It will only leak under pressure, so you need to take a pressure tester and pressurize the cooling system and then look for the leak while under pressure, under pressure, under...well, you know how the song goes.
AutoZone rents them.

 

That is the only/most common coolant leak, so have someone pull it down, your searching for it isn't going to fix it, time to get dirty.
At the same time put on a set of Magnecore 8 mm plug wires, replace the t/stat and hoses if you are over 80,000 miles, make sure to only use Dexcool coolant.

 

I have a similar leak and am REALLY hoping it isn't a Head Gasket .. but here are the symptoms:

1997, V8 - just purchased.

Noticed that I wasn't getting much heat - checked the coolant level and indeed - I was down about a full jug's worth

Of course now that the system is pressurized at full volume, I am getting a good leak under the vehicle - none there before ... bone dry.

There isn't any obvious sources from the hoses I can see on the top of the engine, and the drips are coming from the engine/tranny mating surface - obviously a low spot. About a drip a second. There are some signs of fluid near the pipes around the power steering system.

So - it must be something further behind ... not sure what other than a HG. The weird thing is that it never did it until I filled the system up (I think it takes about 3 gallon full).

I am hoping it isn't a huge job to fix ... or am I FUBARed and will have to tackle a blown head gasket job?

Thanks!
Richard

 

Get a pressure tester (rent from parts store) and keep 15 psi on it, and find the leak. Easier done with engine not running. Rear of engine can be HG, valley pan gasket (easier than HG, but part of HG work) , freeze plugs (take engine or tranny out), or an odd hose you have not seen. Can't drive truck like this, running with low coolant = blown HG and/or excessive engine wear from over heat, including slipped sleeve, siezed engine, etc. All the while the temp gauge will show close to normal until whamo! Ultra Guage or scanner can help keep an eyeball on changing temps, then you decide when to react.

The valley pan gasket pic - the 4 corners are the coolant passages. Some bolts have been found finger tight.