Jim, both you and 95h are using a lot more electricity than I care to.  And thanks for the temp testing to at least give a little credence to my thoughts.  At least you know now what your heater is doing and how fast it's heating your water.

All my waterers are using (recharging from) surface water supplies fed through underground lines.   It's colder water than you're using, but thankfully I'm also south of you too, so I don't feel too bad about the cattle drinking cold water. 

I don't think the perfect waterer has been invented yet -- cheap, effective, & reliable, what am I missing?

I've converted over to all energy free waterers.  The ones behind ponds all have overflow drains that use flowing water to keep them open, and there's no economically feasible way of bringing a steady supply of warm water to most of our fields as they are pretty fair distances from electric lines and I don't want to try and maintain LP burners at all of them (right now there's 9 of them).  The ones on rural water are using heat wells made from plastic barrels.  2 Cobetts, and 1 Ritchie Thrifty King. 

One of the waterers behind a small pond is one of the big construction tires, works pretty good, and by soaking up winter sun will basically clear itself of ice by miday even with no overflow water running -- unless there's been no cattle drinking out of it for several days and we have a brutally cold stretch of weather (0 and below = brutal for me but we do have it from time to time). 

The rest of the waterers are a split between Rubbermaid tanks and buried concrete freeze-proofs, all with overflow drains running.

One drawback to the black waterers we have here (cobetts, tire tank, rubbermaids) end up with what seems like scalding hot water in them in July & August for the first cow that comes to drink ... not so good when they really would be much better off with cooler water then.  But I also have seen them "spit/drool" lots of that hot water that time of year as well.  We generally don't mind allowing a small trickle of water to run through the overflows if the ponds aren't too low to allow it to try and offset this.

The Ritchie was originally installed by a Ritchie dealer and never did work right for the 10 years it was used.  As originally installed, it constantly froze up, a real PITA.   I started reworking the corral fences 2 years ago and moved/reinstalled the Ritchie in a way that it works much better now.  I put 2 - 30 gallon plastic barrels end to end vertically, below the frost line, under the waterer and used "isul tube" through the frost zone under the concrete to allow the warmer air to rise upward into the waterer from the "well".  I also  daylighted a drain out from the bottom of the heat well so that ground water wouldn't fill the "well" and eliminate the "air" (good thing a drain was there this year as we received right at 60" of precip for 2008).  The concrete pad also has 2" of pink styrofoam under it to help stop cold and frost from penetrating quite as deep.  Hopefully I can get a pic of this inserted here:

(fenceline Ritchie 005 small.jpg)

fenceline Ritchie 005 small.jpg (40KB - 1026 downloads)