If you aren't having the fans turn on, i'd recommend not changing out your thermostat- at least until after you get the issue with the fans straightened out. The thermostat will not help matters here, as your cooling system is not functioning properly as it is. All the thermostat does is regulate the trmperature the coolant gets to before allowing it to flow into the radiator. So, if your radiator isn't cooling the coolant down enough/quick enough, this is the problem- in this case it'* being caused by a lack of airflow over the radiator'* fins- from the fans not turning on.
If you were overheating all the time- and your fans were working as they should, it would be a different story. But, in your case, by changing out your thermostat, all you will be doing is throwing another variable into the mixture, not correcting the issue at all.
Try checking/swapping your relay, testing for voltage to the relay, and check all the fan connections.
Worst case scenerio, you can termporarily wire in a switch to give you control over the fans- but even this isn't a true (or long-term) cure for the issue, and should only be used while you are chasing the source of the problem.
EDIT: Showshocka, I read your other post about the intake manifold issue. I have a feeling that given the situatiuon that you are already in there, dropping in a 180 would not be a bad idea- but don't expect it to be a cure for the fans not kicking on, or running hot while idling(no air cooling the radiator)
Hope this helps