I'm trying to learn more about this car's cooling system components and what they do. I read the stuff in the service CDs but the information wasn't sufficient. I have attached four pictures to this post that show the items I'll be asking about.

From what I can see, the car has two sensors for the coolant temperature. Picture A shows what I now know is the sensor that tells the temperature gauge what to show right? That sensor is located right between the glow plugs, next to the injection pump.

Picture B however shows the second sensor, right after the thermostat housing (going from radiator to the engine). What is its purpose?

I can also see that the car has two cooling fans. Picture C shows what looks to me like a clutch driven fan located between the radiator and the engine. This is the fan that is supposed to exchange the heat in the engine coolant with the atmosphere via the radiator. Am I correct or not? In my engine, it seems like each time I look under the hood this fan is spinning.

Picture D however shows a second fan, located between the radiator (or condenser) and the grill. I can see an electrical connection, so it isn't clutch driven. On my car, I've only seen / heard this fan when I was doing a cooling system flush some months ago. It came on briefly as I was pouring water into the reservoir and draining it right away through the radiator drain plug and the engine block coolant drain plug, both of which were open. I since haven't even seen or heard it on. I know it works because I jump started it and it came on full blast. What is its purpose? To come on when the engine gets extra hot?

Thank you all for your help. Hopefully some ignorantos like me may also learn from my questions. :p

Attached Thumbnails

       

__________________
1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver