I have a 496ho with a whipple and my temp reads about 145 while running on plane, but when I go done to an idle it goes up to about 160 or 165 is this normal, I just had a new sea pump installed so I know it is not that, what could this be.

I would think its just ALOT less water flowing a idle/low rpms .....should be ok ...my 2 cents ...

If it doesn't go any higher I wouldn't worry about it. After idling for a few minutes does it come down any? Don't forget , you still have heat built up from running

Mopower,
Thats what I was thinking, heatsoak. Maybe it would help to drill the T-stat as well. With my crossover set up I would see spike when coming off plane because it was actually running cooler then the T-stat would close due to being cool then spike just before opening.

Tim T.

BadDog,
My oil pressure does the same thing. 70 lb running , then 30/40 at idle. Lets it idle for 5 minutes and its back to 60 lb . Take off and 70 lb again.
A couple of 1/8 inch holes may help but may also lower your running temp too