1.) The fan sticker is different.

2.) The patent numbers have changed

3.) The fan shroud has different markings: The extrusions are exactly the same for each Thermoengine. The only differences we could spot were between the patent numbers, and the text on the fan shroud. The original (hollow) Thermoengine has the following bits which appear to be absent from the current retail versions: "Thermosonic Technology Inc," and "sink & clip patent pend. world wide."

4.) The box is slightly different

Conclusions:

The focus of this article is only to illustrate the performance characteristics between the two versions of Thermoengine heatsink on the market. Looking at our test results, the differences appear to be no more than ~2-3 degrees, with a large portion due to a poorer performing fan. While we cannot speculate what factors brought about the design change, the alteration has not greatly affected the ability of this heatsink design to cool.

Where 2-3 degrees are significant to the stability of your computer system, the effect may indeed be significant, but for the most part it is a lot less than what we had anticipated. With the uniqueness of the hollow cylinder in mind we had expected to see a temperature difference between the hollow and solid Thermoengine of between 5 and 10 degrees, a result which would have been a significant departure from many of the tested samples. While the hollow Thermoengine is obviously more desirable, the solid version still offers fairly good performance characteristics.