3 Answers

Explain the purpose of your so called "heat collector" and you would probably get a more definitive answer. A radiator is a radiator i.e.; heat exchanger. They do what they are intended to do in a very simplistic manner. The thing of it is, there are different designs better suited for different needs and applications. So you really kind of need to establish the parameters of what you are doing and expecting from such an application.

If you are planning to make a solar water heater using the radiator, it should be suitable.You need to paint it black and enclose it in a box with a transparent front and insulation behind, facing south if you are in the northern hemisphere. Connect it to a hot water cylinder and you will get warm water and sometimes hot depending on your location.

Doubtful that it has the surface type and square surface area exposed to the sun to make it very effective.  Enclosing it like nomdeplume states would definately increase its heat collection capabilities.