ATF cooler question

[4ePikanini]

The Gen4.1 has two heat exchangers

One is an ATF-to-Air radiator type and then it has a line that goes through the bottom of the engine coolant radiator.

If you bypass the engine coolant radiator circuit, will the ATF not be cooler as it's not getting the heat from the engine coolant?

[geopaj]

The Gen4.1 has two heat exchangers

One is an ATF-to-Air radiator type and then it has a line that goes through the bottom of the engine coolant radiator.

If you bypass the engine coolant radiator circuit, will the ATF not be cooler as it's not getting the heat from the engine coolant?

Yes, until your ATF gets hotter than your coolant. Coolant should sit about 88-90c. ATF however, without trying is easy to get to over 100c.

I’ve bypassed the engine coolant radiator circuit and added a 2nd external cooler.

[Azzx]

It will, but you will get higer fuel consumption city driving because of low at temp .
This is why some of at use thermostat or share the cooling systems.

[old Jack]

It will, but you will get higer fuel consumption city driving because of low at temp .
This is why some of at use thermostat or share the cooling systems.

In cold climates it is common to have a thermostat in the ATF cooling system because the ATF temperature needs to be above 40C for the torque convertor to lock up. If the TC does not lock up then you will consume more fuel.

This is not a problem in Australia as if would rarely get below -5C for extended periods, so bypassing the ATF cooler that is integrated in the radiator is not a problem. However if the vehicle was operating in cold climates regularly I would advise to keep the integrated ATF cooler in the cooling system.

OJ.

[twisted32]

The effectiveness of the rad cooler changes dramatically with weather/driving conditions. I have been monitoring lower rad tank external temperatures for quite a while now with a surface mount sensor (would prefer actual lower tank coolant temp, but that is problematic in a plactic tank). I have seen indicated temps of around deg above ambient at highway speeds through to 80 degrees in hard low range work ie soft beach work (Southend to Vic border) or High country climbs in summer.
It is only in these extreme situations that as the first transmission oil heat exchanger, that the rad cooler would not be dumping some heat from the trans oil into the coolant.
The rad cooler, especially around town in stop start driving, has much more thermal capacity and is able to maintain a more stable trans oil temp.
The big negative for the rad cooler is, if it fails, and you get water/coolant in the transmission, it is rebuild/replacement time...