How do I know the block heater in my 2009 Honda Civic is working? Does it make anoise when connected to a power source?
I know of two block heaters which actually get the job done (there is a kind which attaches to the oil pan to heat the oil, but I do not see this working very well).
The first type is the kind which replaces a freeze plug in the engine block. I believe this is the main kind which you can get for Hondas from the manufacturer (at least I've seen them offered by Honda for their vehicles). These do not make an inherent noise when working. You should be able to feel them heat up right after you put power to them though. I don't think I'd keep a finger on them for too long, though, because I bet it would burn them for you.
The second type is the kind which goes inline in the heater coolant hose. Once this type is working for a while and the coolant starts getting warm, you'll hear it as coolant is being pushed by the heating action. There will be an intermittent boiling bubble sound coming from it (don't know how else to describe it).
In either case, there isn't any motor or anything which pushes the water around, so you'll hear no motor or pump making any kind of whirring noise. These heaters use convection to move the coolant around.
If you can follow the power cord back to the heater you should be able to determine what type heater you have. A true block heater will be installed in the block, usually in place of a freeze plug. You may also have a coolant heater which in typically mounted in a radiator hose. The hose is cut, the heater is clamped between the hose ends. You may also have an oil heater. Oil heaters come in several types. The simplest is a dipstick that contains a heating element that replaces the factory dipstick. It may also be attached directly to the oil pan either on the outside or internally. How long it needs to be plugged in to feel a temperature difference will depend on the size of the heater and the outside temperature. I would think an hour of being powered on will result in a noticeable difference that you can feel with your hand.