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Old 30-04-2024, 16:58   #1
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What temperature should I set my exhaust alarm?

I have a Perkins 4107 with a Bowman heat exchanger. Many years ago on another setup I suddenly had no raw water flow and I didn't notice. It melted everything and filled the boat with exhaust fumes.

I now have an alarm for the flow into the engine and an exhaust temperature sensor. These both feed into an engine monitoring system with alarms.

My question is, at what temperature do I want to hear the alarm? I have seen various answers but I wonder if someone out there can tell me the definitive answer in either Celsius or Fahrenheit.
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Old 30-04-2024, 17:44   #2
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Re: What temperature should I set my exhaust alarm?

In case no one provides an answer from experience, maybe head out for a sea trial and try some different settings to see when the alarms fire.
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Old 30-04-2024, 18:07   #3
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Re: What temperature should I set my exhaust alarm?

The Vetus exhaust temperature alarm sensor activates 71C (160F).
https://vetus.com/wp-content/uploads...armsysteem.pdf

That said, if your exhaust temperature is significantly lower, you could set it lower.
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Old 30-04-2024, 20:45   #4
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Re: What temperature should I set my exhaust alarm?

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I have a Perkins 4107 with a Bowman heat exchanger. Many years ago on another setup I suddenly had no raw water flow and I didn't notice. It melted everything and filled the boat with exhaust fumes.

I now have an alarm for the flow into the engine and an exhaust temperature sensor. These both feed into an engine monitoring system with alarms.

My question is, at what temperature do I want to hear the alarm? I have seen various answers but I wonder if someone out there can tell me the definitive answer in either Celsius or Fahrenheit.
There’s no definitive answer, some wet exhausts run pretty hot at high rpm and need silicon hoses and stainless steel aqualocks but a perkins 4-108 at full power would warm up to around Wotties suggested 70°C. Most of the time even at max output I can put the inside of my wrist on the flexible hose between the mixer elbow and the aqualock but my coffee cup at drinking temp is a bit too hot to comfortably do the same test….60°c is how I like my coffee.
Have you got a “Murphy swichgage” to monitor the wet EGT ? If so , what temps are you seeing on the gauge?
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Old 01-05-2024, 00:12   #5
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Re: What temperature should I set my exhaust alarm?

As a very rough rule of thumb, 50C (120F) is the temperature that is too hot (for your hand) to touch. It is also the temperature that red meat protein (myosin) starts to denature (cook); it follows that if something is too hot to touch, it is hot enough to start cooking your hand and is equal or greater than 50C (120F).
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Old 01-05-2024, 14:29   #6
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Re: What temperature should I set my exhaust alarm?

I would have to think every setup is a little different. On my boat I am setting up an exhaust gas temperature gauge ( pyrometer ). With that I can see the engine loads and go from there. Where is the alarm placement? Is the sensor in the exhaust flow or mounted to the outside of the hose or exhaust elbow?

If you can borrow or buy a non contact thermometer I would do some runs under normal conditions and do some readings where you want to mount the sensor. I found with a dirty prop and bottom my exhaust temps went sky high prior to the water induction point. But even at that level I could put my hand on the exhaust hose. Measuring EGT is a good indicator of how hard the engine is working.

For an alarm temp you need to know your normal values first. Maybe start at a lower temp than you think you need and bump it up until you stop getting an alarm, then add in a few degrees to your set point.
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Old 01-05-2024, 16:23   #7
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Re: What temperature should I set my exhaust alarm?

Answers here partially explain why sailors don't trust their engines. They don't know what they don't know. I love the observation that seems to recommend duct-taping a NY Strip steak to your exhaust and if it cooks beyond rare (120F), it's too hot. Right out of a Monty Python movie......

For $80, get a Borel alarm. Zip tie the sensor to your wet exhaust line. I forget if it alarms at 160F or 165F, but if you lose water flow, you'll know.

https://www.borelmfg.com/product/sin...w-water-alarm/
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Old 01-05-2024, 16:59   #8
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Re: What temperature should I set my exhaust alarm?

I have had a Borel for 15yrs. Strapon sensor goes around my rubber exhaust hose approx 6-8" after engine exhaust elbow.-Volvo Penta 2003
The specs say it is factory set to alarm above 75C/167F
https://www.borelmfg.com/wp-content/...rawPDF3-19.pdf


https://www.borelmfg.com/
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Old 01-05-2024, 21:21   #9
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Re: What temperature should I set my exhaust alarm?

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As a very rough rule of thumb, 50C (120F) is the temperature that is too hot (for your hand) to touch. It is also the temperature that red meat protein (myosin) starts to denature (cook); it follows that if something is too hot to touch, it is hot enough to start cooking your hand and is equal or greater than 50C (120F).
Haha, last week in Bangkok they had high 53°C temp index… that’s not actually 53°, its a “feels like 53°” and the actual temp in the heatwave was below 45° but its still bloody hot. I’m in Langkawi at the lower end of the heatwave area with nothing above 38°C but humidity at 94% and even this relatively low temp feels life threatening…. My car is too hot to touch by A LOT, my phone goes into survival mode and shuts down. The Saudi tourists come here for holidays to escape the heat in their own country, apparently they get the real 50°C over there, not the “feels like” and yes, I believe its possible to get cooked here…. More like Sous vide than oven cooked BUT, cooked none the less. The upside is that my coffee takes a long time to cool off….. unless I’m in a chilly Starbucks.
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Old 02-05-2024, 07:35   #10
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Re: What temperature should I set my exhaust alarm?

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Haha, last week in Bangkok they had high 53°C temp index… that’s not actually 53°, its a “feels like 53°” and the actual temp in the heatwave was below 45° but its still bloody hot. I’m in Langkawi at the lower end of the heatwave area with nothing above 38°C but humidity at 94% and even this relatively low temp feels life threatening…. My car is too hot to touch by A LOT, my phone goes into survival mode and shuts down. The Saudi tourists come here for holidays to escape the heat in their own country, apparently they get the real 50°C over there, not the “feels like” and yes, I believe its possible to get cooked here…. More like Sous vide than oven cooked BUT, cooked none the less. The upside is that my coffee takes a long time to cool off….. unless I’m in a chilly Starbucks.

That temp would kill & cook a Canadian./L
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Old 02-05-2024, 08:10   #11
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Re: What temperature should I set my exhaust alarm?

Borel Manufacturing (R) has been manufacturing exhaust alarms for decades. They use a fixed set point of 75° C / 167° F. These are simple thermistors strapped to the rubber hose.
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Old 25-01-2025, 22:36   #12
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Re: What temperature should I set my exhaust alarm?

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The Vetus exhaust temperature alarm sensor activates 71C (160F).
https://vetus.com/wp-content/uploads...armsysteem.pdf

That said, if your exhaust temperature is significantly lower, you could set it lower.
Hi Wotname - I'm curious. How do you set it lower? I don't see any such ability with this setup.

I've had a real challenge with the Vetus sensor (today!). I wanted to test it before drilling a hole in my exhaust and I found that I could not trigger the alarm. I could jump the two connectors and the alarm would buzz - this tells me that the wiring setup is good - but a heat gun and a cup of near-boiling water applied to the sensor gave me nothing. I'm going to play with the ohm meter tomorrow. I think I would prefer a combination alarm plus a temperature gauge simply to show that the sensor is working at all.

Thanks for all of the great comments on this thread.

Greg
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Old 26-01-2025, 19:14   #13
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Re: What temperature should I set my exhaust alarm?

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Hi Wotname - I'm curious. How do you set it lower? I don't see any such ability with this setup.

.......
Hi Greg, you are correct in that the Vetus exhaust temperature sensor is not adjustable. The only way to have a different set temperature is to use an non-Vetus sensor.

These temperature sensors are a simple ON/OF switch and industrial units can be found with a variety of operational temperature set points. You do have to work out how to fit it into your exhaust system.
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Old 26-01-2025, 22:00   #14
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Re: What temperature should I set my exhaust alarm?

I've just tested 2 different Vetus sensors and had no luck in triggering them. I used a multimeter and put the sensor in 200 degree water. Zilch. I'm suspicious that these things work at all. I'm going to pivot to a Borel or Aqualarm. FYI and Thanks.
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Old 27-01-2025, 06:38   #15
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Re: What temperature should I set my exhaust alarm?

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I've just tested 2 different Vetus sensors and had no luck in triggering them. I used a multimeter and put the sensor in 200 degree water. Zilch. I'm suspicious that these things work at all. I'm going to pivot to a Borel or Aqualarm. FYI and Thanks.
The circuit board on the back of the engine control panel has several potentiometers to set alarm thresholds.
Adjust with an alignment tool (plastic screw driver)
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