hole in exhaust manifold

[mpohrille]

Strange story. I decided to remove my 50 yo copper standpipe exhaust to check it out. It turns out that it looks in good shape. I alos removed the manifold as an exhaust bolt broke off. Lo and behold the is a one inch by 1/2 inch hole on the inside of the manifold right below the exhaust gasket by the rear cylinder.

The mystery- this had to develop over several years. I have never noticed an exhaust leak or a cooling water leak. I can't explain it

As an aside when I took off the manifold there are six ports. Two on each end for exhaust and the two middle ones are for intake. Made me wonder hoe two intake ports in the middle of the block feeds four cylinders

[Dave Neptune]

The passages (runners) in the head combine the cylinders for the exhaust and intake to get to the manifold. Remember one single port carb is feeding all 4 cylinders and the "manifold" combines the exhaust to exit the manifold.

Sounds like a new manifold is needed. They do rust out eventually on raw water cooled engines.

Dave Neptune

[mpohrille]

Thank u for your explanation. I will need a new manifold. I don't think it makes a difference to the manifold if u r fwc (like on my boat) or raw water cooled. It is always raw water in the manifold

[joe_db]

Thank u for your explanation. I will need a new manifold. I don't think it makes a difference to the manifold if u r fwc (like on my boat) or raw water cooled. It is always raw water in the manifold

Not really. You can run fresh water through the manifold, I suspect almost all FWC engines do so.

[Dave Neptune]

If your FWC why would you NOT include the manifold as it is part of the engine that rusts out!
If you replace the manifold plumb it into the FWC and let the HX do all the cooling.

Dave Neptune

[mpohrille]

I am not understanding this. In a fwc system the antifreeze mixture circulates in the engine as a closed system, and raw water cools the antifreeze in the heat exchanger. The raw water is then pumped into the manifold where it cools the exhaust and then pumped into the muffler , either standpipe or waterlift. You could not pump out the anti-freeze as u have only about a gallon in the engine and it is a closed system

[Dave Neptune]

On an A-4 the exhaust and intake are one manifold and should be part of the closed loop via the crossover on top of the engine then to the HX. The HX is fed by the raw water pump and that raw water exits in the "exhaust stream" via an injection port.

Hope that makes sense.

Dave Neptune

[joe_db]

On an A-4 the exhaust and intake are one manifold and should be part of the closed loop via the crossover on top of the engine then to the HX. The HX is fed by the raw water pump and that raw water exits in the "exhaust stream" via an injection port.

Hope that makes sense.

Dave Neptune

I think this confusion comes from the many V8 inboard manifolds that use ports in the top of the manifold to feed the riser that then dumps into the wet exhaust, thus the engine block is FWC and the manifolds get raw water.
The better manifolds do not do this, the riser water injection is a separate inlet and the manifolds are part of the FWC circuit.

mpohrille : The A4 manifold is not connected to the water injection point directly, there is no need to make it part of the raw water circuit.

[mpohrille]

I am confused. Doesn't the cooling fluid injected into the manifold exit with the exhaust gases? So if u plumb it into your closed antifreeze system u would be constantly loosing fluid

[Dave Neptune]

M, what are you calling the manifold?

Fresh water (closed loop) starts at the coolant pump exits pump ten to the "tee fitting" (side of block) either into the block or "bypassed" to the top side of the thermostat housing where it mixes with the coolant from the block, there the coolant enters the "crossover" into the manifold then exits the manifold then to the HX and back to the pump repeat.

The raw water starts at the pump and goes t the HX and exits there to the exhaust system AFTER the manifold via an injection port and on out with the exhaust.

There is no mixing of exhaust and water in the A-4 manifold!

Hope this helps.

Dave Neptune

[joe_db]

[mpohrille]

Thanks for your patience with me. I just checked my manifold and c that there is a separate cooling jacket in the manifold. . For some reason I was confused and thought that raw water was being injected into the manifold

[joe_db]

Thanks for your patience with me. I just checked my manifold and c that there is a separate cooling jacket in the manifold. . For some reason I was confused and thought that raw water was being injected into the manifold

I had a boat with an engine that did that, but A4s do not.

[tenders]

This was a very legit question. I was second-guessing myself too! (I’m RWC.)

[mpohrille]

What a great community!!!!