Most of the Z400s came with hotter running 130W processors, and as such most have the Performance rather than 95W Mainstream heatsinks/fans. There are thus a lot of those higher performance ones available for sale on eBay. In contrast most of the Z600s came with the 95W Max TDP processors and thus most have the 95W heatink/fan combo. The sockets are the same, but the Z600 inside design is a tight fit, and the Z400 Performance heatsink/fan will only fit on one of the two sockets of a Z600.
I'm assuming you are going from a single processor to a dual processor setup, and saw that the Z400 heatsinks were generally cheaper than the Z600 ones on eBay.
There is a little issue..... even that one that does fit is a tight fit, and you need to bend down by a bit the rear flat metal airflow deflector of that Z400 heatsink to have it fit in that one spot that it can. That is easy, works, and I have done that. The Z600 does not care if it has one 95W Z600 heatsink and one 130W Z400 heatsink. My recollection is that the Z400 heatsink fits only atop the second processor in a Z600.... the memory cooling shroud above the processors area makes it a very tight fit there in the Z600. Z600 130W Performance heatsink/fans do exist but they were so uncommon that they now are rare and expensive to find.
The vast majority of those Z400 heatsinks you'll see on eBay have a metal rear airflow deflector but there is a version with the same HP part number that has a black plastic airflow deflector instead. You don't want this one:
Image may be NSFW.
Clik here to view.
Note how there is also a top black plastic attachment of the fan holder to the top metal of the heatsink..... you can tell the two 130W ones apart easily that way. Just buy one with the metal deflector. You can't see the image until a moderator releases it (which I think is a waste of function in this forum where I never have seen an off-color picture uploaded).
If you have a "version 2" Z600 with the later boot block date then you have better processors to consider than the one you mention. I only install two of the fastest ones listed in the late Z600 QuickSpecs..... I got two of those for 70.00 a while ago by careful shopping:
X5672 SLBYK Quad Core 3.2GHz LGA 1366 Processor.... use that SLBYK sSpec code to search eBay.
If you are going to the trouble I'd recommend two of those assuming you have a version 2 Z600. They won't work on the version 1 Z600, which has the earlier boot block date.
