Exhaust temperature

chubby

chubby

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hampshire, uk
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Having been saved by sea start from meltdown over a cooling water failure when the panel lights didn't` give me enough warning, I have fitted one of the NASA exhaust temperature monitors: very easy to do and works fine, recommended!

Now the question of the temperature ( heavy long keel 33 foot with vetus 42 HP 4.17) At 1800 RPM I get 5 knots and the monitor reads 30C, 2000 RPM gives 6 knots and about 33C, full power at 2500 gives 6.5 knots and 40C, in flat calm and no sea running.

The factory default is 85C but they suggest 10C above the full power reading so I changed mine to 60C to allow for the engine working harder in worse conditions, what do thers do?
 
I've just fitted something similar this season. Early days yet (and I'm only on a lake anyway) but I haven't seen it go over 30 degrees just at the exhaust elbow, even with the mighty 12HP donkey at full chat.
 
Just had a quick look at this, how secure is the connection the sensor makes with the exhaust when installed? drilling into the exhaust would make me nervous!
I do need something like this though, having suffered a major overheat I'm paranoid about a reocurrance.
 
I have a brass plug screwed into a tapped boss in the exhaust elbow. No idea what it was there fore in the first place. I drilled a blind hole almost all the way through it and then epoxied the thermocouple into the hole. The absolute temperature it records isn't important. I just set the alarm for something higher than it will ever be in normal running (currently at 50 degrees C). If the boss hadn't been there, I might have been tempted to just trap the wires under the hose with the thermocouple in the gas flow and tighten the hose clip. They're so thin, I doubt it would ever leak.
 
I looked at the NASA exhaust alarm, but their website says the EX-1 (latest model?) is not waterproof and must be mounted somewhere dry. I'm not sure how to get around that on my boat.
 
The sensor is a tight fit in the 5mm hole drilled in the exhaust hose and held in with two hefty cable ties designed to take the temperature, seems OK to me and easy to fit, I too was paranoid after a major overheat but luckily in Portsmouth harbour on a quiet day when I was able to sail onto a buoy and let things settle then sort myself out but if in mid channel could have been a nuisance. The EX1 is not water proof but there is plenty of cable to let you put it near a chart table, mine is in a cubby hole in the wheelhouse.
Murv said:
Just had a quick look at this, how secure is the connection the sensor makes with the exhaust when installed? drilling into the exhaust would make me nervous!
I do need something like this though, having suffered a major overheat I'm paranoid about a reocurrance.
Click to expand...
 
chubby said:
The sensor is a tight fit in the 5mm hole drilled in the exhaust hose and held in with two hefty cable ties designed to take the temperature, seems OK to me and easy to fit, I too was paranoid after a major overheat but luckily in Portsmouth harbour on a quiet day when I was able to sail onto a buoy and let things settle then sort myself out but if in mid channel could have been a nuisance. The EX1 is not water proof but there is plenty of cable to let you put it near a chart table, mine is in a cubby hole in the wheelhouse.
Click to expand...

Sounds ideal, thanks for the reply :)
 
My temp probes are surface mounted in small copper tubes filled with heat conducting paste. The tube is bedded to the metal surface in epoxy putty, which also conducts heat well. We routinely do this on both hot and cold pipes on large fridge systems, and expect rapid and accurate (0.1deg C) measurements between -40 to +150C. The first thing that will get hot if the cooling water fails is the injection bend.

Detecting a problem on this at around 50C means the rest of the system will not be that much higher, and shouldn't have reached danger point yet.

So I personally would avoid drilling holes into the pipes.
 
Avocet said:
I have a brass plug screwed into a tapped boss in the exhaust elbow. No idea what it was there fore in the first place. I drilled a blind hole almost all the way through it and then epoxied the thermocouple into the hole. The absolute temperature it records isn't important. I just set the alarm for something higher than it will ever be in normal running (currently at 50 degrees C). If the boss hadn't been there, I might have been tempted to just trap the wires under the hose with the thermocouple in the gas flow and tighten the hose clip. They're so thin, I doubt it would ever leak.
Click to expand...


That would be for a tempprobe to be fitted

Worst thing you sould do as you have now weaked your exhaust pipework thus causing a weak point where it will be the first place to blow.
 
Last edited:
When you say "blow"... this is a 12hp raw water cooled engine! Exhaust back pressure is barely above atmospheric. Brass plug is 25 years old with no sign of deterioration on the end facing into the exhaust as yet. I've got a few mm of brass to corrode through before the exhaust gas comes into contact with the end of the thermocouple and the epoxy. Even after that happens, I'd only expect a slight weep from the hole in the plug rather than some sort of catastrophic failure. When (if) that happens, I might have to knock up another brass plug, I guess, but I'd expect this engine to be well and truly dead by the time that happens. (It's on borrowed time right now, to be honest)! Frankly, I'd be much more worried about drilling a hole in the rubber exhaust hose, poking a thermocouple through it and holding it in with a couple of big cable ties!
 
Avocet said:
When you say "blow"... this is a 12hp raw water cooled engine! Exhaust back pressure is barely above atmospheric. Brass plug is 25 years old with no sign of deterioration on the end facing into the exhaust as yet. I've got a few mm of brass to corrode through before the exhaust gas comes into contact with the end of the thermocouple and the epoxy. Even after that happens, I'd only expect a slight weep from the hole in the plug rather than some sort of catastrophic failure. When (if) that happens, I might have to knock up another brass plug, I guess, but I'd expect this engine to be well and truly dead by the time that happens. (It's on borrowed time right now, to be honest)! Frankly, I'd be much more worried about drilling a hole in the rubber exhaust hose, poking a thermocouple through it and holding it in with a couple of big cable ties!
Click to expand...

I wasn't refering to the brass plug, I was refering to the fact you have drilled the exhaust pipe thus weaking/thinning the diameter of the exhaust pipe therefore causing a point of weakness.
 
superheat6k said:
My temp probes are surface mounted in small copper tubes filled with heat conducting paste. The tube is bedded to the metal surface in epoxy putty, which also conducts heat well. We routinely do this on both hot and cold pipes on large fridge systems, and expect rapid and accurate (0.1deg C) measurements between -40 to +150C. The first thing that will get hot if the cooling water fails is the injection bend.

Detecting a problem on this at around 50C means the rest of the system will not be that much higher, and shouldn't have reached danger point yet.

So I personally would avoid drilling holes into the pipes.
Click to expand...

Now that sounds a very good idea.

Is it the same sort of heat conducting compound applied to computer CPU chips?
 
Murv said:
Now that sounds a very good idea.

Is it the same sort of heat conducting compound applied to computer CPU chips?
Click to expand...

I agree, that sounds a neat idea. Are the copper tubes/sensors etc bought as a unit, if so where did you buy...or is it something you've made up yourself in which case can you share the details. Thanks
 
PITCAIRN said:
I agree, that sounds a neat idea. Are the copper tubes/sensors etc bought as a unit, if so where did you buy...or is it something you've made up yourself in which case can you share the details. Thanks
Click to expand...

We buy them from our US Controls supplier, as a sealed end tube about 2" long and the come filled with the paste, but a small piece of copper tube just bigger ID then the probe will suffice,, e.g about 1/4"

If you want the tubes we use please PM me, but they are about £8 each, which is why a short length of 1/4" with one end crimped hard with mole grips will suffice. Castrol LM grease will work as well for the heat conducting medium, as I am not sure where to buy proper heat paste.
 
superheat6k said:
We buy them from our US Controls supplier, as a sealed end tube about 2" long and the come filled with the paste, but a small piece of copper tube just bigger ID then the probe will suffice,, e.g about 1/4"

If you want the tubes we use please PM me, but they are about £8 each, which is why a short length of 1/4" with one end crimped hard with mole grips will suffice. Castrol LM grease will work as well for the heat conducting medium, as I am not sure where to buy proper heat paste.
Click to expand...

Superb, thanks very much.
 
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