What temperature should I set my exhaust alarm?

[FionaJC]

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.

[hlev00]

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.

[Wotname]

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.

[skipperpete]

Originally Posted by FionaJC

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?

[Wotname]

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).

[NorthCoastJoe]

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.

[mvweebles]

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/

[deblen]

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/

[skipperpete]

Originally Posted by Wotname

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.

[deblen]

Originally Posted by skipperpete

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

[roryboy]

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.