Can you extend the lead on a thermometer?

Murv

Murv

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I need a cheap, quick way to monitor the engine temperatures from the flybridge, the engine temperature readouts are only fitted on the saloon helm for some odd reason.

I have a few cheapy thermometers with remote probes, but I estimate that the wires would need to be extended to the best part of 30' to reach from FB to the engines.
From there, the plan is to cable tie, or tape, the probes to the outside of the exhausts, after the water elbow.

1) Would this work?

2) Would it give me any meaningful warning of overheating problems before damage occurs?

I must stress that this will be a temporary measure and I'll get something a bit more robust installed in due course. But, we have a fairly lengthy trip coming up very soon and I'm fairly unhappy about the prospect of travelling any distance with no indication of engine temperatures, other than keep nipping downstairs to check.
Obviously, I could just helm form the saloon, but as aft visibility is non existent, and (hopefully) the weather might be nice enough to be out side, it would be nice to have the option of staying on the flybridge.
 
gordmac said:
Are you talking about a thermocouple? Kong time since I had to know much about them but from memory it isn't straightforward.
This may help
http://uk.rs-online.com/web/general...e-in-extending-thermocouple-cable&id=infozone
Click to expand...

Thanks for that, I guess it is a thermocouple then, it's this type of thing:

IMAG0316_zpshwqkjobq.jpg


It's not looking as if adding 30' of speaker wire is going to cut it then! thanks for the link, back to the drawing board!
 
Simple solution for the short term is a car dash camera looking at the gauges running to its screen up in the flybridge, £30 solution if you can get a separate camera and screen but many have a video out function. Also useful for visual monitoring of the engine room and bacon in the grill.
 
Colvic Watson said:
Simple solution for the short term is a car dash camera looking at the gauges running to its screen up in the flybridge, £30 solution if you can get a separate camera and screen but many have a video out function. Also useful for visual monitoring of the engine room and bacon in the grill.
Click to expand...

Thanks for that, I was thinking along those lines as a backup plan.
I've got a gopro copy thing that connects wirelessly to my phone, so wouldn't cost anything to set up.
And, the option of monitoring the grill has swung it for me :D
 
There are all sorts of thermocouple and each require there own compensating cable to reduce cold junction errors. You need to find the type of TC you have and then buy the correct compensating cable. FYI , compensating cable usualy have two different wires, one to suit each keg of the TC. However, your sensor may be a thermistir type which (I think) uses standard copper cable.
 
Jcorstorphine said:
There are all sorts of thermocouple and each require there own compensating cable to reduce cold junction errors. You need to find the type of TC you have and then buy the correct compensating cable. FYI , compensating cable usualy have two different wires, one to suit each keg of the TC. However, your sensor may be a thermistir type which (I think) uses standard copper cable.
Click to expand...

Thanks for that. To be honest I have absolutely no idea. They were literally pennies each, they run on watch batteries and bought from Hong Kong as I thought they might be useful for something.

I guess, then, the simplest way is just to try it and compare it alongside? Very little lost if it doesn't work, and even if the temperature readout is off, as long as it's relative, it wouldn't actually matter?
 
Murv said:
Thanks for that, I guess it is a thermocouple then, it's this type of thing:

IMAG0316_zpshwqkjobq.jpg


It's not looking as if adding 30' of speaker wire is going to cut it then! thanks for the link, back to the drawing board!
Click to expand...

I doubt that it is a thermocouple type it's most likely a temperature variable resistor.

I have a similar type in in fridge and freezer that I have extended the cable on but not quite as long as you have.

Cut the wire then rejoin temporary and take known measurement then extend the wire to the length you wish on the bench and check the temperature again under the same conditions. If they match all OK.
 
Rogershaw said:
I doubt that it is a thermocouple type it's most likely a temperature variable resistor.

I have a similar type in in fridge and freezer that I have extended the cable on but not quite as long as you have.

Cut the wire then rejoin temporary and take known measurement then extend the wire to the length you wish on the bench and check the temperature again under the same conditions. If they match all OK.
Click to expand...

Sounds like the simplest plan :) Thanks for that, I shall give it a try this evening
 
What temp are you expecting?

Does the fridge thermometer go high enough?

Your ideal would be a 1-wire solution - OTTOMH 100m limit.
Would probably mean following a how to on the internet...
 
What type of readout do you have at the lower helm? It may be easier to set up a repeater display to the flybridge if rogershaw's solution doesn't work.
 
Some simple thermometers also measure the forward volt drop of a silicon diode. (you know the .7v we always talk about) that actually varies with temp. So yes just extend the wires if it is diode or NTC resistor type. Thermo couple type is very unlikely being a bit more sophisticated and more suitable for high temperatures.
Just waffling small petrol piston engined aircraft often have a Cylinder Temp Gauge which can be used to adjust fuel air mixture. (desirable at altitude). They are a thermocouple type where 2 washers of the 2 different metals are pressed together to make a spark plug washer. (with 2 wires coming out) I always thought they would be excellent for any piston engine in some form indicating actual metal temp of the cylinder head so early indication of any problem. (outboard engine?)
Mostly we measure coolant water temperature which is OK unless we lose all coolant which may then not indicate cyl head temp. (just waffling) olewill
 
Thanks all :)

Grumpy, the lower helm is a simple analogue temperature gauge. From a related question I asked on the mobo forum (for a long term solution) the idea of repeaters was suggested and is viable.
For now, the extended wires is a free, quick fix that will do the job :)

Shiny, it's not actually a fridge thermometer, that was just one I had laying around at work to show to type of thermometer I meant. Although, in the lab we've actually calibrated these at up to 70degC with < +/- 0.1degC accuracy at 70DegC so would be fine for the exhaust (after water injection)

William, that is a bit of a concern of mine, that a total coolant loss wouldn't be shown.
I guess though, in reality, unless something cracks very violently, or a hose detaches completely, then coolant temperature would rise rapidly before failing to reach the sender.

Thanks for all of the valuable input, as ever :)
 
A probe attached to the rubber hose just after the water injection point would give a near instant and big rise in temperature if coolant was blocked - all you'd have would be hot exhaust gasses!
 
William_H said:
Mostly we measure coolant water temperature which is OK unless we lose all coolant which may then not indicate cyl head temp. (just waffling) olewill
Click to expand...

One of my cars (the same type as you have) had a level indicator in the coo;ant tank and I was thinking of fitting a stainless steel float switch into the header tank for the same reason.
 
Colvic Watson said:
A probe attached to the rubber hose just after the water injection point would give a near instant and big rise in temperature if coolant was blocked - all you'd have would be hot exhaust gasses!
Click to expand...

That's the idea, I guess it's the most likely failure.
But, if the closed circuit failed, would there be any sort of rise of rise in EGT that would show up? I suppose it's a small risk, far lower than sucking a plastic bag into the raw water intake, anyway!
 
Quick update, as above, it works fine.
Extended the wires on 1 thermometer, and left 3 as controls.
Ambient temperatures were all showing similar, then dropped the probes into a cup of water at around 70degC
The temperature variation across all 4 thermometers was well under 1 deg C, with the worst culprit being one of the uncut ones.
I didn't go as far as plotting RSD values across a range of temperatures ;) but suffice to say they will serve my needs of giving warning of temperature changes on the exhausts.
 
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