318 manifolds heat unevenly

Oh yeah, I have the copper tubes. My manifolds are just a couple years old and I got the copper tubes with them from Barr Marine.

I didn't say anything about holes in the head blocked with gasket maker. Somebody else above was talking about switching the intake manifold with a car one, or using an automotive intake gasket. I've done neither.

But I have put the exhaust manifolds together from scratch, and I can't recall what kind of gasket I used at the ends. So I guess it's time to pull them and see what they look like.

Thomas

I should've provided this info earlier in the thread, but better late than never. I'm pulling the rear elbows off the exhausts tonight. Here's how the water currently routes through my engine.

The driver's side thru-hull pickup feeds the front impeller chamber. That continues to the front cover inlet. The front cover outlet goes to the intake manifold inlet. The water flows out of the intake manifold through the thermostat housing in two directions, (1) and (2):

1) The first is an overflow that appears to leave the thermostat housing before the thermostat. That hose connects to a t-fitting that runs to both exhaust manifold elbows at the inside rear of each manifold. That goes straight to exhaust.

2) The second hose leaving the thermostat housing returns to a t-fitting that is immediately after the driver's side thru-hull fitting. That returns water to the hose leading to the rear impeller chamber.

The passenger's side thru-hull fitting immediately splits into a t-fitting. See #2 above for one of those splits. The other side of that t-fitting flows to the rear impeller chamber. Water leaving that impeller chamber flows to the top of the trans cooler. Water exhausting from the bottom of the trans cooler splits in two directions: (A) and (B):

A) Water from one side of the trans cooler flows through a hose under the engine and enters the driver's side manifold at the bottom rear.

B) Water from the other side of the trans cooler flows to the passenger's side manifold at the bottom rear.

Both manifolds dump the water overboard through the exhaust pipes.

And now, for the exciting conclusion:

Saturday night I pulled the elbows and front end caps off of the manifolds. I did use properly blocked gaskets when I installed those parts, but apparently I just used "paper" or "cardboard" gaskets. Whatever the material is, it didn't stand up to the water & gas pressure. Sure enough, on the manifold on the hotter side, the gasket material at both holes on either had completely opened up. On the cooler side, one hole was beginning to open up. Both lower holes were still completely blocked. So off I went to NAPA to obtain some genuine exhaust manifold gasket material. This time I got the stuff with "cardboard" material sandwiching a sheet of metal inside. I cut it to fit, but for the rear I only cut out one hole large hole for the main exhaust, one hole at the top for the water to flow through, and four holes for the bolts. At the front I omitted the large hole for the exhaust. Once I got the new exhaust manifold gaskets installed, both manifolds now run 120-125º at the top front, and slightly cooler at the rear. Whew! Yes, these Chryslers are very particular about proper cooling.

What does PCM have to do with my installation? Mine's a Chrysler. Was PCM around 1969-1974?

I'd still like to hear from anybody who can tell me whether my boat is plumbed "correctly", since I don't think the above conforms to any published diagram I've seen. But I'm pretty sure this layout is the way my 1969 Barracuda was plumbed, and I've just duplicated it in the Southwind 18.

So, big heaping helping of gratitude to 89Martinique for steering me in the right direction.

Second time a Ford guy has blundered into this conversation. Sheesh! You guys sucking too much Mopar exhaust!

Thomas,
At times it sure takes lots of hunting to find the problem but I'm glad you found it was just a simple gasket issue.