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Hello Gentlemen,
I have a coolant leak that I have tracked to somewhere above the rear valve cover. The leak gets lost somewhere behind the manifold. This is on a newly rebuilt 356 engine that has been warmed up about 5-6 times.
Can a head gasket leak externally? I have not re-torqued the head. Do any of the manifold bolts enter water in the block?
Thanks,
Mark

Yes to both questions. Retorque would be one of the first things to try. As to studs into the water jacket, the stud leaking was apparently enough of a problem Packard introduced the new rolled thread studs during 21st series production to help with the issue. I would think you could see water around the nuts if any of those studs was the source. You might be able to pin the area down with one of the fluorescent leak detecting kits.

Best practice, always use gasket shellac or Permatex on the threads of any fastener that enters the water jacket, and do your first torque of head studs within 30 minutes of first startup. 2nd torque after a few hours of running, and again after 500 - 1000 miles.

Thanks guys, this gives me something to work with.

Let's assume it is one of the rear manifold studs. Pretty sure I did not seal the threads when I hung the manifold. Can I seal them one by one without removing the manifold?

Have been thinking exactly what we had a problem with in manifold studs and water jacket. It was a long time ago so I may have to rescind my yes they do and say yes they can.

The more I think about it the problem we had was on one stud and caused by the machinist removing a broken stud and drilling in too far causing the leak. IIRC our issue was more in the center of the engine. The head studs and a couple of water pump bolts definitely go into the jacket but not that sure on the manifold now. I'd still re-torque and get some fluorescent dye before removing anything.

Happy to report that after a head re-torque, the block held 7 lbs of pressure with no leaks for 48hrs. I will follow the suggested tightening schedule. Thanks gents....
Mark

Glad to hear the problem is apparently solved and you got to it before your new headgasket was damaged. I'm curious, on the first re-torque how much did the headbolts turn to reach the torque spec? Just by memory I seem to recall they often took at least 1/8th of a turn, maybe a bit more.

I was surprised how much some of the bolts turned. Most were pretty tight, a few turned more than 1/8th. Some bolts are not easy to get at with a long torque wrench, so I ended up pulling the plugs for more room.

Also glad it was a simple fix. Maybe your machinist had one of those operation interruptis things and forgot where he left off when he came back to finish.

Mark, just keep in mind that the head gasket is compressible to a certain extent so the next retorque is equally important. Years back when the majority of engines were flathead, a check of the head bolt torque was considered a routine part of a comprehensive tune-up. And so it should still be today.