So, er, does anyone know the diameter of the thermostat used in the 3800?
Ran across one in the spare parts pile while cleaning up the garage today. It'* got an old Stant PN that'* no longer in their catalog, but the flange is marked 44mm. I think I picked it up years ago for a 60degree V6 motor.
As to the why run a 180 thermostat, pretty simple, more power at the expense of higher emmissions. And yes, on a street and strip car, I've run 180'*, even with a TPI V8.
Reasoning goes like this:
The original 195 thermostat keeps coolant in the block to bring the block and head temps up quicker, so the system can run a leaner mixture and burn very clean. (not great for producing power, but good for clean burn and hot cats) With a 195, I recall the head temps being in the 220 to 230 range. EGR starts working to help knock the head temps back down when they get too hot.
With a 180 stat, head temps are more like 210 to 215, mixture is richer, emissions go up a bit. EGR never comes into play, head temps never get high enough to cause it to recycle and cool the heads. ECM thinks it'* driving around on a cool spring day.
Flies in the ointment:
First, this only works if the radiator has sufficient cooling capacity to transfer the heat, either through the use of fans, or through the total surface area it can use. If your cooling system is marginal to start with, then the thermostat can't do anything about regulating the engine temps. (Which is why you should change the fan switch to a lower temp on, or program the ECM to kick the fans on at a lower temp when using a lower temp thermostat.) If the system can dissapate the heat without fans, then you can drive around all day with lower average engine temps just using a lower thermostat alone. (Which sounds like what some of you are doing already.)
Second, running too cold a thermostat on a ECM car can cause a big problem. You can actually cause it to stay in open loop indefinately (i.e. it never comes up to temp high enough for the ECM to start playing with the mixture and leaning it out.) This is actually a plus on a drag car...you want the thing to run in open loop all night long. On a street car it sucks when you pull up to the gas pumps.
Third, Running without a thermostat or some kind restriction in the block'* outlet can cause SOME motors to overheat. Small block Chevy V8'*, particularly the 400 motor, are notorious for this. How? Poor coolant flow through the block and heads. Without something in the water neck to restrict the flow out, the coolant doesn't get circulated through the entire block the way it was designed. The heads get really hot, yet the coolant temp looks fine till the whole system falls flat on it'* face. What is happening is the coolant around the combustion chambers is flashing into steam. Starts at the rear-most cylinders and slowly works it'* way towards the cylinders closest to the water pump. Put a restriction back in the water neck and the flow through the heads and around the cylinders improves, temps start behaving like they should.
(Added: BTW, the third scenario is pretty much why Bob is correct, in certain cases. While the SBC V8 isn't really on-topic, I use it as a worst case example of what is not really a design "defect", more like a weakness of the small block. GM knows it too. Look at the back side of an LT1 motor and what do you see..Extra coolant pipes leading directly to the rear of the cylinder heads...just to improve the coolant flow to the cylinders the furthest away from the pump...hmm, took 40 years for them to figure it out
Hope that helps the discussion a bit.