A-body, Fresh 318, RV cam, Perf intake, Eddy 650cfm, headers.

Runs fine. 190* when cruising. If left to idle (800rpm) for 5- 10 min temp climbs 240+.

I have JY 26" radiator that I had re-cored, no shroud. Stock fan, orig belt set-up. Std 180* thermostat, I think.

Why does it overheat at idle? Do I need a shroud?
If so, I may need rad/shroud from aftermkt, where should I look?

Thanks.

Shroud. correct fan spacing. possibly faster fan speed(ch pulleys).aftermarket water pump(w disc).

Does it have a fan clutch? That could be a problem too......

In any instance, a shroud and proper fan spacing should always be used but I'm concerned it's something else considering that it's jumping that far to over 240 in just 10 minutes time. My car responded well once I got the right fan and shroud, but it only helped me to run from 205 to 190, and that was a sloooow climb to 205 before the shroud.......

May not be your problem, but - Check the fan - I have seen more than one installed backward so it was trying to push air rather than pull.

Also improper timing can cause too much heat.

Open/remove the radiator cap while the motor is still cool. Check for water flow once thermostat opens. No flow, could be a bad thermostat (or bad pump). Which direction is it flowing - should be toward the lower hose (wrong pump or reversed impellers are rare but possible).

Use an infrared temp gun on the radiator to check for cold spots (blocked radiator). This also verifies the overheating is not just a bad gauge sending unit.

Scott