I have a 66 chevelle with a 350 .30 over what would be a safe operating temperature to run at thanks

Anywhere from 180° to 195° would be fine, as long as it stays steady at the TStat rating. If it creeps over the rating, it's not necessarily a problem but indicates something within your cooling system may not be as good as it could be, but won't necessarily hurt anything until you get a lot higher (220+ would start me worrying)

Is it normal for the temp to rise a few degrees after shut off i just installed a new heater core but it is slightly smaller than the original would that make much differance thanks

Is it normal for the temp to rise a few degrees after shut off i just installed a new heater core but it is slightly smaller than the original would that make much differance thanks

That's normal. The water is no longer flowing, temp gauges read water temp. The heat still in the heads and block will raise the water temp after shutting down the engine. That's when you usually see older cars with no overflow tank puking antifreeze on the ground.

Yup,thats heat soak which is common.

When you shut down a motor up to operating temp showing for ex 190 deg it can easily & quickly heatsoak/shoot up to 220-230 deg in a few mins post shutdown esp with temp sender in the head by exhaust port/ex manifold.(a big fat all stock 700LB+ of cast iron & steel heat soaked BBC motor is real good for doing this/LOL!!!) .

Temp sender being installed in the head vs intake can typically read 15-20 deg hotter then rest of motor is seeing at that same time due to to temp sender being installed by the known hot spot being the ex port/ex manifold.

Scott

Thanks for the input guys i will keep monitoring the temp as it is in the 180 195 range i have only fired her up a couple times since new heater core install