How bad is it?

I got a chance to get some server racks, but I don't have room to put them in the house. Only place I can put it is in the garage. Will the servers function properly in 80-100f abient temps in the garage? What are some bad things that might happen? TIA!

That is quite hot. It would probably reduce the life of the computer in general just due to heat. Another thing is the temperature changes could warp the boards enough so that the components pop off (especially BGA memory packages, northbridges, and such). The hard drives might also not like that hot of temperatures. Another concern is the humidity...if it gets changes temperature too fast you could have water condensing on the inside of the computer in fun places such as the PSU.

I had an oscilloscope die on me that way...I left it in the garage for a few months, came back home from college, brought it in, and it wouldn't boot up anymore. That wasn't a happy day