Ac2w temp switch

[cmarley79@hotmail.co.uk]

Hi, I have a sensor on the lower side of my Ac2w that I think might be a temperature sensor. It's got three terminals and if I try to take it off the oil comes out. Can someone tell me what this is and if it's a temp sensor how to wire it up ?
Thanks chris

[listard-jp2]

It is more likely to be an oil pressure switch, than an oil temperature sensor.

If it is an oil switch it will have contacts which make and break depending upon oil pressure. If it is a temperature sensor then the resistance across these terminals will change as oil temperature increases.

[cmarley79@hotmail.co.uk]

There's something that looks exactly the same on eBay and it's described as a temp switch. As the engine is air cooled I'd like to have some indication of temperature. It's going in a 30 foot sail boat to hopefully bring it through the Caledonian canal so it's got a bit of work to do lol 😂

[LowGear]

Where do the wires go?

[cmarley79@hotmail.co.uk]

That's what I want to know  🤔?

[dieselgman]

On the OP switch the individual machine control wiring will vary depending on whether it is using BOR "break on rise" or "make on rise" logic. There is a C common lead - usually the middle connection, then a NC normally closed and also a NO normally open contact. (A simple continuity test will identify the leads if they are not legibly marked.) Above about 10psi the switch changes position internally such that one contact opens and the other closes. So, your control circuit will use 2 of the three contacts only... A simple Make On Rise setup is often configured with a bypass timer or switch to allow the control relay to operate while you are cranking, starting at zero oil pressure, or even better sometimes, just a simple series circuit that will only open the fuel/throttle control relay after the oil pressure reaches the threshold point in the switch.

The correct answer for your situation depends on the type of control system installed with your engine. Some modern ones use digital logic and can be triggered by either type of circuit. Many of the newer Listers have a simple Make On Rise series wiring scheme.

dieselgman

[cmarley79@hotmail.co.uk]

Thanks that's really helpful, I'll check it with the tester today. If it is an oil pressure switch then I'm still left with the same problem of not having a temp sensor tho 😳

[AdeV]

...If it is an oil pressure switch then I'm still left with the same problem of not having a temp sensor tho 😳

How handy are you around a soldering iron? It wouldn't take long to throw together a temp sensor hooked up to an Arduino, with a display that can be routed to the cabin, and even an alarm if it goes too high (or a shut-off mechanism).

I'm not sure measuring the oil temperature will give you enough time to react to an overheat situation, you may be better monitoring the head directly, or even the ambient air coming out of the fan exhaust. I'll be honest though, I don't have much experience of air-cooled engines, and water cooled ones like the Lister have the advantage that if they go north of 100 degrees C, you KNOW they need shutting down ASAP!

[dieselgman]

AC2W will be water-cooled and should have a water temp sensor installed somewhere in the cylinder head area. Oil temps are a non-issue on these machines.

dieselgman

[cmarley79@hotmail.co.uk]

Ok so I've made progress, it does seem to be an oil pressure switch. As soon as the engine is running it switches over to the other terminal. I've taken the cover off the top to inspect the cylinder head but I didn't see any sensor there. I have found a tiny 2 terminal ( micro therm ) sensor that is screwed to the bottom side of the block, it's broken but I'm sure I'll get something similar. It seems like an odd place to put a temp sensor to me but has anyone else came across anything like this?

[cmarley79@hotmail.co.uk]

P.s it is air cooled 👍

[dieselgman]

Thanks for that correction... 

Lister used a BOR (break on rise) cylinder head temp switch on some of their air-cooled engines of that vintage. The head temp switch would be used in series with the oil pressure switch to control a shut-down solenoid on the fuel rack. However, AC2W may not be using the same hardware. I will have to take a look at the parts books to see what accessories might have been installed.

dieselgman