# Replacing a Radiator

A typical scenario might go like this: An engine on a tractor, combine, self-propelled sprayer, or truck needs a new radiator and is beginning to run hot. You shop around and find a wide discrepancy in price, so you decide on the least expensive replacement.

You’re surprised when the replacement bolts right in; the holes, connections, and fittings are right where they should be.

Satisfaction with saving money feels great. That is, until you work the engine and it runs just as hot or even slightly hotter than with the old radiator. How can this be? Surely, it can’t be the radiator.

The job of liquid is to cool the engine, and it is the radiator’s task to cool the liquid. To do this properly, the radiator must be designed to meet the Btu rejection of the engine. Just because it fits in place has nothing to do with how it performs. Performance, instead, is most influenced by a radiator’s core.

Heat at the core
Heated coolant is circulated through the core. There, small quantities of coolant travel through the tubes that have fins attached to them. This is where the heat transfer from the liquid to the air occurs. The design of the tubes and fins is paramount.

Specifications such as fin density per square inch, the size and shape of the tubes and fins, whether or not a device is added to induce turbulent flow in the tube (very desirable), along with the material used to attach the fins and whether they go to the end of the core and butt up against the tank, all add up to making the radiator efficient. Some of these things you can see; many you cannot.

Do the math
A simple equation to calculate the heat rejection required by a radiator is as follows: Btu rejection per minute = 0.65 × engine hp. × 42.2.

For example, a 350-hp. engine would require a radiator that has the ability to dissipate approximately 9,600 Btu per minute to keep the engine cool under a load.

As a general rule, it’s best to buy a factory radiator replacement. It will have the exact heat rejection requirement for that engine. True, a factory replacement may cost more, but it will work as designed.

There are excellent aftermarket brands that produce the same heat rejection as the factory unit.