HOW TO MEASURE YOUR RADIATOR
By and large, there are two radiator designs: DOWNFLOW radiators and CROSSFLOW radiators.
As the name indicates, the DOWNFLOW radiator is distinguished by the direction the engine coolant flows in the radiator - from the top tank on the radiator to the bottom tank on the radiator.
The CROSSFLOW radiator is one where the coolant travels horizontally from one tank to the other.
No particular one of these designs is better than the other. Rather, they were made this way because of the functional design of the car.
It is very important for you to determine which type of radiator you have for measuring purposes.
CORE HEIGHT: As you can see from the diagrams, the core height on a downflow radiator is measured from top to bottom; the "height" on a crossflow radiator is measured from side to side. An easy way to remember this is that CORE HEIGHT IS ALWAYS MEASURED BETWEEN THE TANKS, no matter how the radiator sits in the car. Core height is represented by measurement (A) in the diagrams.
CORE WIDTH: This is the distance between the core side rails. DO NOT count the side rails in the width measurement of a core. The width is represented by (B) in the diagram for both CROSSFLOW and DOWNFLOW radiators.
CORE DEPTH: The easiest and most precise way to measure the core depth (or thickness) is to insert a small piece of wire between the fins on your radiator until the end is flush with the other side. Mark the wire and measure it for your core depth measurement.