My 1988 B150 leaks coolant ONLY after I shut off the engine. However, whats strange is, the coolant is dripping somewhere from the back of the block toward where the motor meets the tranny, and also, even when I drive it for 15 or 20 minutes and the motor is nice and hot, I shut it off and only then does it begin to leak but COLD coolant first and then it gets warmer and warmer coolant leaking. Weird! First off, how could there be ANY cold coolant anywhere in the system after driving for 20 minutes? Second, why does it only leak once the engine is shut off? Third, why does it start of with cold coolant getting warmer as the leak progresses. Like I said, its coming from somewhere in the back of the block and leaks about a cup worth of fluid before stopping.

 

It is from the blocks freeze plugs in side the bell housing of the transmission. The coldness is from the circulated air inside the bell housing as the flywheel and torque converter spin. The flywheel is cold and as the coolant drips on it the flywheel absorbs the heat, as the leak continues the coolant starts to retain the heat. The dripping may still be happening with the engine running and being spun inside the bell housing. You may find it splattering on the ground if you remove the bell housing inspection cover on the bottom of the bell housing.

 

Here's a picture of the rear of the block so you can see the two freeze plugs. They're the silver caps at the left and right sides of the block. The one top center isn't a freeze plug, it's the back of the cam, and those two screw in plugs next to it are oil galleys.