Exhaust Temp Sensor vs Raw Water Temp Sensor

[Comodave]

I am a big fan of Blue Seas equipment. I have not looked at their system. The Borel system allowed me to have 3 exhaust temperature alarms, 2 water in fuel alarms for my Racors and 2 high water alarms custom made for my application. It has a built in horn that is very loud and would be heard over the engine noise. Also it only draws power when it is alarming.

 

[firehoser75]

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

Sorry Dan, but I did back in Post #9. It was a while back in a longer post, so I can understand how you forgot.

 

[Seevee]

Seems like measuring the exhaust temp after mixing with the exhaust water is just a water temp gauge. I'd argue that a water flow indicator in the same spot would be MUCH more valuable, giving you an indication of trouble before the engine gets hot.

And a second vote would be for an antifreeze temp gauge which would give an indication if the belt broke and the freshwater pump stopped. The exhaust water flow won't show that with the flow gauge and will show it later with a temp gauge.

Thoughts?

Now shopping

 

[Comodave]

I would not want a water flow sensor in the exhaust stream. It will be an ongoing maintenance problem with the corrosive exhaust gases. The exterior temp sensor is a water flow sensor in effect.

 

[firehoser75]

Seevee,
I agree completely with Comodave!
When my exhaust hose overheat alarm was going off (due to a problem) in the summer of 2017(explained in an earlier post in this thread), my mixing elbow was providing the necessary AMOUNT of cooling water. However, it was not providing the correct PATTERN of cooling water, hence the hotspot detected by the exhaust temp alarm. Every other spot on the engine, heat exchanger, turbo, engine block, even other spots on the hose, etc. etc. were reading very good temperatures (185 or lower), but there were 2 spots on the exhaust hose that got up as high as 225 degrees. The hose was rated at 200 degrees F continuous and 250 intermittent. A water flow alarm would not have caught this common problem (a corroded exhaust elbow) nor would the "normal" coolant temperature alarm!
In my case, due to the installation and design of the OEM exhaust elbow, if this problem had not been caught in time, I could have had saltwater enter my turbo and/or the exhaust side of the engine potentially causing major damage (worse case new engine). In my opinion, this alarm SAVED MY BACON. For $75 this alarm is cheap insurance, but each to his own.
To me, the raw water flow alarm (which I also have and like) that is installed near the seacock, is really there to help me get to the seacock if I left it closed to avoid impeller replacement and to warn if there is another problem (such as blocked inlet).

 

[chartervet]

Just been researching this...

Aqualarm now builds an exhaust hose monitor, nicely packaged and competitive with Borel. Go to their website for details.

Thanks for all the positive Borel comments. Equipping a new-to-my-friend GB42 with twin 3116 Cats.

Will get Borel or Aqualarm.

 

[High Wire]

The fastest response sensor to a loss of seawater flow would be the flow switch. It either senses flow or no-flow, practically instantaneous. No waiting for temps to rise. The problem is it is a moving component in salt water that can corrode and fail either way.

An exhaust temperature sensor takes time for the actual exhaust temperature to rise plus the time needed to conduct the temp rise across the hose or riser that it is attached to. Additionally there is a time response of the switch itself. Is it fast enough to stop damage? The hope is yes. It's not in contact with saltwater so its reliability is higher.
Not sure what a raw water temp alarm buys you that the engine coolant gauge and alarm does not already provide.

 

[DavidM]

Not sure what a raw water temp alarm buys you that the engine coolant gauge and alarm does not already provide.

This is what it buys you:


When you suddenly lose raw water flow due to a blockage at the inlet, shredding the impeller, or whatever, the main heat exchanger starts heating up and the exhaust through the rise starts heating. At high loads it takes less than a minute, maybe 10-20 seconds for the exhaust hose to heat up enough to trip a Borel alarm. Then when you hear the alarm you throttle back to idle and no harm is done.


If you don't have an exhaust gas alarm or similar raw water flow alarm, the exhaust hose gets real hot and starts to burn inside, maybe the muffler melts.


The coolant temp starts to rise. Often the coolant alarm won't go off for several minutes until some of the coolant has boiled off, and the head heats up enough to trigger the alarm.


In this case it is several minutes before the coolant alarm goes off, not seconds. Sometimes the head gasket blows and the head is warped. Even worse can happen.


The Borel and similar alarms buys you minutes and is worth every penny.


David

 

[Albin]

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!!

Well, I think I will get some heat for this suggestion (pun intended) but I have a cheap solution for monitoring exhaust temperature which I have been using for about 10 yrs now and it works like a charm. I actually use a barbecue meat monitor. That's right, you read it right. The one I use is made by Redi Chek (pictured below). They cost is less than $50.

I attached the probe to my engine exhaust injection elbow which is connected to a sending unit in the engine room. The receiver is mounted on my flybridge console where I get a continuous real time temperature reading. That signal is going through two decks without any problem. The beauty of this system is that it gives continuous temperature readings, not just a maximum temperature alarm, so you can see the temperature creep up long before it becomes a problem.

Some might say it does not give an accurate reading of internal temperature if it strapped to the outside of the exhaust elbow. To that I say, that doesn't really matter. The point is once you know what is normal for various engine rpm, you will then know if there is any kind of problem long before it gets too hot to cause damage. Also, it is a lot better than what most boaters have, which is nothing.

By the way, I think it is also a good idea to have a raw water flow monitor for the engine and generator.

 

[High Wire]

This is what it buys you:


When you suddenly lose raw water flow due to a blockage at the inlet, shredding the impeller, or whatever, the main heat exchanger starts heating up and the exhaust through the rise starts heating. At high loads it takes less than a minute, maybe 10-20 seconds for the exhaust hose to heat up enough to trip a Borel alarm. Then when you hear the alarm you throttle back to idle and no harm is done.


If you don't have an exhaust gas alarm or similar raw water flow alarm, the exhaust hose gets real hot and starts to burn inside, maybe the muffler melts.


The coolant temp starts to rise. Often the coolant alarm won't go off for several minutes until some of the coolant has boiled off, and the head heats up enough to trigger the alarm.


In this case it is several minutes before the coolant alarm goes off, not seconds. Sometimes the head gasket blows and the head is warped. Even worse can happen.


The Borel and similar alarms buys you minutes and is worth every penny.


David

Dave, I'm good with sea water FLOW and exhaust TEMP. Never seen Raw Water TEMP used. Where would that get installed that would do any good? On flow stoppage past the sender, the sensed temp would only creep up depending on location while engine coolant temp zooms up.

 

[OldDan1943]

Folks, no matter which system you elect to use, pick it, install it, use it and dont look back.
Each and every system will have it merits and short-comings.

Remember, people have driven boats without them for years.
For years, folks measured the remaining fuel via a stick or a sight glass or just plain looking into the tank.
Same way with engine temp. Strap a direct reading temp and inspect the engine room frequently.
On a nuc sub, shutdown watch, 1 person would need to record the temps (at least 5 pages) of direct reading thermometers.
It would take close to an hour to get all the readings in 2 compartments.
A side effect was, ensuring each compartment was still water tight, no broken or leaking pipes, no fires etc.

 

[firehoser75]

Good point OldDan!
I think it is possible that some are getting confused with "terminology". When I googled "raw water temperature alarm" I did not find anything except the previously discussed "exhaust hose temperature alarms". Other than monitoring the temperature after the raw water is injected into the exhaust gases at the mixing elbow, I do not understand how knowing the raw water temperature (anywhere else) would be very helpful.
Both Borel and Aqualarm make good products. One just alarms slightly earlier than the other. Your choice what works best for your 'peace of mind".

As far as the flow alarm goes, I can't see how it would fail in such a way that it would not be constantly alarming, therefore alerting you to a problem. However, even if it somehow did fail without alarming, if you also had an exhaust temp alarm in place, then you are still protected as described by Dave.
As far as the BBQ temp device, again each to his own. I would not want to rely on having to constantly monitor the temperature. However, with that being said, I go into the ER a few times a year and record temps from a number of locations using an IR gun. This lets me monitor trends.

 

[angus99]

The Blue Sea monitor someone pointed to earlier alarms, has programmable set points and gives digital temperature readouts for four separate sensors. You can also add an alarm for a second helm, if needed. Comes with four sensors, but you have to supply the bands to clamp them in place. I plan to install one to monitor the exhaust hoses on both our Lehmans and perhaps near the expansion tanks to serve as a backup alarm if the engine coolant overheats.

 

[DavidM]

Archie:


Sorry I didn't mean to imply a raw water temperature alarm, only exhaust temperature after the raw water injection elbow.


David

 

[BrianSmith]

Seems like measuring the exhaust temp after mixing with the exhaust water is just a water temp gauge. I'd argue that a water flow indicator in the same spot would be MUCH more valuable, giving you an indication of trouble before the engine gets hot.

And a second vote would be for an antifreeze temp gauge which would give an indication if the belt broke and the freshwater pump stopped. The exhaust water flow won't show that with the flow gauge and will show it later with a temp gauge.

Thoughts?

Now shopping

My Aqualarm raw water flow sensor is about 2 ft. from where the raw water is injected into the exhaust elbow, so yes, I agree with you, Seevee, that at that point, it will warn of practically the same thing as the exhaust gas temp alarm: insufficient flow of raw water. And it will alarm sooner in the case of a sudden loss of raw water flow (sucked up a plastic bag into the inlet, for example). But if the loss of flow is not dramatic, it may not set off the alarm, but because of the decreased flow getting into the exhaust, the exhaust gas temp would still start to rise. So, with a belt and suspenders attitude - have both!

And yes, you absolutely need a temp gauge for the antifreeze, but I can't hardly imagine a boat builder not equipping a boat with one of those, so everyone probably already has one.

 

[Group9]

and ideally save your water pump impeller

Just stopping that from happening once would be worth it!

 

[Steve DAntonio]

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!!

ABYC standards do call for a means of alerting the vessel operator in the event of a loss of cooling water for engines.

I strongly recommend the the exhaust temp sensor over the raw water flow sensor for a few reasons. The raw water flow sensors can get stuck open or closed, thereby giving you a false reading.

Most importantly, however, the raw water flow sensor, if installed before the raw water pump, as most are, will not alert you to a parted hose in the raw water cooling system after the pump. I've seen this occur on a few occasions, the hose fails between the engine and exhaust system, so the engine does not overheat, but the exhaust system does.

At cruising speed, without water, the exhaust system can be severely damaged in a matter of a few minutes, rubber hose and FRP pipe that's designed to operate at 150F is cooked very quickly when exposed to 400-1000F dry exhaust. The repair cost, assuming the vessel doesn't flood or catch fire and sink, can be eye-popping. I made a post here a few months ago about a ferry in Florida that caught fire (with the loss of one life) as a result of a loss of cooling water for the engine and exhaust. I believe if that vessel had an exhaust temp alarm the tragedy may have been avoided, although the captain did inexplicably only reduce the engine to idle speed, rather than shutting it down, when he received an indication of an engine overheat.

Scores of clients have told me how exhaust temp alarms have saved their bacon. In the event of an intake clog, the alarm typically sounds within 30 seconds, nearly always quick enough to avoid damage to the impeller if the engine is shut down as soon as the alarm sounds.

More on the system here https://stevedmarineconsulting.com/onboard-alarms-part-i/

 

[ProMaritime]

I like knot meters on power boats for other reasons but You also need to measure the raw water discharge temp. Any type knot meter (paddle wheel or high tech) usually measures sea water temp. as well as boat speed which should be the same as your raw water inlet. If you have a wet exhaust with mixing elbow the place to take that temperature is just downstream of the elbow.