The only time I've seen something akin to a coolant leak was with our 75 Alfetta sedan, where there was a casting bubble in the head which broke open between a cooling passage in the head and one of the exhaust passages. We kept getting an excess of steam out the exhaust, and a slow loss of coolant. Kept thinging it was a bad head gasket, so changed it, but the problem didn't go away.
Decided to pressure test the coolant system with the exhaust manifold and intake off to check for a leak somewhere. Noticed coolant coming out of one exhaust port. Using a light and mirror, looked in the passage and saw what looked like a shiny wire crossing the passage. Turned out it was coolant squirting out of the broken open casting bubble. Had to have the flaw welded up. All fine after that.
So, yes, it could happen, but very very rare. I'm really not sure this is a coolant leak. Under pressure, the plug tunnel would likely fill pretty fast if there was any leak worth talking about. Enough to short the plug.
Is it the same cylinder which shorts the plug, or does moving the plug move the problem with it. If it does, it's the plug. If it doesn't, it's not. Same for moving the ignition coil. Does the plug problem move with the coil, or not? If it does, it's the coil. If it doesn't, it's the plug.
If the problem stays with the one cylinder regardless of what you do, then maybe, just maybe, there is a problem with the head.
Will tell a funny story: l had a friend with a 62 Ferrari GTE 2+2 which had a miss in the V-12 engine. Could not figure out what the heck the problem was. Changed plugs all around and same problem, and always the same cylinder. Come to find out, when the engine was revved above a certain rpm, it was noticed that one piston traveled up just a bare fraction a little higher in the cylinder, and just barely tapped the plug prong closed, shorting out the plug, the normal clearance between the plug prongs and the tops of the pistons being sooo close, that it was just enough in one cylinder to cause this problem. He solved it by using two plug washers on the one plug. Ran fine after that, lol.
89 Milano (wife's daily driver since 1989, Shankle Sport)
91 164S (my daily driver since 1994)
94 164LS (~Q) (trip Alfa since 2000)
72 Morgan 27 (water time since 1976)
previously owned since 1964:
62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
Last edited by Del; 03-07-2017 at 10:31 PM.