Exhaust Temp Warning devices

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Shoalwaters

Shoalwaters

Guru
Joined
Feb 24, 2008
Messages
681
Location
St. Lucia, West Indies
Vessel Name
"Dragon Lady"
Vessel Make
DeFever 41
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 180ºF, open on decline 160ºF. 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.
 
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).
 
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.

David
 
Is the use of exhaust temperature warning devices common in recreational boats? If not, is there a demonstrated need? ... I don't have one. :confused:
 
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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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.
 
markpierce said:
Is the use of exhaust temperature warning devices common in recreational boats? If not, is there a demonstrated need? ... I don't have one. :confused:
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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.
 
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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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.

David
 
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The Newark catalog will have them. Search for bimetallic disc thermostats.
 
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.
 
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.
 
kulas44 said:
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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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.
 
rwidman said:
I suppose installing both would be best...
Click to expand...

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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rwidman said:
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.
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Ron,

In 2002 the ABYC included a requirement for these alarms in their publication P-1 INSTALLATION OF EXHAUST SYSTEMS FOR PROPULSION AND AUXILIARY ENGINES 7/02:

"1.7.1.4 An indicator shall be provided at all helm positions to indicate loss of exhaust system cooling water supply."

Also, most marine generators that I have encountered have an exhaust elbow/mixer temperature sensor in the safety shut-down circuit that stops the generator if it loses cooling water.

I have installed the Borel alarms on all of my boats for a while now, mainly because they are simple and trouble free. They can be tested with a hair dryer or heat gun, and I have found they react very quickly to increases in temperature. The response time is however directly related to the sensor placement and how quickly the mixer elbow and exhaust hose heats up when cooling water is reduced or interrupted.

In an attempt to protect the raw water pump in the event of a clogged intake or failed drive or belt, I have installed Speedseal Life covers to enhance run-dry capabilities while the alarms are being triggered or acknowledged. They make impeller changes much easier too.
 
It occurs to me after posting my last post that the best place for the flow sensor would be at the end of the raw water circuit, not the start. That would tell you that water was coming into the boat and leaving at the proper place.
 
LarryM said:
Ron,

In 2002 the ABYC included a requirement for these alarms in their publication P-1 INSTALLATION OF EXHAUST SYSTEMS FOR PROPULSION AND AUXILIARY ENGINES 7/02:

"1.7.1.4 An indicator shall be provided at all helm positions to indicate loss of exhaust system cooling water supply.".........
Click to expand...

I did not know that and my boat was built in late 1999. Are new boats being built with these sensors? I haven't seen posts on forums mentioning these before now.
 
rwidman said:
It occurs to me after posting my last post that the best place for the flow sensor would be at the end of the raw water circuit, not the start. That would tell you that water was coming into the boat and leaving at the proper place.
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That is an interesting idea, but how would the water flow sensor help in the event of restricted diminished flow? There might be sufficient flow to cool the exhaust at low speeds, but at higher engine speeds with reduced water flow you could still overheat the exhaust and the alarm would not sound.

On gas V-8 Mercruisers, we always installed a sensor on each bank. If one exhaust riser became clogged, you could quickly have an overheat situation because the cooling water could still exit through the other riser. Again, a condition where based upon water flow, everything would appear normal.

It's kind of like a chess game with the Devil or Murphy himself! :D
 
rwidman said:
I did not know that and my boat was built in late 1999. Are new boats being built with these sensors? I haven't seen posts on forums mentioning these before now.
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I don't think so. The ABYC guidelines are not a requirement for recreational boats sold in the US. It's my understanding that compliance is optional. Here is a good overview of this subject from the Nordhavn tech forum.
 
LarryM said:
That is an interesting idea, but how would the water flow sensor help in the event of restricted diminished flow? There might be sufficient flow to cool the exhaust at low speeds, but at higher engine speeds with reduced water flow you could still overheat the exhaust and the alarm would not sound.
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I'm not talking so much about overheating as water flow. Putting a water flow sensor at the beginning of the circuit (between the seacock and the raw water pump) would insure a flow of water to the pump but a broken hose could leave the pump filling the bilge with water without an alarm sounding. Putting the sensor at the last possible point in the circuit would insure water flow through the engine and out of the boat. Neither would detect an overheated exhaust system, you would need the heat sensor for that.

I think what holds me back from installing all these alarms is the mess of the extra wiring and all the aftermarket alarm panels (at both helms).
 
rwidman said:
I'm not talking so much about overheating as water flow. Putting a water flow sensor at the beginning of the circuit (between the seacock and the raw water pump) would insure a flow of water to the pump but a broken hose could leave the pump filling the bilge with water without an alarm sounding. Putting the sensor at the last possible point in the circuit would insure water flow through the engine and out of the boat. Neither would detect an overheated exhaust system, you would need the heat sensor for that.

I think what holds me back from installing all these alarms is the mess of the extra wiring and all the aftermarket alarm panels (at both helms).
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That is the reason I stopped after the exhaust temp alarm. At one time I wanted to have a custom Borel alarm panel made to monitor exhaust temp for both main and generator, high bilge water and the diesel filter water sensor. I looked at the amount of additional wiring and it wound up way down on my to-do list. I can't even imagine the same job with two helms, twins or both. Yikes!

It is very easy to get carried away with these kinds of upgrades and modifications. Our recreational boats are not airliners or space shuttles and don't require redundancy or sophistication found in those more complex systems. The technology is available though, if you want it and can afford it. I have to remind myself constantly to KISS and resist the urge to chase this stuff.:thumb:
 
Depends on the builder's philosophy about quality and safety. My 1981 Hatteras came from the factory with both exhaust temperature and engine temperature alarms.
 
caltexflanc said:
Depends on the builder's philosophy about quality and safety. My 1981 Hatteras came from the factory with both exhaust temperature and engine temperature alarms.
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Yep, that's where I stopped with this one. Engine temp gauge, engine temp alarm and exhaust temp alarm. That and good scan discipline of the panel when underway.
 
LarryM said:
Yep, that's where I stopped with this one. Engine temp gauge, engine temp alarm and exhaust temp alarm. That and good scan discipline of the panel when underway.
Click to expand...

That last discipline being the most important.
 
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