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Old 11-05-2014, 04:21 PM   #1
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Exhaust Temp Warning devices

I need help sourcing snap-discs to make exhaust temperature warning devices for the exhaust elbows on my engines and genset. My understanding is that a bi-metal strip deflects under changes in temperature and makes/breaks an electrical circuit. Some forum members seem to have been down this path before. In another thread SteveH posted:

" . . . . purchased on Ebay a White-Rodgers snap disc (thermocouple), close on rise 180F, open on decline 160F. Attached it around the exhaust elbow with a SS hose clamp. At Radio Shack I purchased two LED lights and a piezo alarm. System powered through gen-set start switch. . . ".

I've searched on eBay, Amazon and Google - too much information, not enough understanding! Please point me in the right direction.
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Old 11-05-2014, 04:27 PM   #2
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Why not just buy the whole deal with something like Borel? Putting it together from bits and pieces will save at most a few dollars (and not boat dollars, either).
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Old 11-05-2014, 04:34 PM   #3
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Exhaust, Engine Monitors : AQUALARM, Warning Systems For Land And Sea

Look at their water flow alarms as well.

Borel as noted is another good source.

Wet Exhaust Temperature Alarm by Borel Manufacturing Inc.
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Old 11-05-2014, 05:42 PM   #4
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It does take some searching and knowledge to find the right snap-disc device. I bought a couple a number of years ago long before Amazon or Ebay from Grainger or McMaster Carr. You want a normally open device with a close temp of 160-180 F.

But last year when I decided to install an exhaust temp alarm I purchased the Borel alarm system. Glad I did.

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Old 11-05-2014, 06:59 PM   #5
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Quote:
Originally Posted by caltexflanc View Post
The first installation on any of my boats is an Aqualarm flow detector/alarm.
The big advantage is that the alarm sounds instantly on raw water flow failure.
Over temp alarms and bimetal alarms have to actually overheat before they activate ...... sometimes too late !
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Old 11-05-2014, 07:11 PM   #6
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Is the use of exhaust temperature warning devices common in recreational boats? If not, is there a demonstrated need? ... I don't have one.
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Old 11-05-2014, 07:50 PM   #7
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Get one!
And yes, they are quite common in the better makes. The engine you save could be your own!
Especially if you have a turbo, an EGT (Exhaust Gas temperature) gauge is also highly recommended.

http://www.bankspower.com/techarticl...t-is-important
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Old 11-05-2014, 08:07 PM   #8
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A few years ago I had a raw water pump throw a belt. The factory installed alarm is set to turn on at 195 degrees water temperature or low oil pressure. It functioned as advertised and I immediately shut the engine down with no fanfare and in plenty of time to avoid damage anywhere in the system. Six months later a surveyor conducting an insurance survey listed an exhaust mounted alarm as a safety issue. I subsequently discussed this with the insurance company and explained my earlier experience with the existing on board system. They agreed with me that the add-on would be redundant. I'm not sure if the surveyor misunderstood that a factory temp warning alert already existed, or if he made this recommendation as a matter of course. I believe it was the latter. Be sure that you're not already covered with a factory device.
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Old 11-05-2014, 08:50 PM   #9
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A water flow switch will give you a warning BEFORE your engine toasts your rubber exhaust hose. I've seen numerous overheated exhaust hoses (upon removal) that externally showed no signs but that had internally delaminated and "wrinkled" almost to the point of a 50% restriction. So,,, just how do you know your factory system worked if you have not inspected the inside of your exhaust.
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Old 11-05-2014, 08:57 PM   #10
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Quote:
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Is the use of exhaust temperature warning devices common in recreational boats? If not, is there a demonstrated need? ... I don't have one.
Impeller failure and the fast following pump destruction and melted exhaust hose and/or melted rubber or plastic muffler is very common. I deal with the claims all the time.
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Old 11-06-2014, 06:47 AM   #11
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Thanks all for the input. However, I still need a source for the snap-discs. I have the alarm buzzer, warning lights etc in stock. And no, my machinery has never had O/temp alarms.
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Old 11-06-2014, 08:20 AM   #12
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You might try calling Aqualarm or Borel and see if they will just sell you what you need. Such as this:

20250 Exhaust Overheat Detector [] - $39.00 : AQUALARM, Warning Systems For Land And Sea
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Old 11-06-2014, 08:42 AM   #13
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160 degree Thermo-Disc Fan Control Switch. | AmericanHVACParts.com
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Old 11-06-2014, 11:20 AM   #14
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The question has been asked: why do I need an exhaust temp (or raw water flow) alarm, won't the engine coolant alarm work?

Well yes if you have a Lehman, Perkins or similar chugging along at 1,600 rpm. But if you have a modern, high output, turbocharged engine, then you need the protection of a fast alarm. Here is why:

If you have a low powered engine putting out maybe 5-10 hp per liter then the heat rejected to the cooling system is relatively low and if you loose raw water flow then the coolant system temp will slowly rise, your alarm will sound and you can do something about it before any damage is done.

But some of us have the high output variety and we sometimes push them hard, close to 3,000 rpm where they are putting out 40-50 hp per liter. At that rate you are dumping much more heat into your cooling system. When you lose raw water the heat transfer is so great that you can overheat the pistons, melt the aluminum and "pick up" aluminum on the cylinder walls before the coolant temp gauge hits its alarm point.

And you don't have much time. If you aren't scanning your instrument panel like an airplane pilot you may miss the temp gauge rise and then it is too late when the alarm sounds.

I like use exhaust temp alarm like the Borel rather than the Aqualarm raw water flow sensor. But both work. Here are some pros and cons:

The exhaust gas temp sensor acts pretty fast but not as fast as the raw water flow sensor. It might take 5-10 seconds for the exhaust gas alarm to trigger at high loads, but that is fast enough. Temp sensors are very reliable- solid state thermistors. The Aqualarm is mechanical and relies on the movement of an internal paddle that could get fouled by sea growth and stick. But if it does stick it will indicate no flow and the alarm will sound so it should be a fail safe system. And you probably will hear it sound when you first turn on the ignition which is a good thing. The Borel alarm doesn't do this. It does have a way to test the alarm circuit but it isn't something that you can do routinely.

The Aqualarm flow sensor requires cutting the raw water hose at an appropriate point to install the sensor. The temp sensors wrap around the exhaust mixer so are much easier to install.

Every year I see several postings on boatdiesel of someone who overheated their engine when the belt broke, the strainer packed up, the impeller shredded, etc. and did serious internal damage. It is worth it to me to avoid that.

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Old 11-06-2014, 11:32 AM   #15
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The Newark catalog will have them. Search for bimetallic disc thermostats.
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Old 11-06-2014, 01:59 PM   #16
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The flow switch type is proactive, everything else is reactive. With a 370 hp 6BTA Cummins at full bore 10 seconds without water will destroy the exhaust system. It would probably take several minutes to put enough heat into the entire cooling system to cause the overheat alarm to activate. By then youve got way more problems than a hot engine.
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Old 11-06-2014, 02:52 PM   #17
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The exhaust temp sensor gets installed just downstream of the water injection point. No or very low raw water flow will heat the elbow up very quickly and close the switch. I think it will react in plenty of time.
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Old 11-06-2014, 03:39 PM   #18
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It "probably" will. Better than nothing anyway. Much better than relying on an engine overheat alarm.
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Old 11-07-2014, 09:36 AM   #19
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The flow switch type is proactive, everything else is reactive. With a 370 hp 6BTA Cummins at full bore 10 seconds without water will destroy the exhaust system. It would probably take several minutes to put enough heat into the entire cooling system to cause the overheat alarm to activate. By then youve got way more problems than a hot engine.
I suppose installing both would be best. If a hose breaks (say on the heat exchanger) you could have water flow but no engine cooling. And boat flooding as well.

On the other hand, if the engine or boat manufacturer though either of these was necessary they would have been installed at the factory. Just as with spare parts, it's hard to determine in advance what is likely to fail next.

I once did some maintenance and forgot to re open the seacock to the engine. After about ten minutes in a no-wake zone the overheat alarm sounded. I shut down the engine and ran below and opened the hatch. I realized right away what I had done, opened the seacock, ran back to the flybridge and restarted the engine (I was drifting back towards a bridge). The alarm soon stopped and everything was fine.
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Old 11-07-2014, 10:12 AM   #20
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I suppose installing both would be best...
We have both but as David pointed out, with our low rpm FL SP135, the flow sensor is first to alarm. Other than testing the snap disk, on the exhaust elbow, that has never gone off.
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