According to a post over at forumdeluxx.de, Arctic Cooling's Accelero S1 rev.2 paired up with the Turbo Module fans can't cope with the heat produced by the HD 4870. According to the product page on the Arctic Cooling's Web site, this one supports ATI's Radeon HD 4850/4870 cards.

The problem, however, isn't with the card's GPU but rather with the VRM part of the card, which gets quite hot when cooled by the Accelero S1. It just seems the VRM part gets too hot without a heatsink and that's it. The situation got a bit better when the Turbo Module fans were replaced by a 120mm fan, but 98.4°C on the card's backside is still a lot. The product page on the Arctic Cooling site also shows that Accelero S1 comes with a special heatsink for the VRM, but it is unclear from the pictures if this user has used it or not.

Of course, Arctic Cooling has released a new Accelero Twin Turbo cooler that comes bundled with memory and voltage regulator heatsink and it packs much more cooling power with dual 80mm fans. Still, it's nice to know that you shouldn't try the Accelero S1 without making sure that you placed a heatsink on the VRM part.

You can find some pictures of the hotspots here.