Exhaust Temperature Alarm

[mikekomm1]

I'm about to install an exhaust temperature alarm on my Carver with twin Caterpillar 3208's. There are two popular products that I'm considering from Borel Mfg. and Aqualarm. Both products use a band that clamps around the exhaust after the mixer. The Borel alarm trips at 165F and the Aqualarm trips at 200F, both of these cannot be correct for the application. If 165F is the correct temp for this application, then Aqualarms product at 200F will not trip early enough and engine damage may already be taking place. If the 200F setting on the Aqualarm product is the proper setting, the Borel 165F product will set off early false alarms. Can anyone shed some light on this?

[km1125]

The exhaust alarms are for your exhaust, not your engine. They might give you some pre-warning hat your raw water is lacking flow, which will also cause engine temperatures to increase, but they don't monitor engine temps - especially if it's not a raw water cooled system.

Don't you have temperature alarms on the engine? (or should you?)

[g36]

I dont know what your temps are suppose to be but on my boat I used 2 nmea temp sensors and banded them to my exhaust and can watch temp in real time and alarm setpoint on my Lowrance electronics. Other manufacturers have nmea sensors etc. Could be more useful to do something like that if you have any modern electronics with nmea capability.

[bud37]

Welcome to the forum.........I think I might check the exhaust hose temps with an IR gun before I decided........also have a look at the temp spec on your hoses......the best defense imo would be the 167F......even if it was a bit of a false alarm you would not be near the point of losing the hoses......remember the install point is right where the water is injected to the hose, that part of the hose will show issues quite quickly.
I do agree that the two specs are confusing unless there is some explanation in their install manual...

[tomschauer]

I may be mistaken, but I believe the temperature in the engine compartment would be higher than the wet exhaust temperature. If you have an externally mounted sensor, I would bet you are reading the engine room temp in the summer and not the exhaust temp?????????????

[bud37]

As I see it....with the engines off and ambient at lets say 100F then all would be that temp give or take, but as soon as the engines run then the wet hose would be cooled by the raw water inside....the sensor reads the temp of the hose at the injection point........actually if you shoot wet hoses up and down you will see quite a variance in temps due to the swirling effect in the hose itself..... I believe that is the reason why it is important to put the sensor in the exact right spot. You really aren't reading the exhaust temp just the hose surface.

[Viper]

You really need to confirm what the temperature spec is for the hose you have as a starting point. Many have a top end of 200*F, some 250*F, some 350*F, etc. You want to ensure the sensor you install will trigger a warning before the hose reaches its upper operational limit with a safety margin. Having said that, you don't want it triggering so high that it takes longer to alert you to a problem than the engine temp alarm does, so you're looking for a happy medium. As mentioned above, knowing what the normal actual measured temps are during a good run will help you make an educated decision on which limit to go with. The whole idea is for you to be alerted early through higher than normal exhaust temps before your engine temp climbs too high. When cooling water volume drops to a certain threshold, it won't take long for exhaust temps to rise. This could happen before your engine actually realizes a rise in temps.

[tomschauer]

I guess again, I wasn't clear on my thoughts.

I was thinking with a 90 degree f outdoor temp, and two engines at cruising speed, I would think it could easily hit 165 f in the engine room. Unless your exhaust temp sensor is immersed in the exhaust flow, you could read an alarm when actually nothing is wrong.

On the other side of the coin, with a higher temp alarm, again on the outside of the hose (remember the hose has some insulating qualities) I would strongly believe your motors would show overheat long before the sensor shows an alarm.

I guess I am saying, if the sensor isn't immersed in the exhaust flow, the information it provides has minimal value at best. IMHO.

[PhilH]

Tom...I dont think with the amount of air entering running engines the room will get that hot. The best probes are ones that tap into the exhaust water which should not go over 200 degrees or so. I am also trying to figure out where to put temp probes on my Cat 3208TA's. The band sensor will only work well if it is in contact with metal, and around 200 degrees or above is where you start to have trouble. Just my opinion. Willing to hear your ideas.

[g36]

It's interesting to me no one seems to think a real time exhaust temp reading is valuable to have except me. Knowing what normal is and when it starts climbing I know ahead of time somethings not right.