Wrapped up the head gaskets this afternoon. Started it up and BOOM! a leak. Not a drip either, it's a nice stream running down the right rear of the engine. Ugghhh.

Any thoughts - please gawd don't say head gasket

 

either you did torque the head correctly or the intake gasket got pinched did you use black RTV on all 4 corners of the valley gasket?

 

You some where along the process, screwed up.
Did you follow a shop manual directions, did you have the heads milled, did you use ne head bolts and how did you torques the head bolts?

 

All the above plus potential fold over of gasket. Gasket too narrow on the coolant channel areas. Hope it is just an intake corner.

 

time to borrow or rent a cooling system preasure tester

 

Well, the good news is it's only on one side!

 

Advance auto has a nice pressure tester for rent.

 

Willing to bet it's the lower intake gasket

 

Same happened to me after HG replacement. Mandatory : Get a superb flashlight and check where the leak originates! It is not easy to spot under so much intake plenum.
I found the heater hose clamp by the front of engine to leak and the coolant has the habit to flow backwards by the right valve cover and down the rear right of block. Scary but easy fix; was not a head gasket issue.

 

I got lucky and did not have issues. But, I was SLOW at replacing stuff.

If you are leaking OIL from the back of the engine - it is probably that little gasket and metal piece that go on the lip of each end of the engine.

If you are leaking coolant -
Could be just a matter of the valley gasket.

Did you have trouble placing it in there? I did.
Did you put sealant on the valley gasket?
I did not and it turned out fine.

You may want to just torque the intake manifold again.
I know - a lot of work.