does swapping out rusty parts with newer parts actually change the performance of the car?

[Joshmc73]

i found a bus, it was in Ok shape, all rusty most of the parts were in horrible condition except the engine, all it needed was diesel and water. the bus kept powering off to what seems to be the coolant not doing its job. a few shut downs later, im at a garage kind of area, it has a coolant thats in better shape, i swap it out and fill the newer coolant up, and the bus hasnt shut down since.

[PrestonLK]

Rusty radiators lose fluid quicker and perform worse at cooling the engine. I don’t know if other rusty parts have an effect.

[Pete]

Rusty parts fall off easier in a crash, crusty tyres handle worse, and rusty radiators have terrible cooling performance.
A fully rusty radiator is just 12.5% of the cooling of a fully shiny one. Even the second grade of radiator, clean and silver but not gleaming, is only 75%.
The condition of the radiator is usually much more significant than its type. Always swap to a shinier radiator. A fully shiny radiator of any type is adequate for any vehicle and engine.
The best radiator is the fury radiator, you can tell which one that is because it takes 20 litres of coolant. It's an upgrade for the bus.
If you want to never have to top your radiator up again, find a fully shiny radiator, fill it with 10-20% alcohol, and the rest water. Don't worry too much about being low on coolant, 50% is the minimum amount of coolant to get 100% cooling.
Engines do not have rust or damage states, and cannot be cleaned or improved in any way. They are all the same.