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Old 09-28-2014, 12:21 PM   #21
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Nope. That wasn't it either. Looks like I'm going to change the impeller next.
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Old 10-01-2014, 08:17 PM   #22
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Yep, that was it! Much more water coming out of the exhaust.
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Old 10-02-2014, 08:53 AM   #23
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This is one of two active generator raw water coolant threads on TF right now. I've had several near-misses with my Onan nearly overheating, with different causes each time. So I'm following these threads with interest.

There's good advice about impellers, heat exchangers, intake hoses, strainers and thru-hulls.

But I'm looking for an easy way to find out BEFORE it overheats. My current system is to climb down to the swim platform every 10 minutes and check the coolant flow coming out with the exhaust. Not convenient.

I plan to install one of those alarms that uses a sensor on the outside of the exhaust hose. A remote coolant temperature gauge would be good too.

Ideally, I'd like a flow sensor that I can glance at once in a while for peace of mind. Also, I could spot a longer-term trend of diminishing flow before it became a problem.

I haven't really found one that fits the bill. Most seem for larger systems or industrial process control, not monitoring my little Onan diesel.
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Old 10-02-2014, 12:44 PM   #24
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Does not your remote control panel have a coolant gauge?
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Old 10-02-2014, 01:26 PM   #25
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Does not your remote control panel have a coolant gauge?
Nope:


I do have room below this panel for some remote gauges. I'm thinking that a flow gauge would be more helpful than a coolant temp gauge. I could watch for any slow changes over time, and fix things before it got to the point where the jacket water was overheating. I've never seen this done, so maybe there's a reason for that.
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Old 10-02-2014, 03:30 PM   #26
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By remote panel I was referring to a Westerbeke remote display and control:

This is called the Admiral's Panel and is one of the more useful items you can have in terms of knowing what is going on with the generator.
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Old 10-02-2014, 07:37 PM   #27
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Nope:


I do have room below this panel for some remote gauges. I'm thinking that a flow gauge would be more helpful than a coolant temp gauge. I could watch for any slow changes over time, and fix things before it got to the point where the jacket water was overheating. I've never seen this done, so maybe there's a reason for that.
Does it have a coolant temp gauge on the genny? If so, temporarily relocate the gauge somewhere convienient above deck until you find the problem.
A high exhaust temp alarm is what you want long term. Here is a link to one:
Exhaust mixing elbow temperature
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Old 10-03-2014, 12:03 AM   #28
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Yep, that was it! Much more water coming out of the exhaust.
So what did the old impeller look like? Did you get all the pieces of the old one out?
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Old 10-03-2014, 10:10 AM   #29
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Does it have a coolant temp gauge on the genny?
No
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A high exhaust temp alarm is what you want long term.
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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Old 10-03-2014, 11:42 AM   #30
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Gen should have switches on both the exhaust mixer and in the coolant circuit. Should shut itself down if it overheats. These switches can be tested, but takes a little work.

Gauges are pretty to look at, but who is going to watch them to catch an overheat?

If you want to make sure cooling system is working ok, get an IR temp gun, load it up to the max and monitor engine temps with the gun.
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Old 10-03-2014, 02:33 PM   #31
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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.
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Old 10-03-2014, 03:04 PM   #32
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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.
What make and model gen is it?
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Old 10-03-2014, 04:28 PM   #33
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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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Old 10-03-2014, 08:49 PM   #34
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What make and model gen is it?
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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Old 10-03-2014, 09:28 PM   #35
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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.
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.
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Old 10-03-2014, 11:38 PM   #36
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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.
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.
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Old 10-04-2014, 07:43 AM   #37
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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.
That's what I'm finding.

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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.
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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Old 10-04-2014, 07:56 AM   #38
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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.
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Old 10-04-2014, 09:48 AM   #39
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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.
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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Old 10-04-2014, 09:49 AM   #40
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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!
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