[thisnametooktolong]

Originally Posted by shorod

I don't see where you're disagreeing with anything.

-Rod

That is because I was not clear and I did have a typo, Ford in all their wisdom (as well as GM and dodge) decided to trade temperature for fuel mileage. The hotter an engine runs the leaner you can run it until heat causes detonation. (Not all that leaner but better fuel anomiesation)
Mostly I was disagreeing with the idea that as long as it fluctuates in the normal range its A OK. The engine is expanding and contracting and therefore asking the head gasket to do a lot of work, especially on a bi-metal engines. The factory guage is a little slow and may not show the temp change for a while.
At the 2/3 mark that is around 225. The top of the normal range is around 255. That is way to hot. A 50/50 mix boils at 265. With an average temp of 235 I know for a fact that parts of the internal engine is over 265. At those temps I bet the inside of the engine looks just like a pan of water on the stove just before it starts a violent boil.( Little bubbles rising and a funny noise). There is no BTU buffer for what ifs and may-bees. The typo was that I stated the factory stat is not fully open till 115 it should have said 225. And my though on the subject of fluctuating temperature that I left out is: That is not good for anything. It is not good for the engine to run hot as heck because the oil does thin out. It is not good for the head gaskets to fluctuate with all that expansion and contraction going on. On an older engine that is running close to max bearing clearance on the rods. The round end expands making the bearing clearance out of spec. That combined with oil that is hot and therefore thin can and will cause problems. Ever notice that bearings spin more in the summer than they do in the winter? All of the engineers have the cars running on the razors edge as far as heat goes. That is fine and dandy when it is new, but not a good idea with a bunch of miles on them. A hot engine can and will go into thermal runaway because glycol dos not like to dissipate heat as well as it takes it on. This is amplified in an older engine that is not shinny new on the inside and a radiator that is a little dirty on the in and outside.
That is why when I purchased my sable I took the darn thing and rewired the CCM so that fans are always on low, turn on high whenever the A/C turns on. And turn on high as the factory computer says at 216. Then I placed a 180 t stat in it. Now the temp stays between 184 and never above 195, and the head gaskets are holding with 202K miles. But it does kill the alternator (life time guarantee… no problem)
As a side bar, if the fans do work on low and not high, the way the commands go to the fans, it is better to turn on the AC with the temp set to hot, and yank the wire to the A/C clutch, than it is to just turn the heat on. With the temp set to high and the core has water flowing through it and the fans are turned on.

And yep I know what happens to the heat in the winter, and what happens to internal engine ware below 180F.

Remember that I am not an engineer and this is just my thought on the subject, but it does seem to work.