Volvo D2 55 - smoky exhaust, lowish water flow

[wingcommander]

I swapped out an 1/2 " skin fitting with scoop , for a 3/4 " whilst ashore this winter. The amount of crud that was trapped inside the scoop was surprising, Hopefully when I run her she will chuck out a tad more water from the exhaust . Easier to keep clean now no scoop is involved.
Legnth of hose to above waterline, open up and down with flexible drain brush .

 

[capnsensible]

I think you have a partially blocked saildrive inlet.

Saildrive. Well spotted.

Could try an acid product like, I think you call it there, brick cleaner. Dissolves dead stuff instantly. Finding a way to pump it down the saildrive might be a bit sporting though....

 

[dunedin]

I think you have a partially blocked saildrive inlet.

Per post #1 checking for that was where we started. Saildrive leg was rodded as usual when ashore less than a month ago, with very little being found, and have removed pipe and checked flow in at least twice as part of the diagnostics.
Flow fine at seacock - and per pst #16 reportedly when testing coming out of heat exchanger.

 

[Bobc]

Take the hose off the seacock. It should be like a fountain, about a foot in the air.

 

[robmcg]

BUT The water flow at the exhaust is still low and the exhaust steaming.

If the water is flowing through the heat exchanger and sufficient volume is reaching the exhaust elbow but the exhaust outlet volume is low then your exhaust hose is either delaminated internally therefore restricting flow or there is a blockage in the exhaust silencer.

 

[dunedin]

If the water is flowing through the heat exchanger and sufficient volume is reaching the exhaust elbow but the exhaust outlet volume is low then your exhaust hose is either delaminated internally therefore restricting flow or there is a blockage in the exhaust silencer.

Any idea how one could test for these ?

 

[Tranona]

If the water is flowing through the heat exchanger and sufficient volume is reaching the exhaust elbow but the exhaust outlet volume is low then your exhaust hose is either delaminated internally therefore restricting flow or there is a blockage in the exhaust silencer.

In that case the water would back up and fill the engine! Even if the hose was collapsed there is more than enough clearance for the water to get out. It is 50mm diameter and the inlet is 19mm!

 

[robmcg]

A partial delamination of the exhaust hose will restrict the water outlet through the exhaust. If you have a decent size silencer or a long exhaust run, it won't necessarily cause the flow to back up into the engine. Don't ask how I know.
I mention it as if your marine engineer is satisfied with the flow into the exhaust elbow but the exhaust outlet flow is poor, then logic dictates the problem exists between the elbow and exhaust skin fitting.
Checking is not that easy. An external visual inspection won't tell you anything. Maybe check the silencer first if it is accessible and see if anything seems amiss.

 

[Spirit (of Glenans)]

I think you have a partially blocked saildrive inlet.

This happened to me a few years ago. I was observing symptoms similar to those described by the OP. Various remedies were tried, as discussed in the posts above. I eventually discovered that the water inlet in the seacock was blocked. This was caused by the fact that I had habitually used a length of rebar, inserted through the hole at the bottom of the saildrive leg, to break up and remove the mussel shells which usually grow inside. It had worked fine over the years, but on this occasion it appeared that I had managed to ram fragments of mussel shell into the water passage, partially blocking the flow.
I was trying to remove the blockage while the boat was in the water, but rodding from above was impossible, as I could not get a wire or a drain snake to pass through the system, but I eventually cleared it by attaching a short length of hose to the seacock tail and blowing down it with the full pressure of my lungs.

 

[Bobc]

This happened to me a few years ago. I was observing symptoms similar to those described by the OP. Various remedies were tried, as discussed in the posts above. I eventually discovered that the water inlet in the seacock was blocked. This was caused by the fact that I had habitually used a length of rebar, inserted through the hole at the bottom of the saildrive leg, to break up and remove the mussel shells which usually grow inside. It had worked fine over the years, but on this occasion it appeared that I had managed to ram fragments of mussel shell into the water passage, partially blocking the flow.
I was trying to remove the blockage while the boat was in the water, but rodding from above was impossible, as I could not get a wire or a drain snake to pass through the system, but I eventually cleared it by attaching a short length of hose to the seacock tail and blowing down it with the full pressure of my lungs.

The way I've dealt with this previously is to remove the hose from the seacock, attach the dinghy pump, open the seacock, and pump hard a dozen times or so.