[DeTomaso] Thermostat question

[steven.liebenow at att.net]

Somewhere in an old (perhaps 90's) Ford shop manual or so, I read something regarding the odd 192 degree value that was found on OEM t-stats, that claimed that this temperature was more optimum for better engine performance and minimizing cylinder wear.

At the lower temps, and startup, block wear will occur more than on an "operating temperature" engine.  The purpose of the thermostat is basically to regulate the temp of the motor to keep it in this optimum area, providing that everything else in the system is properly sized, you actually have air flow thru the radiator etc.....fans that turn....

When you start your cold car up, your cylinders are wearing because the coefficient of friction is more when cold. As the engine warms up, this value goes down....  The idea being that you want to keep the water in the block longer to warm up faster and once warm, regulate the flow out to the radiator.

In the winter, your t-stat comes into play by closing when the water coming back into the engine from the radiator is too cold! Normally we don't think about this with our sports cars, as they never get driven in the severe cold, but that is what they are supposed to do!  Again, regulating the temp.   For the most part, once our cars are warmed up, running in warm weather, the thermostat will stay open....and not do much at all. You are relying on the cooling of the radiator and the fans.....

I see two areas of operation on my temp guage.....I see the area that the t-stat opens and tends to keep the engine at for a bit, until I get into warmer ambient air, when then I reach the limits of the radiator and puny fans!  Two different plateaus so to speak.....when the air get's too hot, then the gauge takes off and you better get some air moving thru them tubes!!!

Someone was correct, in that the flow to the heater core is basically unrestricted, unless you have a variable valve in the mix. You do not want to shut this flow off 100% generally, as this can cause issues with trapping bubbles and cavitation.  All 70's+ Ford passenger car valves have a smallish 1/8" hole in the valve flapper to allow some flow, OR, in the metal heater tubes, there will be an "H" of sorts that always allows flow around the circuit.   There is nothing wrong with running a "loop" of hose from the outlet to the inlet of the pump.  Not having the loop is more of a risk in my mind, excepting pumps designed to not use that circuit altogether. 

The Mangusta was a horrible application of heating and cooling technology.  There was no provision for a thermostat, yet the heater valve configuration allowed for the "H" type configuration when the valves were shut off!!! You couldn't reach the heater valves from inside the cabin, so they were either off, or in "roast your ass-off" mode....as the smallest amount of hot water flow thru the heater core is enough to warm up that small cabin in a jiffy!!!

If you ever come across a block that has had a 160 degree or no thermostat in it for a long period of time, you will find that the cylinders will typically have more wear in them.  The outer "corner" cylinders in all motors will show more wear as they are the coolest.  The center bores will still have almost no wear due to the fact that they are sandwiched....and retain more heat.

In late model motors (Ford) that I have torn down and measured, I find that their bores are in amazingly good condition, with very little taper and ridge, even after almost 200K miles! Generally, the 5.0 guys can get away with honing the cylinders and slapping new rings and bearings in the blocks and away they go!!!  Not like the blocks of old.....  Keeping that operating temp up, and perhaps modern additives in oil has contributed to lesser wear!  ...then there's always the rumors of "more nickel" in the blocks..... who knows!

The least I will run in my cars in CA, is a 180-185 t-stat....after reading the info in the books and seeing what I've come across, and now understanding just what that little device does!!!

Ciao!
Steve