Tranny pressure line PSI

I know that the engine cooling system is under about 15 psi to raise the temperature at which the coolant will boil. is the
"pressure" line of the transmission that goes up to the radiator under similar amounts of pressure? I just want to know so i can predict how much fluid i can expect to squirt out when i cut into the pressure line to install a gauge sensor.

The transmission cooler lines are more "residual pressure" than anyting else - it's just enough to keep the fluid moving through the cooler.

There won't be any pressure in the lines when the engine isn't running (and driving the pump,) but there will still be fluid in the line, so you'll get a drip - but not a "surge." The remaining pressure in the line will be bled off into the pan, since the other end of the cooler is an open fitting flowing into the pan anyhow - so pressure in the line won't be a problem.

In fact, the cooling system also won't have any pressure to it, once it's cooled off (the pressure in the system isn't from the pump, it's from steam pressure due to coolant boiling initially. The additional pressure serves to raise the boiling point of the coolant, which makes it somewhat more efficient at design temperature.)

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