the bottom end even tapping and its not really and issue. shruggy I have been chasing dizzy timing because timing light issues but have it just where it doesn't ping, but dead-stop hesitation is a problem I'm hoping is in the carb. Temp seems un affected by timing

Thoughts? Would the aluminum manifold be a factor (I thought it would be a + as less heat sink). There isn't a great deal of coolant noise when I shut it off after its hot (internal boiling or back-flow into the overflow.)

Thank,
Scott