Exhaust Temperature Alarm

[dkirsop]

As part of my recent engine refit I decided to install a temperature alarm on the discharge elbow of my wet exhaust system. The temperature sensor is located downstream of where the seawater injection occurs. The purpose of the alarm is to notify me of any disruption in the sea water discharge before damage to the wet exhaust system occurs. The alarm provides both a visual and audible signal if the exhaust temperature exceeds 140 degrees F. Normal temperature is about 70 degrees F. at this location based on previous temperature monitoring. If the water flow is interrupted this alarm will sound long before the engine temperature gauge shows a problem. Following is a schematic of the system I came up with.

Alarm%20Schematic.jpg

The thermostat is a White Rogers, Fixed Setting, close on rise 140 Deg.F. with a 30 Deg. F. differential. The remaining items consist of a SPDT toggle switch, buzzer and indicator light.

Parts.jpg

Thermostatinfo.jpg

The thermostat comes with an eared mount which allows it to be clamped to the exhaust pipe with SS clamps.

Thermostat.jpg

I use dry transfer lettering to label the alarm system and switch positions on the dash. I have not been able to source this locally and order it on-line from Letraset in the UK. I use clear nail polish to protect the lettering once in place. The nail polish will dissolve the lettering unless applied carefully. The trick is to only apply a single light stroke and let it dry before attempting to apply more. Repeat as needed. In the photo below you can see where I rushed the process and a slight blurring occurs.

layout.jpg

Here is the finished installation. The buzzer is loud enough to be heard over the engine without being totally annoying. Best of all it can be turned off while you figure out what's wrong.

installation.jpg

[WillieC]

I am also installing a similar alarm if I ever get the engine back in. (Stuck on bottom paint right now, weather is not cooperating.) I wish you had posted before I bought the kit and paid too much, ah well. I will be using the same audible for low oil pressure and high coolant temp as well, as soon as I figure out where to place the diodes so only the offending warning light comes on under alarm condition.

I see with your schematic, you have to remember to flip the switch on when running. Any reason why you did not run it through the key switch? I like the test switch idea. With my half formed plan, the audible will sound because the low oil pressure will trigger it, since the engine is not running. Nice work, again.

[Beta Don]

I think the +12 volts in his schematic is from a key switched source

The 3 way switch is just a way to have a 'Test' mode and an 'Off' mode if you want to silence the alarm. Normally the switch would stay in the 'On' position 100% of the time

I've had raw water impeller failures a few times on several diesel boats that I've owned and I know almost instantly when there's no water in the exhaust system. The normally quiet 'burble' of the water cooled exhaust turns into a distinct, unmistakable, loud baritone when it runs dry. I've never seen the need for another alarm

Don

[dkirsop]

Don is right. I have a small fuse panel for critical engine systems that is keyed to the ignition switch. My engine circuits are completely isolated from my house circuits. So the switch controlling the exhaust alarm will normally be left on. My engine is only 2 cylinders and doesn't make a lot of noise so I am not sure I would notice any change in sound when running. The alarm simply provides me with peace of mind - until it goes off!

[WillieC]

Of course it is switched. I assumed and we all know how that goes. Too long under the boat and first grass cut of the season as well today. And then the rains return.
I agree with the importance of this alarm. I am adding the others for my peace of mind when I am not at the helm. Pesky gauges. Carry on!

[denchen]

I have nothing to do with the company, but NASA Marine in England have an exhaust temperature and warning gauge. Ive had one fitted to my A25 for a few years, and it works well. With the gauge showing the actual temperature, I can tell if the filter is starting to clog up with weed before it gets to the warning limit. The complete package is a fair price, and I have mine wired to the ignition key, so it goes on and off with the key.

NASA Temp.jpg

[sail149]

I defiantly think an exhaust temp guage is a great idea, I like the idea of numbers vs just a buzzer. I recently launched a small boat with 2 cyl westerbeke. I got to about 2/3 to the dock, about 3- 5 mins and relized somthing was wrong. I had been running the engine on the trailer to check everything. I think I checked the water flow before I left the dock but the exhaust is very low so I might have missed the lack of flow.
Don, yes the engine was sounding a little odd, but it was a windy day with a cross wind , I was checking other stuff and it took a while before I realized the engine sounded different from last year......nuts.
I throttled back and got to the dock with some coasting. Engine had not overheated on the gauge but it was worrying.
Sea cock was open , filter full but no flow. I don't know why the pump did not prime but some buckets of water in filter finally got it primed and I got water flow......BUT.....now I have to check the impeller which unfortunately takes quite a lot of dissemble to get at , oh well.......a guage could have helped here. I also want to be able to lend this boat and my Albin to family or friends.........I like the idea of an exhaust temp guage.....
Thanks for posting guys.
Cheers Warren

[DesertAlbin736]

Excellent suggestion. Here we go, another addition to the project list! Since we keep our boat dry stored on the trailer and launch and retrieve each time we go out, we close the raw water intake thru hull as we get ready to pull the boat out in order to prevent the raw water pump from losing prime. The exhaust elbow is up high enough that I've never seen water backflow in to the exhaust manifold, having recently pulled the elbow to inspect for corrosion. But the last time we went out I almost forgot to open the valve once we were on the water. An exhaust temp alarm would certainly be a good thing to have to warn of interrupted raw water flow before the engine actually overheated, since it can run for a short time without raw water flow just on the coolant that's on the fresh water side.

[DesertAlbin736]

"Sea cock was open , filter full but no flow. I don't know why the pump did not prime but some buckets of water in filter finally got it primed and I got water flow......"

We had similar issues when we first got our boat from the previous owner. They had rigged up a homemade funnel out of a Clorox bottle to prime the pump. In fact, the first chance we had to test run the boat was when we stopped at Lake Powell on the way home from picking up the boat from the previous owner's home in Idaho. They had a local lake nearby, but it was still closed for the season when we arrived in early March. So when we first put the boat in the water at the Wahweap Marina on Powell we couldn't get the pump to prime. Therefore we lost a chance to do a bit of cruising on Lake Powell.

First launch on Lake Powell, March, 2014. This dock was as far as we got, barely able to get back to the ramp without overheating.

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The problem was this old bronze strainer that happened to have a cracked sight glass, which gave me no end of fits.

Sea Strainer 001.jpg

Another problem was that the raw water hose leading to the pump had to route over the engine bed & make a loop, causing it to be prone to air lock. Due to space constraints there was no other way to route the hose.
The solution was to replace the old strainer with this Vetus unit, with added bonus that with the intake valve closed the top can be unscrewed to clean the strainer without disassembling the whole thing and needing to re-prime the systerm. That, and the inlet (black hose) and the outlet (red hose) are down lower. The top of the strainer is right about at the water line (the highest point practical to mount), so in effect it's self-priming. The inlet hose is double clamped, the through hull valve is under the small bilge pump strainer at lower right in the photo.

DSCN1991.JPG

[sail149]

To complete the story the pump impeller on the little Westerbeke was all torn up. I can only think the gasket on the 1970 strainer is letting air in and loosing prime in the inlet pipe. So I've got a new gasket 2 pack $15! Cork and rubber combo. I bought a gasket for the Albin's strainer too. I defiantly prefer the more modern style strainer with the large cap.
We will see. But the exhaust alarm should be a good idea .
Cheers Warren