radiator/water only?

It will run cooler but the problem with it is it will rust really fast.

You can run less of a percentage of coolant, say 70/30 but I would not run it without any.

yes the water has better heat dissapation than antifreeze but it doesnt have the rust and corrosion stopping abilities like antifreeze has. I would just run 50/50 mix, if ur overheating that bad then get some electric fans or bigger radiator. Im running h/c/i a 180tstat with Stock clutch and fan, stock radiator and shroud (my bigger radiator got a hole in it) and my temp doesnt go any higher than 190 in the summer maybe 195 tops in hot traffic.

Running water only isn't recommended, other than in emergency situations. The antifreeze raises the boiling point of the water, so you won't have to worry about overheating the water and having it boil over if you run some in your cooling system. Having the water under pressure in the cooling system alone will raise its boiling point, but I'm not sure how much, and I'd rather not take the chance personally. In addition to that, there's the point that 89sleeper mentioned about corrosion. If you'd like the engine to run cooler, pick up a lower temp thermostat, or get a different radiator with more rows, but keep in mind that your computer is designed to run the engine at a certain temperature for the most power and efficiency, so if you lower the temp too much, you'll also be hurting performance.

do not do only water!!!! there is a reason that manufacuters call for a 50/50 mix.... in the summer you can sometimes get away with 60/40 water/antifreeze.

As stated above, running just water is asking for rust problems. Still, if you're in a warmer climate zone you can get away with more than a 50/50 mix. Go 70/30 or whatnot and you'll be fine.

My thoughts-

What are you current coolant temps? I ask because it may not be beneficial to run cooler, it just depends on where you are now.
I have done some research on cooling systems, and this is what I have come up with. I know it is long, but it should answer your question quite well. Let me know if anyone has thoughts to add.

Unless you have some odd-ball combo the 160F stat will do more harm than good. The lower cylinder temps will increase bore wear, engine oil will not get up to temp, and power and economy will most likely suffer due to poor combustion. Depending on the source, ideal coolant temps will be anywhere from 195F to 220F.
Most people feel that the 180F stat is a good compromise. I ran one for several years in a stockish 302, with no noticeable problems.
Hope this helps by bringing up some of the factors to consider when changing the coolant T-stat.
The literatures I have read (mostly SAE published papers) tend to indicate that the engine is most efficient around 200F coolant temps. The coldest coolant temp I have seen for any test (whether analyzing power/emissions/economy) has been 190F, anything lower seems to be considered cold start. The highest temp I have seen in a test is 240F. At 350F the glycol coolant degrades to form corrosive acids. The 350F limit is a local temp, for example in the head, between the valves. I am unsure how to correlate the 350F max allowable temp to ECT sensor readings.
Coolant/water mixtures should be at 50/50 whether using ethylene glycol or propylene glycol. I have seen SAE published papers that tested different ratios between 30/70 and 70/30. The best all around performance tends to be at 50/50.
Water is a better cooling fluid than the glycols, but does not provide the corrosion protection.
Another danger with straight water, which is hardly ever mentioned, is Cavitation. Cavitation damage occurs when the coolant experiences brief low pressure, followed by a return to high pressure. This situation is primarily found in water pumps, but is also common on the coolant side of cylinder walls of diesel engines.
As the pressure drops, the coolant forms small vapor pockets. When the system pressure increases, the vapor pockets collapse. The collapse releases a large amount of energy, which can damage the surface of metal materials. Think of a bubble popping, but with much greater force. By raising the vaporization temp of the coolant, glycol additives will help prevent cavitation. Using a proper radiator cap pressure will do this as well, as increasing the pressure in the entire system will provide protection against local low pressure zones.

jason

if your motor is pretty new and clean than a 70/30 mix would be the limit

There are a lot of guys in hotter climates that run no antifreeze. They do run a wetting agent (or two bottles) and a rust inhibitor and lubricant package. But in Wisconsin is that necessary? I dont even try to do that and it gets to 115*F here. As others said, if there is an issue, address it instead.

And here is some info on heat transfer. Water transfers heat 2.6 times more efficiently than coolant. For every PSI of pressure in the system, that raises the boiling point ~3*F (so 16 PSI = boiling point raised from 212* on a system with just water, to ~260).
COolant does raise the boiling point, but it is a little catchy. Because it does not transfer heat as well, the system is not as efficient at dissipating heat. So the car might run a hair hotter with the antifreeze than with all water. But the slightly raised boiling point from the antifreeze makes up for it. I was surprised when I researched this stuff to find how little the antifreeze raises the boiling point, and how this raised point is mitigated. But you sure want that lubrication and rust inhibitation.

Good luck.