OK, finally got back home and was able to dig into this situation further….
First, I examined a 62 QD exhaust housing. I clamped the housing into a vise vertically, then jammed a fuel hose onto the bottom of the copper water tube. With the long fuel line above the top of the exhaust hsg, I slowly filled the hose with water until the water was just about level with the top of the exhaust hsg cooling intake passage. I did not see any water leaking out of what we guessed might be an intake water bleed off to help cool the exhaust hsg. So, that theory does not appear to be the case.
Next, I found a 1958 Sportwin powerhead, and had a closer look at it. I looked closely at the casting area around where the cooling water enters the powerhead, but saw no evidence of a cooling water bleed off. Next, I had a look at the rear of the powerhead where water exits into the exhaust hsg. I DID find a horizontal cooling water bleed off that is directed into the exhaust hsg, I’m thinking the hole is between 1/32-1/16" in diameter. Like I say, the hole is horizontal, although I’m thinking it is probably angled down just a bit to help cool the exhaust hsg. The exhaust chamber is open into the forward area as well, so I’m guessing this bleed helps keep the forward area cool as well. It should be noted that I found this same bleed hole on an FD powerhead as well…
I will work on posting some pictures tonight…Don
