Manifold termonology and how the heck it works

[Nebfarmer]

AQ470A. I would like to understand how watercooling the exhaust works without filling the cylinders with water when the engine is shut off. Also what are the risers? Also whats the oil viscosity requirements of this engine? Seloc manual not much help. TIA

 

[skydiveD30571]

Re: Manifold termonology and how the heck it works

The risers are the parts on top of the manifolds that travel straight up. Then there's an elbow that turns towards the stern and attaches to the exhaust piping that travels to the transom. Exhaust gas travels up the center of the manifold and riser, and water travels up channels surrounding the center channel. So they are separate at this point and the water is used for cooling. They mix at the top of the riser by the elbow. So when the engine is shut off water shouldn't be traveling through the exhaust channel towards the cylinders unless a gasket is bad, dieseling, or some other cause of water being rapidly ingested back though the exhaust system.

Oh and get rid of the Seloc manual and get an OEM service manual.

 

[Fleetwin]

Re: Manifold termonology and how the heck it works

The riser(s) act like a an upside P trap that you would see under your sink.

The cooling takes place by having a tube inside a tube. The exhaust travels through the inner tube and the water travels through the outer tube. They are not supposed to meet until both get to the riser(s).

 

[Nebfarmer]

Re: Manifold termonology and how the heck it works

Thanks for the explanation. Been having a water problem in the right bank. I found a area that looked like it could be leaking between the riser and the riser extension. When I surfaced it the problem really showed up. The gaskets looked new, supposed to be a fresh overhaul, and were reinstalled with red permatex until the new ones get here. 10-4 on the sealoc manual but where can I get an OEM for an 1990 AQ740A? Glad it's a freshwater boat .

 

[JoLin]

Re: Manifold termonology and how the heck it works

At the V-P store

Gasoline Engine Manuals - Volvo Penta