Alrighty, so pulling apart and cleaning my loop was a pain in itself (glad I only do it every 18-24 months), but the kicker is that shim on the 7970. The 7970 is actually designed well for the enthusiast who sticks with the reference cooler. For instance, with only taking out 6 screws, you can take off the shroud to get full access to the heatsink to clean the dust out of it:
Anyway, here's the dreaded shim:
It's huge and would be a PITA to remove. It looks to me like it's there to protect the exposed circuitry on the package. Why they designed the package this way I don't know, but it is what it is. Because of that shim, you can't get decent contact with a flat mounting heatsink. If you look closely at the picture, you can see little blobs where I tested TIM spread (using MX-4 now ), and it's just miserable. The reference heatsink has a little raised area around the core to make contact, so how does one remedy this? My line of thinking - I'm not waiting for a full cover block nor am I paying for one after I just got this MCW82. Therefore, I made my own shim:
This is simply copper plating. You can get it at any hardware store or super store (Home Depot, Lowe's, True Value, Ace Hardware, etc.) as it's used for decorating/plating/moldings, etc. It's ~1mm thick (forget the actually thickness), and I picked up a 12" x 6" plate of it years ago for ~$6. It's probably more expensive now since copper prices have gone through the roof, but it's a lot cheaper than a new heatsink . All I did was round the edges with 400 grit sand paper and then sand the entire piece with 1000 grit to remove oxidation. Here's what it does for the mount:
BAM! We're in business. Of course this totally screws the mounting for the MCW82, since there's no way that's what it's set up for (regarding total thickness of back plate -> water block, screw length, etc.). I toyed with a few ideas, I actually wanted to to a spring-loaded design to introduce some compliance in the system, but my local Ace Hardware (the only place that carried half of what I needed) didn't have springs small enough. Therefore, this is what I did:
Sorry for the poor quality, I'm actually using a flashlight to illuminate the block so the flash doesn't hide the detail. Basically, you can see the block making excellent contact with the shim. This is a direct screw on mount, a la water cooling from a decade ago. This is a very "dangerous" mounting mechanism as there's little forgiveness for over tightening (think cracked core). I probably pansied out and the mounting pressure isn't that great, but temps are actually fine. Again, I would have liked to use springs, but they weren't available. Basically I use the nylon washers to judge thread lengths and eyeballed the rest. These are 2/56 x 1/2 screws + metal washers on the top, for those of you interested. The final product:
Got everything installed. You can see the VRM's are cooled by cutting MOSFET heatsinks in half. You can also see there's still a lot of air to bleed out of the loop, but that will come (I run a closed loop, no reservoir, so it takes awhile to make it out the T-line). Still, it looks a heck of a lot better than the old loop, right?
See the next post for performance updates.