'79 Chevy 350 w/ Vortec Heads (1500 miles on the engine and heads)

I have coolant leaking from the pass side (front) of the engine but I cannot see where it is coming from. It only leaks when the car is driving. It won't leak when the car is idling - no matter how long I wait. Car never gets hot when driving.

I put UV Dye in the system and got a radiator pressure tester. It holds pressure fine on the gauge. Can't see or hear anything when pressurized. I'll lay under the car with it idling - with my UV Flashlight - nothing leaking.
As soon as I go for a little drive its pretty wet again in the same area.

Here is what I have replaced:

Water Pump (twice)
Lower Radiator Hose
Thermostat gasket
Radiator Cap (tested this too)
Lots of new Anti-Freeze

A few months ago I upgraded the Intake Man. gaskets to the latest Fel-Pro. Freeze plugs look ok. The Oil looks good.
I am at a serious loss as to where its coming from - any suggestions?

 

Have you tried revving the engine sitting still? Maybe it's causing a leak from the manifold or something under a load/different vacuum. Also, shouldn't the UV dye leave some sort of residue from where it's leaking? Even if the water evaporates or boils off due to the heat of the engine block/heads, I thought it should stick around to help identify the source...

 

Yes - I have tried revving it at idle to get it leak. After driving the UV dye is there - but its all over the place. I think the cooling fan spreads it out everywhere so yes, its hard to see the origin of the leak.

 

You can try to disable (unplug the power or ground wire) the fan for a short drive; just don't let it sit too long! That's if you think the fan is throwing your dye all over the place. It might help

 

is it leaking where the intake meets the cylinder head in the corner at the front of the engine....that's a very common place for a leak. Follow the leak up to the highest point....I'd bet money it's an intake leak.

 

I don't see any fluid (or dye) at that location. Also, I have about 20 miles on the newest design of the Intake Gaskets for Vortecs (they have some metal in them now). I checked my intake bolts and they are still torqued to 11 ft/lbs. I chose not to put any silicone around the water ports on the heads.

thanks

 

Not sure if you have a vacuum activated heater switch, but usually that is located right above the front of the passenger head. Checked that or any heater hose running above that?