I just pulled into the driveway and turned the truck off to hear a sudden hissing that was a very clear spraying coolant leak from somewhere in the middle of the back of the motor. I couldn’t get a clear look at it spraying as it was hot, but anything in particular, hose or fitting, I should focus on that may have cracked? Thanks!

Forgot to mention this is a 3.0 in a ‘95

 

something related to coolant bypass tube

 

i had a 22re with a crack in the water jacket, up and behind where the fuel filter is mounted, it was difficult to troubleshoot.

 

Best to mention the year, type of engine, etc in your post

 

Bolted to the back of the head is this gadget:

The large tube is part of the heater system. Here's the manual section that describes it: https://web.archive.org/web/20141114...06operatio.pdf

There's a gasket below the gadget where it bolts to the head, and all of the sensors could leak, but I'm guessing you just split the heater hose.

So all you need to do is get it up to temperature and look for the leak, eh? No, you'll scald yourself for sure. Take the easy way out and pick up a cheap coolant pressure tester like this: Then you can pressurize the system cold and finding the leak will be easy.