When putting new coolant in the engine, some bottles say use distilled water, and others don't make specifications. It seems better to use distilled water because it would reduce mineral buildup, but I've never put anything but tap water in my cars. Can anyone tell me exactly what the benefit of using distilled water is?

Less things that cause scale and clog the passages. Limestone and calcium are bad for that.

------------------
350CID, Vortec 062 heads, Magnum 280, Performer Intake, Holley 650 DP, 3.42 rear w/ Auburn posi, 2600 Stall/TC
"Things are more like they are now than they ever were before."
Former U.S. President Dwight D. Eisenhower

I can tell you that it most likely won't make a bit of difference unless you live in an area with hard water. If you do, then use de-mineralized water. If you don't then I wouldn't worry about it. I have never had problems using tap water where the water wasn't slammed full of minerals.

Most boat engines run on whatever water the boat happens to be sitting in at the time. Fresh, salty, muddy, raw sewage, whatever. You should see the buildup inside an engine run in salt water for a few years. However, please note that it does take years to cause a problem, even running in some pretty foul water.

<font face="Arial,Verdana" size="2">Originally posted by Damon:
Most boat engines run on whatever water the boat happens to be sitting in at the time. Fresh, salty, muddy, raw sewage, whatever. You should see the buildup inside an engine run in salt water for a few years. However, please note that it does take years to cause a problem, even running in some pretty foul water.</font>

Yep. When I pulled the power head off my outboard (a 1981 Evinrude) it was full of junk.