Gen set shutdown

I have the Borel temperature alarm bands that wrap around the wet exhaust, on both propulsion engines and on my genset. I also have a full set of gauges on the genie: water temp, oil pressure, volts, hertz & genset start battery volts. I do look at the gauges every now and again on the rare occasions the genset is running for any length of time.

Wet Exhaust Temperature Alarm by Borel Manufacturing Inc.

CaptTom said:

No
Yes. I have two of those already that I plan to install on the mains to let me know when it's overheating. I'll probably get one for the genset, too.

But I was also hoping to be more proactive and see if there was any way to monitor the coolant flow rate over time, rather than wait until it's too low to cool the exhaust.

As far as I can tell, the genset has been working fine the last few times I've run it. Hopefully all the gremlins that kept affecting coolant flow have been fixed. I just want to know if and when they come back.

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What make and model gen is it?

This is what you are looking for...
20064 Save Your Engine Kit - Detector, Panel & Buzzer [] - $93.00 : AQUALARM, Warning Systems For Land And Sea

High Wire said:

What make and model gen is it?

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An old Onan 75 MDJE-3CR. 7.5 KW. Cummins engine.

bligh said:

This is what you are looking for...
20064 Save Your Engine Kit - Detector, Panel & Buzzer [] - $93.00 : AQUALARM, Warning Systems For Land And Sea

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Not exactly. The whole point is, I don't want an alarm to tell me AFTER it's already overheating. My idea (and apparently not a good one, based on the response here and what's available in the market today) was to somehow monitor the flow from time to time, and spot a downward trend BEFORE it overheats.

CaptTom said:

An old Onan 75 MDJE-3CR. 7.5 KW. Cummins engine.



Not exactly. The whole point is, I don't want an alarm to tell me AFTER it's already overheating. My idea (and apparently not a good one, based on the response here and what's available in the market today) was to somehow monitor the flow from time to time, and spot a downward trend BEFORE it overheats.

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You will need some form of analog flow rate measurement AND indication to spot a trend of reducing flow. To be used in seawater, it would need to be a paddlewheel type or D/P cell with flow orifice, both of which are $$$. I can't think of any off-the-shelf indicator available. I think the Aqua Alarm flow switch will give you plenty of warning time to shutdown before the built in Hi Coolant Temp Shutdown occurs and way before damage occurs.
Also if the overheat problem originates from the engine coolant side, only a coolant temp gauge will show it before the shutdown occurs AND ONLY IF you happen to be looking at the gauge when the temp rise occurs. You would be lucky and/or a religious log taker to catch a slow temp rise failure.
A coolant temp gauge can be added pretty easily and is cheap.

CaptTom said:

An old Onan 75 MDJE-3CR. 7.5 KW. Cummins engine.

Not exactly. The whole point is, I don't want an alarm to tell me AFTER it's already overheating. My idea (and apparently not a good one, based on the response here and what's available in the market today) was to somehow monitor the flow from time to time, and spot a downward trend BEFORE it overheats.

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That is not correct. Once the seawater alarm goes off, signaling loss of seawater flow, it will still take time for the antifreeze to overheat. Before that happens, the genny will shut down on its own after the exhaust temp sensor realizes there is no water in it.
In reality, the switch will be good to ensure there is raw water flow every time you start your genny (or engine depending what mechanical systems you have).
This item is on my short list as I cannot verify raw water flow as all of my exhaust outlets are BWL.

High Wire said:

You will need some form of analog flow rate measurement AND indication to spot a trend of reducing flow...both of which are $$$. I can't think of any off-the-shelf indicator available.

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That's what I'm finding.

bligh said:

That is not correct. Once the seawater alarm goes off, signaling loss of seawater flow, it will still take time for the antifreeze to overheat.

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Which is exactly what I hoped to avoid.

My (obviously bizarre) theory was that if the flow stayed consistent at x GPH every time I ran the generator, then slowly started drifting down, I'd be able to do the repairs at my leisure, rather than in the middle of the night in a sweltering hot engine room at anchor somewhere.

But then it wouldn't be a boat, would it?

Sigh. I give up. I'll settle for a just-in-time warning alarm or two.

I think outboards and some I/O models have seawater pressure guages installed..may work..they aren't too much money and are pretty easy to install. (pic below)

The one thing about the water flow alarms is they don't sound when there's zero...there is a low limit that if the engine isn't at the pins for heat production...the engine stays relatively cool but the water flow is way off.

I think mine is set to alarm when the flow is below 3-4 gallons a minute which if the engine isn't screaming is enough.

Last lear at cruise, my aqual-alarm started to chirp ....no temp increase....finally it came on full a good 10 minutes after starting to chirp but me pressing on to make a dock rather than anchor in a narrow section of the ICW.

Turned out a large plug of seaweed and 3 peanut bunker fish had made it up my intake and were clogging the 1.5 inch line before the strainer basket.

So the aqua-alarms seem to be made that you will have a bit of margin before overheating...but maybe on a warm running genset...not as much as you would like. For long term monitoring...most people can judge a deteriorating impeller/housing from the exhaust water.

CaptTom said:

That's what I'm finding.

Which is exactly what I hoped to avoid.

My (obviously bizarre) theory was that if the flow stayed consistent at x GPH every time I ran the generator, then slowly started drifting down, I'd be able to do the repairs at my leisure, rather than in the middle of the night in a sweltering hot engine room at anchor somewhere.

But then it wouldn't be a boat, would it?

Sigh. I give up. I'll settle for a just-in-time warning alarm or two.

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Why not just change the impeller every 200 hours or annially like your manual says and don't worry about it?

PSNEELD, great idea. Water pump outlet pressure is an excellent indicator of water pump impeller health and overall changes to the flowpath. Simple and cheap!

psneeld said:

I think outboards and some I/O models have seawater pressure guages installed..may work..they aren't too much money and are pretty easy to install.

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Hmm. Now that might just work, thanks! My last boat actually had a water pressure display on the engine computer monitor, but I never really know what it was telling me.

bligh said:

Why not just change the impeller every 200 hours or annially like your manual says and don't worry about it?

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A good point to include here for the record. But I've actually changed them FOUR times in the past two seasons, so that's not really the answer. Only once did it make any difference. The overpriced aftermarket "run dry" high-tech impeller I bought, thinking I wouldn't have to worry about it all season, turned out to be a dud and actually CAUSED a near-overheat once.

As with the other times (not related to impeller failure), I detected the problem by climbing down on the swim platform to check the coolant flow visually. Very effective but not very convenient.

Needing to change an impeller often, i.e. short hours or time, is an indication something is wrong. Is the sea water draining out of the pump between uses? Is the flow to the pump restricted? Is the pump itself out of whack (technical term)?

Bay Pelican said:

Needing to change an impeller often, i.e. short hours or time, is an indication something is wrong. Is the sea water draining out of the pump between uses? Is the flow to the pump restricted? Is the pump itself out of whack (technical term)?

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I never said I needed to change it often. Every time I had to diagnose a problem, I checked the impeller first. Once apart, I figured I'd change it just so I don't have to worry the rest of the season. I actually introduced a problem one time because I installed what was advertised as a "better" impeller. It wasn't.

I changed a couple of impellers for a friend a couple weeks back and even though he double checked with the replacement provider, he looked it over and compared it with the old one, I looked it over and we installed it.

Of course it smoked and a second time we looked it over and tried it again.....

The only difference in the old and new impellers...was the inner cutout right around the shaft....it was just a 1/8 of an inch or so different...hard to see without knowing it, but it was hanging up and making the plate just a little too snug which was what was the real alert....but it wasn't so snug that it was way different from other impellers I replaced.

The real problem was that the tiny gap on the inside was enough that it wouldn't self prime....

The funny thing was the owner was just replacing these as a precaution to his upcoming sea trial. The original impeller for this genset had a few chewed up ends of fins and one totally missing. He was like wow....but it actually was pumping and cooling fine. We put it back in and the boat passed the sea trial...but he did mention the old impeller to the new owner.

I didn't see any obvious signs of impeller wear. But one good sign that the genny was getting warm was the exhaust starting to steam. It would run for an hour or two and then shut down. Obviously due to overheating. I did check it with a pyrometer but I really didn't see anything hot. All in the 150-160 range. But clearly the new impeller does pump more water.

Pierce said:

I didn't see any obvious signs of impeller wear. But one good sign that the genny was getting warm was the exhaust starting to steam. It would run for an hour or two and then shut down. Obviously due to overheating. I did check it with a pyrometer but I really didn't see anything hot. All in the 150-160 range. But clearly the new impeller does pump more water.

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I'm not familiar with your model, but you may consider checking your heat exchanger for buildup.

7KW Gas 3 banger Westerbeak

Pierce said:

7KW Gas 3 banger Westerbeak

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Like I said, I am unfamiliar with your westebeke, but I removed my heat exchanger a few months ago and lots of the cooling tubes were clogged restricting flow and subsequently cooling of the antifreeze. If you are unaware of the last time it was cleaned, its time to do it. Your manual should say where it is and how to access it. Hopefully they made it easy to access.