Radiator fin rust

[eagle]

Originally Posted by Benson

It is possible that the rust on the fins is from a small leak in the core that is letting rusty water from inside the radiator / engine block because antifreeze is NOT being used.

Even though the radiator is new they CAN have leaks due to defects or leaks from radiator cap.

Water in a radiator is the first to freeze long before the water in the engine block freezes.

Even though the radiator is new they CAN have leaks due to water freezing in the radiator core if antifreeze in not being used.

If the coolant is rusty, that is a problem. Clean it out well and put in antifreeze or another rust preventing coolant. You DON'T need rust on the inside any more than on the outside.