Installing temp switch on exhaust elbow

[ruvane]

I'm thinking of attaching an over temp switch to the exhaust elbow on my Volvo MD11C (raw water cooled) just where the water enters the exhaust. I reckon that this is the place that in the event of a lack of cooling water will get hottest the quickest first, so I could detect it here best.

Two questions:
- Is this the best place?
- What tempreature switch should I use?

Any other thoughts?

Yes, I know that a flow switch would react quicker, but that will come at a later stage for various reasons.

TIA

 

[Amulet]

I'm too lazy to type in how I did it again, but see this thread. To work out the correct temperature I used a thermometer like this to measure the temperature of the exhaust when running normally. (Sometimes Maplin URL's don't work - the product ref is "N92FX".)

 

[Salty John]

This is a link to our cooling water alarm product, you might be able to glean some useful information:

http://www.saltyjohn.co.uk/sentry_cooling_water_alarm.htm

Warning - commercial content!

 

[nigelmercier]

Is this the best place?
What tempreature switch should I use?

Yes.
Something like this.
Use a cable tie and thermal grease to fix it, or make some thermal epoxy with resin and aluminum* powder.

*Note spelling is as specified by Humphry Davy when he identified it, see here

 

[maxi]

Yes, you are proposing the best place for your switch and whilst the switch that nigelmercier suggests is almost right, I would opt for the version that has an operating temperature of approx 38 degrees - which means that you will get your warning very much earlier than with the 90 degree version, hence better able to reduce chances of damage.

I use just this type of switch, held in place by two narrow jubilee clips, and connected to a car horn located inside the engine box.

For the very frugally minded, the thermal switch that can be found at the bottom of pretty much every car radiator in the scrapyard will do the exact same job, and can be held into place with 'Plastic Metal'.

Using a low temperature switch "can" have a very slight downside in that; if turning on the ignition again shortly after running the engine, there is a possibility that your alarm can operate for a couple of seconds, due to the fact that the exhaust outlet will have warmed -up during the idle period, but will very soon cool again.

 

[ruvane]

Great info, thanks to all.

Not sure that 38C is not too low. The temp of the water here in summer often gets to 30C. Might go for a 50 or 60 switch.

Cheers.

 

[Martin_J]

FWIW I installed the Vetus sensor that monitors the temperature within the hose.
http://www.asap-supplies.com/marine/exhaust-temperature-alarms1/sensor-xhsh-exhaustalarmhose-mount

Installing anything outside you are then relying on the temperature of the outside of the elbow (quite a thick lump of metal) increasing in temperature. The Vetus temp sensor is actually installed (I seem to remember) at least 6" from the elbow...

I am trying to remember the other reasons for not installing a surface mounted sensor.. Seem to think that if I was installing anything then it might as well be the one solution I was most happy with.

I also seem to remember that it closes (in terms of sensor resistance) at 90C and that the exhaust gases will reach 600C rather quickly in the absence of water.

 

[SimonJ]

Temeorature alarms

I'm thinking of attaching an over temp switch to the exhaust elbow on my Volvo MD11C (raw water cooled) just where the water enters the exhaust. I reckon that this is the place that in the event of a lack of cooling water will get hottest the quickest first, so I could detect it here best.

Two questions:
- Is this the best place?
- What tempreature switch should I use?

Any other thoughts?

Yes, I know that a flow switch would react quicker, but that will come at a later stage for various reasons.

TIA

May I suggest you look at the flow switch solution once more.

Your exhaust bend will overheat when the water flow is restricted or cut off. Accordingly the best way (I think) is to discover the problem before the engine starts to overheat. That is detect when flow IN is reduced.

About 5-6 years ago PBO had a good article on fitting a flow switch between the raw water inlet and the water pump. The flow switch was supplied by CPC. The circuit was very simple.

I made up a kit (cheap and simple) since which time it has worked for 1000's of hours during extended motoring (ICW in USA, Canadian Lakes etc) - it has had a good trial! It has also saved me many times: when I have forgotten to open inlet valve (!), weed blockage, impellor failure etc. All these things without having risk of engine damage. Fitting a temperature to your exhaust will tell you of a problem TOO LATE!

Unfortunately I do have the article at hand but it must be available in PBO archives - definitely worth paying for - a cheap simple and effective proven solution that works!

 

[rogerthebodger]

FWIW I installed the Vetus sensor that monitors the temperature within the hose.
http://www.asap-supplies.com/marine/exhaust-temperature-alarms1/sensor-xhsh-exhaustalarmhose-mount

Installing anything outside you are then relying on the temperature of the outside of the elbow (quite a thick lump of metal) increasing in temperature. The Vetus temp sensor is actually installed (I seem to remember) at least 6" from the elbow...

I am trying to remember the other reasons for not installing a surface mounted sensor.. Seem to think that if I was installing anything then it might as well be the one solution I was most happy with.

I also seem to remember that it closes (in terms of sensor resistance) at 90C and that the exhaust gases will reach 600C rather quickly in the absence of water.

I am fitting an exhaust temperature switch using the honeywell switch from RS. ,same as others have posted, I measures the temperature after normal engine running at the point i wished to fit the switch on the exhaust elbow and purchased a switch with an closing temperature a little higher that the measured temperature.

I already have a flow switch in my sea water engine feed.

 

[nedmin]

I,ve fitted a thermal switch on last 2 boats. I use a switch that closes at 100 deg.C.I can assure you that if you lose water supply the temp.will get to 100deg in a few seconds.As you often get hotspots on the exhaust elbow.fasten on with a bit of wire first and if its OK in that position Araldite it. The problem with flow switches only is that you can have a burst hose and its possible not to operate.The thermal switch wont save your impeller but it wil save your engine.