What is normal operating coolant temperature?

[civdiv99]

I'd link to it in a nano-second if I thought I could find it again easily.

The currently installed mechanical thermostat supposed to keep 225 as a norm. The computer can override this by tossing 12v at the "heater" incorporated with/adjacent to the mechanical thermostat, thus artificially making that 225 thermostat open earlier due to that local heating. Under light throttle cruise it's supposed to run at at least 225. The most mine has hit is 110C on the OBC, but is usually right at 108C. Under whatever load conditions are predetermined in the system, the computer will activate the control and on mine has brought it down to about 104C. I dunno if it'll go lower or not - ran out of hill by then. However, I intend to run mine at 195, and there's a shitload of theory and practice out there about the effects of combustion chamber temperature with a gasoline fueled mixture. Too cool, and you risk gas falling out of suspension and cylinder wall washing. Bad juju on the street. Too hot and you raise the octane requirements - AND negatively impact how aggressive the timing can be (power to the people!).

The immediate predecessor to this engine ran at a more ideal 195 or so (for gasoline internal combustion efficiency vs. power; mileage = who cares, it's a V8 for a reason). In one of the E39 groups, there is/was a post describing (pics and all) retrofitting the 195 degree (ish) mechanical thermostat from this engine's predecessor (M60 or early M62 perhaps). The mod retained the electronic control, but that was for convenience and lack of fault code tossing since it never had to come into play. NOTE - this is NOT a "bolt-in," but was certainly not an engineering challenge either. Came down to a small aluminum spacer to provide clearance for the size difference in thermostats. The dude was quite happy.

The other approach is to monitor the engine temp yourself (2 pairs of wires on the "dual-temp" sensor, pick one set to monitor) and have your circuit control the active opening yourself. Probably somewhat less effective and possibly a bit harsh on the heating element, but much less invasive. And you have to have some hysteresis incorporated into your control circuit (thus isn't just switching on and off continuously over 1 or 2 degrees), and/or modulate the power delivered to the heater - with a PWM circuit, for example. This is probably going to be my approach - I already have the circuit scratched out, but if I'm not happy with the effectiveness, and the heater element cannot maintain what I desire (And I'm guessing it won't be able to once the thermostat begins to open and a fresh supply of water is allowed to flow past the heater element), then I will go with the approach above. Whether or not I use the actual BMW mechanical thermostat that was in this engine's predecessor or not is something I'll decide at the time.

Oh, and then there's the "who gives a crap, lemme see what happens here" approach. For $35 at Jegs you can buy a 12v thermostatic cooling fan controller. Instead of hooking that up to a fan, you just hook that relay to the heating element, and connect the original heater wires to a load resistor of correct resistance and load capacity to prevent a code, and see whatcha get. That's not what I would do, but I'm just sayin'.........