2GM20F Water Discharge

[MikeHoncho]

My 78 H30 was repowered with a 2GM20F. It has a water discharge to the starboard side of the exhaust. Water "pees" out the water discharge and exhaust. I haven't gotten to the very back of the boat yet ( to chase hoses and check on the rudder linkage). I've seen several videos of the same boat with the same motor without this water discharge. Input on why there would be a separate one compared to just letting it all go through the exhaust? It does have a new H2O heater with engine heat exchanger. Wonder if that is the reason. I got to do some exploring.

 

[Tally Ho]

My O’Day 322 has the same engine. I only have the exhaust pipe. Water and exhaust gasses combine at the mixing elbow and exit the exhaust.

Does your installation have 2 paths from the heat exchanger (mine only connects to the mixing elbow). Not sure what a water discharge is or how the water gets into that exit path.

Greg

 

[MikeHoncho]

Next on my list when I ferry back to the slip. I was wondering if it a confidence discharge so you can see you are pumping, like a outboard.

 

[heritage]

I had a Westerly that "peed" under the teak cockpit floor boards when the engine was running. It had a small diameter hose that was connected to the top of the exhaust riser, much like the anti syphon valves that are common today. But instead of having a valve at the top of a U shaped device, it let the exhaust water run into the cockpit. When the engine was shut down air would be drawn in and stop the possibility of syphoning. Could be what was rigged on your 2gm refit??

 

[Benny17441]

I have a feeling you are talking about an above the waterline exhaust discharge vs. the under the waterline discharge of newer models.

 

[MikeHoncho]

The discharge is a 3/4" thru hull that water only comes out. I'll get it figured out!

 

[kloudie1]

Here is a schematic of cooling water flow. Between the heat exchanger exit and the exhaust "ell" , there may be a vented loop .. your "telltale" water may be coming from the top of a loop, as Heritage says.. There are installations of a "hot" exhaust where the exhaust and water aren't mixed (exit separately), but the entire exhaust system would have to be metal and be insulated..

 

[SG]

The *. pdf diagram from Yanmar that was posted (quietly) by kloudie1 shows a "Mixing Elbow". That's the conventional installation for a variety of reasons.

The "mixing" combines the exhaust gases with the pass through raw water from you heat exchanger. There is usually a "can-like" muffler which located between the elbow and the discharge. That is often referred to as a hydra-lift muffler.

Assuming whoever repowered positioned everything properly in term of relative heights and plumbing, I think you should then have NOTHING else connected to that discharge. I think it best to have that above the waterline where you can conveniently check what's coming out visually in terms of relative volume and any smoke.

There are some boats that have a dry exhaust, but that's not very common for a bunch of reasons.

 

[MikeHoncho]

I'm going to get to the slip this week and check it out. I'll take pictures.

 

[MikeHoncho]

I had a Westerly that "peed" under the teak cockpit floor boards when the engine was running. It had a small diameter hose that was connected to the top of the exhaust riser, much like the anti syphon valves that are common today. But instead of having a valve at the top of a U shaped device, it let the exhaust water run into the cockpit. When the engine was shut down air would be drawn in and stop the possibility of syphoning. Could be what was rigged on your 2gm refit??

This is what it appears to be. Hose leaves the top of the heat exchanger and goes to a vacuum break loop secured about 1 feet above the engine and thru hull then goes to the exhaust riser. The thru hull is connected to the top of the vacuum break loop. The thru hull is about a foot above the waterline on the transom. It discharges water continuously while the engine is running. I'm concerned that to break the vacuum it has to clear out the approx 8 feet of 1/2" hose.

 

[jviss]

The thru hull is connected to the top of the vacuum break loop.

I would think that if the vacuum breaker was working properly, that water wouldn't come of of this.

 

[kloudie1]

I have seen installations where the top of the anti siphon loop had a small fitting, like 3/8", no check valve.. the small fitting had a hose going to a small thru hull so that when running it works like the telltale on an outboard motor.. The hose runs downhill without traps so that it empties when the water stops pumping.. plenty water goes to cool the exhaust and it does not take water away from the heat exchanger.. it shows that the pump is working.. Most folks can hear the exhaust "coughing" the water out which is a good indicator that the pump is working without having another hole in the hull..

 

[Charles Erwin]

What you describe is a darn good arrangement as long as the overboard discharge is not too large.

The overboard should be 'tee'd' into the loop below the anti siphon valve - on the motor side of the anti-siphon valve - not the exhaust side. If so - no vacuum is possible. You could actually eliminate the anti-siphon valve or leave it be if that suits you.

This arrangement also reduces possibility of overflow/hydrolock (if you have a non-start situation and keep the starter running too long) because seawater is pumped at relatively low volumes at starter RPM and that means most of it discharges via the overboard instead of filling the waterlock muffler - thence flooding back into the cylinder head.

Charles

 

[SG]

That’s assuming a very low volume in the up slope before the vent. You don’t want a slide back of water into the engine.

 

[MikeHoncho]

That’s assuming a very low volume in the up slope before the vent. You don’t want a slide back of water into the engine.

The vacuum loop is a good foot above the engine so I think that shouldn't be an issue.

 

[jviss]

Wow, I learn something every day. I had never heard of this.

 

[SG]

It’s the back flow. You don’t want too much volume flowing back. You should be okay.

 

[MikeHoncho]

Since we ste talking exhaust.... my exhaust is just below the waterline. I have a wakeboard boat with a fresh air exhaust system which is busy a Rd expensive turn down which forces the exhaust about a foot down into the water. Like a stinger. Although it works best at wakesurfing speed I was wondering if there would be any issue with putting on a longer exhaust turn down on mt H30. The diesel exhaust gets pretty bad with the Dodger windows up. It gets a stationwagon effect going