Temperature gauge fluctuations

[nakabrd]

I have a 1971 GTX 440 automatic. It's stock except for Edelbrock heads and intake. Here's the issue. When driving around town with ambient temp about 85 degrees, the temperature gauge climbs about 1/3 up. When I get on the freeway going about 65mph the gauge climbs to 1/2+, and it might continue to increase. Does anyone know what causes this? Thanks for any advice.

 

[Dennis H]

100 reasons. Recommend a laser temp gun to start and get actual numbers. How about extended idle? Shroud in place?

 

[moes]

at highway speeds you have a rad problem, it could be restricted core-tubes or separated fins. At 2500 -3000 rpm the water should be circulating pretty good to keep a engine cool.

 

[nakabrd]

Ya, the shroud is in place. Thanks for the replies.