Exhaust Temp Sensor vs Raw Water Temp Sensor

Our boat is a 2007 34' Mainship Pilot with the Yanmar 370 hp engine. I am planning on installing a raw water temp sensor, but not sure if an exhaust temp sensor would be better. If I get the exhaust temp sensor do I even need the raw water sensor? Or, do I need both? Looks like Borel makes the sensors. Any other model sensors that you recommend? Thanks for your expertise!!

The advantage of a raw water discharge alarm is to notify you of an impeller failure or plugged up sea strainer, forgot to open the hull valve.
In theory, the alarm temp is set low enough so as to give you time before eating another impeller or other damage.
There is one company, to my knowledge, that makes an add on unit. I have two until, in the storeroom, waiting to be installed. One for the main engine and one for the generator.
I have looked for any notes I might have but, none available. I have to go to the storeroom soon. I shall try to remember to bring them back.
Injection temp is nice incase a MOB. A low temp does have a way of motivating a faster recovery.

I have the Borel system and love it. Simple to install. I have exhaust alarms on both main engines and genset. Also two high water alarms and witer in fuel for the mains.

Comodave said:

I have the Borel system and love it. Simple to install. I have exhaust alarms on both main engines and genset. Also two high water alarms and witer in fuel for the mains.

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Yup. That's system I was suggesting. Thanks Dave. Now there is on urgency to go to the storeroom.

Being belt and suspenders I have a raw water flow sensor before the engine water pump and a exhaust high temp after the mixer. Hope one or both will give me enough warning to shut down before damage is done.

I am hesitant to add anything that could screw up the raw water intake. Just one more possible failure point. I added the exhaust temp warning.

Easting said:

I am hesitant to add anything that could screw up the raw water intake. Just one more possible failure point. I added the exhaust temp warning.

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The Borel system consists of large hose clamp, a temp sensing device and a read out. No holes except where to mount the read out display.

There is a raw water flow alarm, made by Aqualarm and an exhaust gas temp alarm made by Borel. Wasn't aware that Borel also had a r/w temp alarm.

I had that same boat and engine and installed the Borel raw water temp alarm on a Centek fiberglass connector just after the blue hump hose below. It was too sensitive there and sometimes alarmed on hot days near idle. I moved it downstream a couple of inches over the black hose and that stopped the spurious alarms. But those spurious alarms were convincing evidence that it worked.

See the attached pic which describes my setup. BTW I installed the connector as part of a riser extension to avoid water backing up into the turbo.

A raw water temp alarm would possibly alarm too late and may allow low raw water flow to exist for a long time. A raw water flow alarm like Aqualarm may stick and therefore fail to alarm.

All in all I like the Borel exhaust gas temp alarm.

David

When I switched from sail to our Tug, I was worried about the raw water flow. On the sailboat, I could see and hear the water flowing and therefore, was comfortable that cooling was at least happening. (I know that seeing the flow may not be totally adequate, but at least there is some flow - seacock not closed).
On the tug however, the flow exits under the boat and it is very, very difficult to know for sure that there is any flow.
So I installed an Aqualarm raw water flow alarm in both the main engine and the gen set (between the strainer and the raw water pump). It alarms instantly if flow is blocked or reduced to a level of concern. My gen set "sucked in a small fish" once and this alarm sounded and "saved the day". I shut it down before the overheat could occur or before the impeller was damaged. Clearing the fish, however, required a swim (not fun).
I also installed on both engine and gen set exhaust temp alarms. Here I chose Borel brand as they alarm at a lower temp than the Aqualarm brand, and an earlier warning is important.
Well, guess what. On our first trip after bringing the boat home (from the purchase), the main engine exhaust alarm sounded. I investigated engine temps "all over the place" using an IR temp gun, and all was very good except for one "hotspot" on the exhaust hose. This puzzled me (and a couple of mechanics I talked to) and I decided since it was a "new to me" boat, that I would service the entire raw water cooling system to gain a baseline. The cooling system was in good condition except I discovered that my "doomed to fail" exhaust elbow (see sbmar.com to learn about this) had started to fail (internal leak), was not mixing the water and gases properly causing the overheat on the hose. This situation could have (if not discovered) allowed raw water to enter the turbo or even the exhaust side of the engine. I caught it in time to avoid MAJOR damage only because of the exhaust hose alarm. Turns out to be the best $100 bucks I have spent!!
I have it from very reliable professional sources (such as Tony Athens) that if you rely on the "normal" coolant overheat alarm, it is very possible that you will do engine damage before that alarm goes off to warn you! The exhaust alarm will give enough warning to throttle back and or shut down before damage occurs and in my case saved me from big problems (at least potentially).
These alarms are inexpensive (about $100 each) and are easy to install. With them in place you will know BEFORE damage can occur if you left the seacock closed, sucked in a thru hull blockage, had an impeller failure, or are about to suffer an engine overheat from any other of multiple causes.
Personally, I don't know why they aren't "standard equipment".
Disclaimer: I am not affiliated with any of the above mentioned companies or people, just a customer.

Just my humble opinion,
Tom

The Borel system is so easy to install. It does not require any modifications to the water system. It has a sensor that is basically a large tie wrap that goes around the exhaust hose after the cooling water is injected. It should alarm much quicker than an engine temperature gauge since the exhaust will become very hot if the cooling water flow is interrupted.

Comodave said:

The Borel system is so easy to install. It does not require any modifications to the water system. It has a sensor that is basically a large tie wrap that goes around the exhaust hose after the cooling water is injected. It should alarm much quicker than an engine temperature gauge since the exhaust will become very hot if the cooling water flow is interrupted.

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Like Comodave,
I feel the Borel system is almost a necessity. An overheat will show up in the exhaust hose first, in most cases.

However, to ensure that this alarm is functioning properly (and not just giving a false sense of security), it must be periodically tested by using the "test wires" that are part of the unit.
The water flow alarm is really just a "paddle" inside the sensor that moving water pushes up out of the way and in effect "shutting off" the alarm. It self tests every time you start the engine. As soon as the ignition power is turned on the alarm sounds as the "paddle" is down and "blocking flow" if you will in "alarm position". As soon as the engine starts and water is flowing, the paddle is pushed up out of the way and the alarm stops! You would know right away if it does not silence after the engine starts, as either the paddle did not move (malfunction) or there is no water flowing (seacock closed or thru hull blocked, for example by a plastic bag). This alarm (water flow) has not reduced my cooling effectiveness one bit. I would suggest that "lack of maintenance" (meaning leaving it longer than say 2 years) of the raw water cooling components would have more of an affect.


For example, in my earlier post (2 above) when my gen set "sucked in" a fish. If not for my water flow alarm, I might have had the impeller self destruct and then I would have had to not only remove the dead fish, but I would have had to replace the impeller and find all of the impeller bits in the heat exchanger. The water flow alarm instantly went off when water stopped, and I shut down within a few seconds. No damage, no additional work!


I am convinced that a combination of both types of alarm give a more complete protection and piece of mind!!
However, each to his own and "whatever floats your boat"

How does the Borel raw water sensor work?

Thank you all for the replies but I'm hoping you can help me understand how these things work. My understanding is that the Borel is a temp sensor set to 165 degrees. Regarding the raw water side, if you install this between the strainer and water pump, will the sensor be monitoring the temp of the raw water, which wouldn't this be the temp of the raw water coming in from the waters you are boating in? Say 80 degees on average? Am I missing a cooling loop somewhere where the water would get hot before the water pump? On the exhaust temp sensor, Borel said they do not, or no longer make a specific exhaust temp sensor. Are you guys using the same Borel sensor for the exhaust as you are for the raw water? If so, and it is installed right after the exhaust mixing elbow, isn't the temp going to be hotter than 165 degrees? I think I have a 180 degrees thermostat but not sure if the two are related. I checked out the aqua raw water alarm and the paddle makes sense for monitoring flow but agree it is another failure point. Thanks for helping me understand this!!

sammy999 said:

Thank you all for the replies but I'm hoping you can help me understand how these things work. My understanding is that the Borel is a temp sensor set to 165 degrees. Regarding the raw water side, if you install this between the strainer and water pump, will the sensor be monitoring the temp of the raw water, which wouldn't this be the temp of the raw water coming in from the waters you are boating in? Say 80 degees on average? Am I missing a cooling loop somewhere where the water would get hot before the water pump? On the exhaust temp sensor, Borel said they do not, or no longer make a specific exhaust temp sensor. Are you guys using the same Borel sensor for the exhaust as you are for the raw water? If so, and it is installed right after the exhaust mixing elbow, isn't the temp going to be hotter than 165 degrees? I think I have a 180 degrees thermostat but not sure if the two are related. Thanks for helping me understand this!!

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You have misunderstood the Borel alarm. It measures the temperature of raw water used for cooling the engine right at the endpoint of that cooling system, which is just after raw water has been used to cool down hot exhaust gases so they can be safely discharged overboard. The alarm works via a temperature sensitive electrical connection within a metal band installed around the exhaust hose immediately downstream of the raw water/hot gasses mixing elbow. Being at the end of the cooling chain, any restrictions or losses of raw water earlier in the chain are detected. The raw water FLOW alarm, on the other hand, is typically installed immediately after the raw water pump to detect a raw water Intake blockage or pump failure. While this is very useful, a problem arising after the paddlewheel sensor (heat exchanger failure or hose leak for example) Is not detected by the upstream flow alarm. I agree with the earlier response that a Borel alarm is practically a necessity. The paddlewheel type flow alarm is a nice to have....and itself requires some maintenance and checking.

I’ve been considering an EGT sensor/alarm as well. As someone noted, Borel doesn’t seem to offer them anymore. This kit is a little more intrusive, requiring a penetration in the exhaust elbow. Does anyone use these or something like them?

EGT Digital PMD1XT Pyrometer Gauge + Probe Kit - Diesel Race Series DF

angus99 said:

I’ve been considering an EGT sensor/alarm as well. As someone noted, Borel doesn’t seem to offer them anymore.

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Huhhh! See Wet Exhaust Temperature Alarm by Borel Manufacturing Inc..


Yes it is an external sensor that measures the temperature of the hose and alarms when it hits 165 F, and is not directly in the exhaust gas path. But you don't want that, both for corrosion and temperature stability reasons.


I will bet that more marine engines have been saved with the Borel alarm than any others including standard engine gauges.



David

sammy999 said:

Thank you all for the replies but I'm hoping you can help me understand how these things work. My understanding is that the Borel is a temp sensor set to 165 degrees. Regarding the raw water side, if you install this between the strainer and water pump, will the sensor be monitoring the temp of the raw water, which wouldn't this be the temp of the raw water coming in from the waters you are boating in? Say 80 degees on average? Am I missing a cooling loop somewhere where the water would get hot before the water pump? On the exhaust temp sensor, Borel said they do not, or no longer make a specific exhaust temp sensor. Are you guys using the same Borel sensor for the exhaust as you are for the raw water? If so, and it is installed right after the exhaust mixing elbow, isn't the temp going to be hotter than 165 degrees? I think I have a 180 degrees thermostat but not sure if the two are related. I checked out the aqua raw water alarm and the paddle makes sense for monitoring flow but agree it is another failure point. Thanks for helping me understand this!!

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Sammy,
You have two sides to your cooling system. The Coolant side (antifreeze with freshwater) and the raw water side. They do not mix, but do come in contact for heat exchange purposes in the various heat exchangers. It does not matter a great deal what temperature the seawater coming into the engine is so you do not need a temperature alarm there. The Borel exhaust hose alarm band measures the temperature of the raw water after it has been mixed with the engine's exhaust gases. The usual temperature here (in the exhaust hose) with a system working well ranges from 100 to 120 degrees F. hence the 165 degree alarm point. If you cannot get a Borel? then Aqualarm makes one that alarms at 180 degrees (a bit later warning but still good). As stated by David, this alarm has saved more engines from damage because by the time your coolant side goes into alarm, the engine has overheated and damage may have already occurred.
If you have an exhaust alarm installed, the water flow alarm (is a backup from an engine overheat point of view) will possibly "save" your raw water pump impeller if you forget to open the seacock or the water intake gets plugged by some debris or as in my case explained earlier a fish were to somehow get in there and block the passage.

An exhaust gas temperature sensor will tell you what the engine load is doing. The Borel alarm is aimed towards the water flow and not the exhaust gas temperature function. The Borel will tell you almost immediately if you loose cooling water flow. The exhaust gas temperature sensor is mounted before the cooling water is injected into the exhaust. It can tell you if you are overloading the engine but not if you loose cooling water flow.

Comodave said:

An exhaust gas temperature sensor will tell you what the engine load is doing. The Borel alarm is aimed towards the water flow and not the exhaust gas temperature function. The Borel will tell you almost immediately if you loose cooling water flow. The exhaust gas temperature sensor is mounted before the cooling water is injected into the exhaust. It can tell you if you are overloading the engine but not if you loose cooling water flow.

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Comodave,
Are you confusing the Borel exhaust hose alarm (just a band) that IS installed on the exterior of the engine exhaust hose AFTER the water injection point with a pyrometer that is installed (near the turbo if there is one) and the exhaust temp is actually measured PRIOR to the water injection point? The Borel band cannot measure engine load as it is simply an overheat alarm. If the hose temp goes above the set point, the alarm goes off, meaning investigate now, there is a problem.

firehoser75 said:

Comodave,
Are you confusing the Borel exhaust hose alarm (just a band) that IS installed on the exterior of the engine exhaust hose AFTER the water injection point with a pyrometer that is installed (near the turbo if there is one) and the exhaust temp is actually measured PRIOR to the water injection point? The Borel band cannot measure engine load as it is simply an overheat alarm. If the hose temp goes above the set point, the alarm goes off, meaning investigate now, there is a problem.

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and ideally save your water pump impeller

Blue Seas Systems also makes a temperature system along the lines of the Borel system. It is the M2 OLED 1841 digital temperature monitor, with temperature sensor 1821. The digital display will take up to 4 sensor and display them in a bar graph so you can see the temps as they vary, etc. You can also set the individual alarms, hi and lo for each sensor. The temp sensors are mounted with metal bands (purchased separately). I mounted these on my genset, each engine exhaust and the fourth on the wall of the engine room. Now I can see what temp each is measuring.
This year plan on mounting aqualarm flow detectors on cooling water intakes sense blockage from weeds, etc.

firehoser75 said:

Comodave,
Are you confusing the Borel exhaust hose alarm (just a band) that IS installed on the exterior of the engine exhaust hose AFTER the water injection point with a pyrometer that is installed (near the turbo if there is one) and the exhaust temp is actually measured PRIOR to the water injection point? The Borel band cannot measure engine load as it is simply an overheat alarm. If the hose temp goes above the set point, the alarm goes off, meaning investigate now, there is a problem.

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No, I don’t have them confused. An exhaust gas temperature sensor is a pyrometer. We are saying the same thing. The Borel is checking water flow by measuring the exhaust temperature after the cooling water is injected. If the cooling water stops the exhaust will immediately rise in temperature.

Good Comodave,
I must have misunderstood what you were saying. Sorry about that.

GGroves said:

Blue Seas Systems also makes a temperature system along the lines of the Borel system. It is the M2 OLED 1841 digital temperature monitor, with temperature sensor 1821. The digital display will take up to 4 sensor and display them in a bar graph so you can see the temps as they vary, etc. You can also set the individual alarms, hi and lo for each sensor. The temp sensors are mounted with metal bands (purchased separately). I mounted these on my genset, each engine exhaust and the fourth on the wall of the engine room. Now I can see what temp each is measuring.
This year plan on mounting aqualarm flow detectors on cooling water intakes sense blockage from weeds, etc.

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This looks like a great way to do it. Thanks.

djmarchand said:

Huhhh! See Wet Exhaust Temperature Alarm by Borel Manufacturing Inc..


Yes it is an external sensor that measures the temperature of the hose and alarms when it hits 165 F, and is not directly in the exhaust gas path. But you don't want that, both for corrosion and temperature stability reasons.


I will bet that more marine engines have been saved with the Borel alarm than any others including standard engine gauges.



David

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Geez, I really misread that. By “raw water” alarm, I thought they meant the upstream alarm that indicates flow, not exhaust gas temps. Thanks for setting it straight.

Remember, an alarm for all the engines. No one mentioned the generator

Nothing against the Borel unit—now that I’ve finally read about it—but it’s apparently factory-set at 165 degrees F and not customizable. I’m thinking that seeing temp trends and being able to set alarm trigger points would be preferable. I’m going to give Blue Seas a hard look.

Our boat came from the factory with an audio alarm that sounds when the antifreeze mixture in the engine reaches 205 degrees. Worked fine the time the raw water pump kept throwing the belt (pulley incorrectly positioned on the pump shaft by the rebuilder...not me). Better be quick to shut it down, though....true for any of these alarms Happened at 2 AM on a rough crossing of Lake Michigan. I was alone, so set the autopilot on a heading for Sturgeon Bay, pushed up the power on the other engine, and went below to replace the pump with the spare. Popped up every 15-20 minutes to scan for ore carrying Lakers in the sea lanes between the mines in the north and the steel mills in Indiana. I'm a proponent of overtemp warning systems, autopilots, radar, and twins.

Thanks all for the great info!! This clears up my confusion. Sammy

I did not say that I put one on my genset, but of course I did put an exhaust temperature alarm on it.

I like the Blue Seas sensors. I am going to add / build a warning system with a fire bell in the flybridge bulkhead inclosure. One sensor for engine exhaust temp, one for generator exhaust temp, and a float for high water in bilge.