something I noticed about the eclipse systems

Yea, It sounds like the water is used to keep to motor cool but in turn it will transfer heat. I guess it depends on the ambient temperature in the room.

:OT: Aren't White Cloud Minnows cold water fish? Can they adapt to a warmer climate?

Hmm, I have both an Eclipse Three, and an Eclipse Hex 5, and I haven't noticed either of the motors getting too warm. However, while I have C/A, both my tanks hover around 80-82 during the day time the summer months.

I would tend to think it's just the heat of summer, and not the motors (they shouldn't cause that big of an issue with the tank heating up).

I have an Eclipse 12g and I haven't notice the filter motor housing to be excessively warm. I'd say may be just slightly warm. The bottom portion of the motor housing is submerged and I guess there is likely some heat transfer, although it's difficult to judge how significant it is. I think the light probably contributes more heat than the filter. The light cover and the hood directly above the light on my tank get quite warm to the touch.

What kind of light do you have on the tank? Between the heat from the light, the ambient room temperature, and the heat from the filter housing, I suspect the first two probably contribute more heat.

If your only reason to replace the filter is because of the temperature, you may want to first try running the tank for a day without the light and check the tank temperature throughout the day to see if there is a noticeable difference (taking into account your ambient temperature). If you are able, you can also relocate the fish elsewhere for a day and run the tank with the filter off to see if it makes a difference in the temperature.

Hope this helps.

Edit: typo correction

Some of us keep our tanks cool by placing a fan near by, and allowing the cool air to blow over the tops of the aquariums.