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Old 03-30-2014, 02:51 PM   #1
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Exhaust mixing elbow temperature

I want to fit gauges and/or alarms that will tell me if a mixing elbow is getting too hot. I am particularly concerned about the generator exhaust as it has a pretty blue silicone elbow just downstream of the seawater injection point (pic). Do you have such a monitoring system, and if so how does it perform? I seem to remember posts about using oven thermometers with remote gauges - any good?
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Old 03-30-2014, 05:47 PM   #2
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I like Borel Manufacturing's sensors and alarms. I've used this type of monitor on everything from a Donzi to my little Boomarang. Good stuff, works every time.

Wet Exhaust Temperature Alarm by Borel Manufacturing Inc.

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Old 03-30-2014, 05:53 PM   #3
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That's a nice looking little exhaust system. The silicon hose elbow is there because of it's high temperature resistance.

I plan on purchasing some of the items from Borel when I get back to my boat next week. Thanks for the link Larry.
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Old 03-30-2014, 06:15 PM   #4
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That's a nice looking little exhaust system. The silicon hose elbow is there because of it's high temperature resistance.

I plan on purchasing some of the items from Borel when I get back to my boat next week. Thanks for the link Larry.
Be sure to look at their home page. They make custom alarms to monitor other systems as well, in a compact, affordable package. They also have a navigation/anchor lighting panel that looks and works great.

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Old 03-30-2014, 06:43 PM   #5
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Good feedback. I recognized the product from other boats i had been on and was impressed. I plan on bilge alarms, exhaust temp and the nav light panel as I am designing and building an overhead console.

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Old 03-31-2014, 05:34 AM   #6
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Strongly recommend Boral from personal experience.
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Old 03-31-2014, 06:42 AM   #7
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Strongly recommend Boral from personal experience.
I have 2 that monitor my twins.
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Old 03-31-2014, 09:43 AM   #8
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I want to fit gauges and/or alarms that will tell me if a mixing elbow is getting too hot. I am particularly concerned about the generator exhaust as it has a pretty blue silicone elbow just downstream of the seawater injection point (pic). Do you have such a monitoring system, and if so how does it perform? I seem to remember posts about using oven thermometers with remote gauges - any good?
If your willing to go the n2k route there are numerous other options.

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Old 03-31-2014, 10:52 AM   #9
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On gennies and mains I use a switch with a setpoint around 180F and strap it on to mixing elbow with a hose clamp. I don't have the switch source readily at hand, but Borel should have them. I prefer these over sea water flow switches, as in my experience those have proven unreliable due to fouling.
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Old 03-31-2014, 11:59 AM   #10
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On gennies and mains I use a switch with a setpoint around 180F and strap it on to mixing elbow with a hose clamp. I don't have the switch source readily at hand, but Borel should have them. I prefer these over sea water flow switches, as in my experience those have proven unreliable due to fouling.
My experience as well. The industrial-quality snap switches are about as reliable as you can get, with almost no parts to fail, simplicity itself. I believe the Borel units are rated at 165F - 170F or so, but I have never had any problems with false alarms.

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Old 03-31-2014, 04:32 PM   #11
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Ski: fixing the temperature sensor directly onto the mixing elbow makes sense to me - that is the bit that gets hot first. To my surprise Borel's instructions specify that the temperature sensor be fastened to the exhaust hose. IMHO exhaust hose is probably a fairly good heat insulator, so by the time the outer surface of the hose reaches alarm temperature, the mixing elbow has been dangerously hot for some time and my little blue elbow would be long gone! What do you use to sound the alarm from your 180F switches?
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Old 03-31-2014, 05:02 PM   #12
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My experience as well. The industrial-quality snap switches are about as reliable as you can get, with almost no parts to fail, simplicity itself...I have never had any problems with false alarms.

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Old 03-31-2014, 05:47 PM   #13
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Ski: fixing the temperature sensor directly onto the mixing elbow makes sense to me - that is the bit that gets hot first. To my surprise Borel's instructions specify that the temperature sensor be fastened to the exhaust hose. IMHO exhaust hose is probably a fairly good heat insulator, so by the time the outer surface of the hose reaches alarm temperature, the mixing elbow has been dangerously hot for some time and my little blue elbow would be long gone! What do you use to sound the alarm from your 180F switches?
Not a simple question, really. Clamping on the mixer, once water flow stops the jacket becomes a void and heat transfer is poor. Attaching to the hose, heat transfer there is not very good either. I'm not sure which will pick up the heat first. Considering Borel's rep, I would defer to their instructions. They have probably tested in both places.

I used the mixer, partly because a SS clamp works well there, and also I use the mixer as the ground. Understood the limitations then, too.

I think either place works well enough.
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Old 03-31-2014, 07:19 PM   #14
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Not a simple question, really. Clamping on the mixer, once water flow stops the jacket becomes a void and heat transfer is poor. Attaching to the hose, heat transfer there is not very good either. I'm not sure which will pick up the heat first. Considering Borel's rep, I would defer to their instructions. They have probably tested in both places.

I used the mixer, partly because a SS clamp works well there, and also I use the mixer as the ground. Understood the limitations then, too.

I think either place works well enough.
I agree. Aqualarm makes a very similar alarm kit and state on their website "The Wet Exhaust detector has an aluminum band that adjusts from 2" to 8", making easy installation on the elbow or flexible hose." They supply 200F switches in their kits.

My Kohler diesel generator came from the factory with a temperature sensor on the mixing elbow that will shut it down if it gets too hot.

I don't think the location would matter much on a generator or small diesel, but I know for a fact that on high-horsepower Mercruisers, the hoses can overheat if there is reduced raw water flowing through the riser due to blockage or a failing pump. The flow is sufficient to cool the riser, but there is not enough water volume to mix with, and cool the exhaust gas at high power settings. The temperature downstream of the injection point can be significantly higher than the elbow itself. In these installations the mixing occurs in the hose, not the riser, so the band is best placed on the hose since it is the most susceptible to heat damage and failure.

Again, for our purposes, I would feel comfortable with either location.

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Old 04-01-2014, 01:32 AM   #15
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Bimetal Thermostats & Temperature Sensors - AIRPAX™ brand products: engineered, built and sold by Sensata Technologies

Either the 5003 or the 5004 series are the ones to use. Check out the temp range and pick one. They can be had form places like Newark Electronics, McMaster Carr.

All you need then is some wire, a BRIGHT led warning light and better a piezio alarm or two if you have a bridge.
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Old 04-02-2014, 06:49 AM   #16
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Some of what I am reading scares me.

At over about 140F i understand the salt comes out of solution and begins to coat the passages.

Sea water exhaust to a riser should be under the temperature where this happens, or failure is built in.
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Old 04-02-2014, 10:17 AM   #17
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Some of what I am reading scares me.

At over about 140F i understand the salt comes out of solution and begins to coat the passages.

Sea water exhaust to a riser should be under the temperature where this happens, or failure is built in.
That agrees with everything I have ever seen or heard. Most raw-water cooled marine engines operated in salt water have thermostats in the 135-143F range. 140F seems to be the norm.

As to risers, going back decades, yet still true today, the general rule is that the water cooled risers should never be too hot touch even after running. So what's that 110-120 maybe 130 max?

My Yanmar mixer elbow temperature after a hard 6-hour run was 109F measured with an IR heat gun first, then with my hand. My Kohler generator runs about the same.


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