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Coolant temp at idle


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Seen a few posts about the cooling system recently so wanted to share some concrete data from my car to help as reference.  My car has the 318i aluminum radiator, 80C thermostat, and I think a 13" Spal pusher fan mounted on the front, controlled by Megasquirt.  Here is snapshot from a datalog I took after a half hour drive the other day idling in my driveway:

Idle_temps.PNG

Upper graph shows idle, ~940 RPM (white), 12.4 AFR (yellow), and just under 40kPa MAP (red).  Now the cooling information is in the lower graph: yellow is coolant temp, green indicates the fan status (on/off), and red manifold absolute temperature (MAT, or the intake air temperature.  It was probably right around 90F ambient, and while driving MAT was probably around 95F.  But at idle, you can see how it starts creeping up as the engine compartment heat soaks.  Since my intake pulls from the nose, this is also a pretty good indicator of the air temperature that's being used to cool the radiator!  With my 80C thermostat, the car usually runs around 180F (~4 o'clock needle position) while driving.  I have the fan set to kick on at 190; you can see the vertical green line on the left where it comes on.  Even after it turns on, the temperature at the coolant divider neck still climbs a few degrees to ~193 by the time the cooled coolant makes it around to that point, and then the fan shuts off again (runtime ~30s) after it's cooled back down to <190 at the second green line.  190 corresponds to right at horizontal/3 o'clock for the needle on my coolant gauge. At the very right side (under the MAT reading), you can see where it bottoms out at around 187-188 before starting to rise again, another ~15s and we'd be back to 190 and the fan would kick on again.  But note too how the MAT continues to climb the whole time, up to almost 100F.  It'll level off eventually too, but with some recirculation around the radiator and not much other cooling happening through the closed engine bay, I expect it would take several minutes before going asymptotic.

 

So there you go, hopefully this helps show what's 'happening' in the 2002 cooling system and gives some baseline numbers for reference!

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