Manifold Cooling Passages Completely Blocked

[Xestenz]

Love the forum! Invaluable resource for those still committed to the Atomic-4.

Have a strong running late model raw water cooled A4 in my 1973 Tartan 30. Boat is on the hard, and have been performing some upgrades and maintenance to the motor (water jacked side plate stud upgrade, thermostat housing replacement, block water jacket cleanout and backflush, etc.). After buttoning up the engine and trying to start, noticed that no water was being drawn into the engine at the source (a large bucket). Traced the issue to the exhaust manifold (water flows freely and cleanly through the block to the thermostat housing), and it looks like the exhaust manifold cooling passages are totally blocked.

Have tried to backflush and forward flush with fresh water under pressure plumbed with a garden hose to the intake and outflow fittings on the manifold - no water will move through them.

Couldn't get the manifold hose elbow fittings off on first pass, and rooting around with a wire hanger through them didn't do much due to the hard angles, etc.

Engine was acid-flushed a year before being put on the hard, ran at proper temp, and saw light use during that time. Boat has been on the hard for a year in Seattle while performing some upgrades. Probably could have done more winterizing by draining all water from the block and manifold or running antifreeze through the system. Did leave hoses disconnected throughout the winter, and there are no external signs of freeze damage, cracking, etc.

Any ideas on how to proceed getting the passages unstuck if pressure water won't do it? Have never pulled the freeze plugs before, and not sure what that would buy me. Are the internal passage shapes complex enough to preclude effective 'rooting' out in place?

Of course, would prefer not having to yank the manifold off of the boat to boil it or something drastic like that...

Any help or ideas would be appreciated.

[Don Moyer]

The shape of the cooling passages in the manifold make thems very difficult to clean once they become blocked to the degree that yours seem to be. Removing the freeze plugs is necessary to address the cooling jacket in the front area of the manifold (the part away from the engine). Otherwise, you will end up with a narrow channel along the top of the manifold between the
inlet and outlet fittings.

In my view, removing the manifold and taking it to a local machine shop would be the easier of the alternatives. The machine shop can remove the freeze plugs, hot tank it, and use acid as necessary.

We have opened the cooling passages in quite a few manifolds over the years in our shop by carefully pouring undiluted household muriatic acid directly into the manifold, letting it sit for 15 to 20 minutes and then pressure flushing. This is quite a difficult process while the manifold is still on the engine and the engine is still in the boat, but I suppose if you're very careful it's a possibility. You'll have to run the discharge hose directly overboard to avoid injury or damage to the inside of your boat.

Don

[Xestenz]

Thanks Don - both for the quick reply and for sharing your expertise with us.

I was afraid this would be the only course. Now, to start trying to wrangle those exhaust flange bolts off the manifold...

(Where are you, PB Blaster???)

- David

[Xestenz]

Success! Removed the manifold from the boat, and used undiluted muriatic acid poured into the passageways (gloves and eye protection mandated) that quickly removed to blockage with a pressure flush assist from a garden hose. Lot's of black gunk came out.

Went on to remove the freeze plugs, revealing a lot of loose scale chips and gunk down in the lower outside region of the manifold passages. When flowing water through to continue to flush I could see how these large flakes float up and easily block the passageways - something to think about for anyone with raw water cooling who experiences intermittant heat issues. Was able to break up and remove these flakes, allowing water to freely flow through all aperatures.

Gave the entire manifold a multi-hour diluted acid bath, and then did a final flush. Also removed and cleaned out the drain plug on the aft lower end.

Bad news was I sheared off an exhaust flange bolt in the manifold - resulting in an expensive bill at the local machine shop for a drill out and helicoil.

Working on getting the new freeze plugs to completely seal - although the seating ridges looked good still might need to resort to epoxy or JB weld there.

Thanks again for your advice, Don - should be back on the water now later this spring.