How do you do a flow test on a car radiator?

This is a method shown to me by a radiator

repairman years ago and has served me well. One can be easily

baffled by test instrument companies but this simply tried and true

method works for most cars (including full size passenger cars from

the old school category). Adequate coolant flow through this type

radiator core can be gauged very simply with the radiator in the

car. Drain the coolant from the radiator (cool engine) then

disconnect the bottom radiator hose from the radiator. Using clean

and suitable water flowing through a 3/4 inch hose at 80 psi

nominal/ 14-16 gallons per minute, insert the water hose into the

fill neck of the radiator. The water should flow freely out the

bottom of the radiator.

Radiators can be tested on a radiator test stand, these are

expensive machines so not many shops have them or working ones at

least. A find most shops that repair radiators just plug the bottom

end ( cross flow turn it on its side) and fill the radiator with

water and then unplug the bottom and watch the flow of water coming

out. You really need to know the flow rate of a new radiator for

your application as a base line. A big Detroit Diesel would be

about 110 GPM (Gallons Per Minute) vs a pickup at about 55 GPM.