You miss the point somewhat.
Having the overheat temperature switch on the rubber exhaust hose, the first
thing to overheat with failure of seawater flow, while it does give me an early
heads-up on engine overheating, has the primary purpose of preventing damage to
the exhaust hose.
In my case, before installing this switch on the main engine exhaust hose, a
reduction of seawater flow due to a diverting valve opening by vibration (it is
tied off now) causing a reduction of water flow and subsequent overheating of
the inner liner of the exhaust hose which came loose from the carcass of the
hose and plugged up the rubber muffler increasing the backpressure in the
muffler until the muffler housing split apart on its flanged seam, opening the
muffler, and dumping a generous amount of diesel exhaust gas and oily, sooty
saltwater into the main berth area. (cool, a one-sentence paragraph)
We were on a Sunday cruise in Charleston harbor at the time. I had to shut
down, clean out the muffler, clamp it back together and then return to dock. I
spent the next several days replacing the expensive (5" x 20') hose,
permanently closing the split seam, and cleaning up the spectacular mess.
This would have been prevented if I had the little $10 switch on line. I did
just that before getting underway again.
The seawater strainer on the genset was added after bits of impeller vane
plugged up the heat exchanger and the fitting that sprays seawater into the
exhaust hose. The remedy required disassembly of all those parts for cleaning.
The strainer just downstream from the seawater pump has eliminated that work
in the future. On the upside, I discovered the iron exhaust elbow had rusted
out so I fabricated one from stainless which is still in good shape.
I actually have no seawater strainer on the main engine because the tranny
cooler is a coaxial type with just a straight pipe for the seawater flow and
the engine heat exchanger is just six bolts to open and clean. There is no
spray nozzle in that exhaust system to plug up.
Norm
S/V Bandersnatch
Lying Julington Creek FL
----- Original Message -----
From: Steve Weinstein
To: [email protected]
Sent: 1/29/2010 11:13:37 AM
Subject: Re: [Liveaboard] Transmission cooling mind bender
Great advice, as usual from your experiences, Norm! Thanks!
While I haven't had any of these problems - either on the old boat or this new
one - I like the concept since 1) my Yanmar panel just has idiot lights for
engine temp, and 2) there isn't any "control panel" for the genset. I know the
genset has an overheat thermocoupler or something on it which makes it shut
down above a certain temp so I'm good there. But I like the idea of the
redundancy of installing those thermoswitches on the exhaust hoses for the
engine and genset. At least I'd have an indication of the beginnings of an
overheat situation before the Yanmar idiot light and alarm kick in.
The additional strainer downstream of the raw water pump also looks like a
simple install and would be another way to see what's going on.....
Steve Weinstein
S/V CAPTIVA
1997 Hunter 376, Hull #376
Sailing out of Oyster Bay, NY
All outgoing mail protected by VIPRE A/V
----- Original Message -----
From: [email protected]
To: [email protected]
Sent: Friday, January 29, 2010 10:37 AM
Subject: Re: [Liveaboard] Transmission cooling mind bender
When remaking your main engine cooling system I suggest installing a water
strainer just downstream of the raw water pump. Connect it so that the water
enters between the transparent housing and the strainer so you can see any
debris in collected the strainer.
This will catch impeller bits before they lodge in the heat exchanger or riser
water injection nozzle. You will then be able to see when it is time to change
the impeller and will not have to clean out rubber bits downstream.
Doing this will save a great amount of work, thus greatly reducing the time
required to recover from a blown impeller, a Good Thing especially if one is
underway. (Trust me... )
While you are at it install a thermoswitch on the rubber main engine exhaust
hose. The exhaust hose is the first thing to get overheated when you loose
seawater flow. The main engine block has so much thermal inertia that it takes
a while for it to overheat so the hose may be destroyed (the inner liner cooks
and comes loose) before you are aware of a problem. (Don't ask me how I
know...)
It is a normally open switch, closing at 120 deg F, obtainable at a HVAC
supply. This switch is about a inch in diameter with two tabs to attach to a
duct and two 1/4" quick connect terminals. I hold it on the hose with a spring
around the hose hooked to the holes in the two tabs.
Do you have alarms on your engine? I recommend Murphy Gauges; these are gauges
with an adjustable contact to feed an alarm (or shutdown on a genset) circuit.
I have one for oil pressure and one for coolant temp.
Norm
S/V Bandersnatch
Lying Julington Creek FL
----- Original Message -----
From: JohnChristensen
To: [email protected]
Sent: 1/27/2010 10:32:54 AM
Subject: [Liveaboard] Transmission cooling mind bender
Hi everybody
I just put in a a new transmission. My engine is a Volvoi MD17C raw water
cooled the transmission is a MSB . I have however come up with a mindbending
issue and I would appreciate your input.
When I cleaned out the other transmission I found a old piece of impeller,
almost half a wing stuck in one of the elbows. This surprised me as the
transmission water to cool it is before the pump and the engine. I suspect
that the transmission cooling has been set up differently when the previous
owner had the boat
This brings up the point of what is the right order. As it is I have it set up
like this
Seacock Strainer- Water pump engine- riser-exhaust
I had a lot of scale in the old transmission and considering a piece of
impeller as well it is a wonder how water came through it.
I am considering a different order, actually 2 different ways.
1.Seacock- Strainer- Water pump Transmission Engine- Riser- Exhaust
Either that or
2 . Seacock- Strainer Water pump T - (one end of the T to the engine the
other to the Transmission) Riser and T to transmission for the exhaust
This would eliminate scale build up in the transmission restricting cooling of
the engine.
In the manual the water is routed from the seacock to the transmission then the
pump, but that seems wrong, what do you think
Regards John
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To search the archives http://www.mail-archive.com/[email protected]
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