Aluminum heads leaking coolant!

Are you using a lift when re-installing the heads? Even with them being aluminum a lift helps to ensure the gasket is not getting distorted when mating them to the block.

 

Oh Darn thought this was going to be easy LOL. So to understand the problem, no water in the engine, right? Just leaks on the outside? Both sides? Do you run a pressurized system? Water or coolant? Was your pressure-tester heated? Is there a performance loss after the leak starts? I have used the MLS gaskets and they are good enough for half a dozen reuses on serious race engines (max Compression). Not a real big fan of copper and coppercoat as it is extremely hard to be consistent. Any of the gasket design engineers will tell you that. The fact that there are so many approaches to the gasket dilemma shows how hard the problem is to solve (amongst the various manufacturers, race and OEM). I would still look very closely at the manifold fit and clearance. Different thicknesses of intake gaskets are available. The other thing is intake torque sequence. I remember a manufacturer (FelPro I think) put pressure transducers between the head and the block and then noted the values changing when the intake was installed. I think they did it with 302 strokers in mind and then offered a kit to put the big head bolts in. Hard to believe that is your problem, though. Did you try the calcium carbonate? (Iron Tite is the brand I use) This works for low pressure (cooling system versus cylinder pressure). Definitely check for exhaust in the leak. This a chemical and should be readily available. That will verify if it is cylinder pressure causing it.

 

Dowel holes deep enough?