Installing 4th HDD - heat issues?

I am going to upgrade my computer by adding in another harddrive. It's a HDD WESTERN DIGITAL 320 GB 7200RPM/ SATAII/ 16MB INTELLISEEK, and as I've been reading IntelliSeek is a way for the HDD to use less power and spin less(and thus also generate less heat) when seeking a certain block of data.

The thing is I already have 3 harddrives inside my computer. I don't have any software way of checking their temps but last time I had a thermometer placed on one of them it showed 50°C. As it is they are fairly spaced, with one hard drive slot distance from one another. If I buy another one I'm gonna have to slide it in inside one of the empty slots, which will leave very little space between the drives. For a more ..."graphical" description I have taken a pic of my computer. As you can see they're going to be pretty crammed in there. I'm worried about heat.

To the right of the empty slots(where it's too dark to see) there is an air vent with four screw holes. Most likely for adding a harddrive fan. As I have pointed out in the pic I have an extra fan on the case. Do you think it could get dangerously hot in there if I add the new drive? I also at the time didn't bother to check the size of the metal frame against the fan, can anyone tell me if a generic fan can fit in the hard drive fan place?

 

Draw air in? So you're saying I should mount it in such a way that it draws air through the drives instead of blowing air onto them?

Btw how's 50 degrees for a drive? For the past 2 years I have had them close together instead of spread like they are now.

 

Most people but an intake fan in the front lower part of the case. That helps cool the drives. Everest (assuming you are running Windows) will show the hard drive temps if the drives have a sensor on them. http://majorgeeks.com/download.php?det=4181

I have one 120mm fan as an intake fan and my drives are usually around 32C.

E