At what temperate do the fans kick in on a KJ2?

And how does this correlate to transmission temperature, if at all?

I have recently installed an ATF cooler and noticed on highway trips the cooler is warm to the touch (seems about 40C to the touch) whereas after traffic driving the cooler is cool but the hoses are hot to the touch.

Is there a way I can set up the fans to go on when the ATF temperature goes beyond a certain point as they seem to be doing a great job of drawing air past the cooler?

At what temperate do the fans kick in on a KJ2?
The ECU has threshold settings for the main cooling fan that vary with vehicle speed and A/C activity, although only 2 pairs of threshold values are actually used:
1) 96C - On / 91C - Off
and
2) 105C - On / 100C - Off.

The first threshold pair only applies with A/C Off up to about 80kmh; above that or if the A/C is On the second threshold pair applies.

I'm not sure how the A/C fan is controlled yet.


And how does this correlate to transmission temperature, if at all?

I have recently installed an ATF cooler and noticed on highway trips the cooler is warm to the touch (seems about 40C to the touch) whereas after traffic driving the cooler is cool but the hoses are hot to the touch.
It only relates to transmission temperature to the extent that the ATF cooler in the radiator is influencing the coolant temperature.


Is there a way I can set up the fans to go on when the ATF temperature goes beyond a certain point as they seem to be doing a great job of drawing air past the cooler?
You would have to do this with extra relay control, as the ECU doesn't support this type of control. I would be finding a way to log the actual ATF temperature (*) first to make sure that it is not being kept within Mitsubishi's specs before going to the trouble though, as I've been informed that the nominal fluid temperature is hot by some standards.

(*): the auto trans code does support logging through MUT systems, but Evoscan won't connect to the TCU function :( I've found a way of logging the ATF temp via the ECU function but it requires reflashing the ECU and isn't suitable for casual use.

WytWun, are you saying the fans kick in earlier with A/C off than on? This seems somewhat anti intuitive.

As for correlation in temperatures I more so meant that maybe the same driving conditions that heat up the coolant most will heat up the the ATF most as well?

WytWun, are you saying the fans kick in earlier with A/C off than on? This seems somewhat anti intuitive.

Nothing is ever really simple, at least with ECUs... the code actually supports 3 fan "speed" settings. The main cooling fan in 3rd gens is only a 2 speed unit and in the A/C Off case the lower set of temperature switching thresholds (91°C/96°C) only applies to the "low" fan speed setting while the "medium" and "high" fan speed settings use the higher set of thresholds (100°C/105°C). In the A/C On case, the "low" fan speed setting is set to -40°C (i.e. always on), which I didn't mention in my previous reply - taking that into account, the behaviour is what it should be.

The inference I've drawn from the temperature threshold tables is that the "low" and "medium" fan speed settings apply to the "low" and "high" cooling fan speeds, while the "high" fan speed setting in the ECU is not actually used.

These cooling fan control tables are included in the published ECU definition files if you want to look at them in ECUFlash.


As for correlation in temperatures I more so meant that maybe the same driving conditions that heat up the coolant most will heat up the the ATF most as well?
I would expect that to be true in general, however the ATF heating could be expected to be less whenever the torque converter is locked (which would usually be at freeway/highway speeds).