What are the main signs that my car radiator is malfunctioning?

Leaks. Higher temps.

Welcome to Fluther.

If your engine is overheating, as determined by functioning gauges or by the red “idiot light” on your car’s dashboard, then your cooling system is malfunctioning.

It’s not always easy to narrow that down to “the radiator” unless it’s leaking, plugged, or blowing steam from the cap.

The temperature dial goes up unusually fast, AND goes up well beyond the half mark. Alternatively – if you lose almost all of the coolant – you will see steam coming from under your hood – if the coolant starts to boil you can damage your engine.

There can be 2 reasons for that: 1) cracked radiator and/or pipes, in which case you will lose lots of coolant fast, so like @digitalimpression said, check for wet spots under your car after leaving it parked for a while. 2) loose radiator cork. Either way if you suspect sth’s wrong, check the coolant levels and add some (just be careful, when the engine is still warm the coolant/steam can burn you if you open the container too fast) till it reaches about half and drive to a repair shop asap.

You may find explanation of radiators interesting. It is short and to the point.

Your engine is over-heating…. that’s the easy one.

Also worth checking the radiator fan, a lot of the symptoms are the same (save for leaks).

@tedd right, sometimes it’s not the radiator itself but a malfunctioning sensor linked to the fan.

There is a difference between your cooling system, and the radiator, which is just a part of it.
If the radiator is malfunctioning, it is either leaking or clogged. It’s pretty easy to see if water is leaking from the radiator. If the engine is heating up, and the water in the radiator is remaining cool, then the radiator might be clogged.