“It just needs a radiator” – said the seller
The radiator is a mysterious component. There is no clear way to inspect if it’s clogged. The popular saying that “it just needs a radiator” is often the start of an expensive process of trial and error.
Maintaining a steady engine temperature is a balance of heat produced by combustion versus heat dissipated. When the system fails to dissipate heat, the immediate assumption is that the radiator has lost its ability to transfer heat. But this is half of the battle, it’s worthwhile to further investigate.
The biggest component to heat transfer is surface area. The radiator takes the flow from the radiator hose and expands it into smaller channels. This creates a pressure drop and slows down flow. The channels are surrounded by fins that draw heat away. Then as air rushes past the fins, the heat is transferred to the air.
How much sludge to block flow?
The heat conductivity of the radiator is important to some extent. Nearly all radiators are made out of aluminum and have excellent thermal properties. From that stand point, a coat of paint won’t be too detrimental to its function. However, a layer of mud or a bird nest are most likely going to get in the way of air flow.
The same concept applies to the inside passages. A small amount of water deposit is likely not harmful. If the coolant is clean and liquid, the radiator can be expected to be in good shape. But on engines that had a head gasket failure where oil contaminated the coolant, the resulting sludge will most likely be an issue.
In either case, it is a good idea to flush the coolant at the recommended service interval. Also, I recommend flushing a detergents through the system. It will dissolve build ups, clean out sludge and remove the suspicion of a clogged radiator. Beyond a simple fluid service, the radiator doesn’t require too much maintenance. It is a passive component.
The engineers took into consideration the amount of heat produced under extreme conditions. They picked a radiator large enough to handle those conditions. So it requires considerable effort to exceed the performance of the radiator. To improve heat dissipation, use an adjustable radiator fan controller to turn on the fan at a lower temperature.