lehman 120 what this wire for?

[Mostar16]

I noticed a wire out of place yesterday - from something on the water/exhaust exit elbow. See attached image. The loose end is attached to a bolt in the motor in another place.

What is this doohicky held on with a modified hose clamp the wire has pulled out of?


Yeah, it's not very clean down here. PO never paid much attention to this part of the boat.

 

[Nick F]

You have a temperature alarm on the exhaust elbow. There is a small temperature switch clamped against the elbow by hose clips with two wires connected to it.

It is a good early warning safety feature - exhaust gas temperature (after the raw water inlet to the exhaust) will rise much quicker than the engine temperature in case of a raw water circulation failure.

This is an add-on (not an original Lehman feature).

 

[Mostar16]

Thanks! That's what I suspected. Heat it up too much and it grounds the connection, meaning the other side has 12v when engine is running?

 

[tiltrider1]

It’s a nice add on if it sets off your oil/water temp alarm. I added the same switch to my Uniflite exhaust back in the 90’s.

 

[Comodave]

I have put Borel exhaust alarms on our last couple of boats. It will alarm much faster than the original equipment alarms if you loose an impeller or clog a strainer. It has a zip tie sensor that you put on the exhaust hose.

 

[Mostar16]

Thanks everyone.

It looks like the wiring is all there and all I need is a new sensor then.

 

[Nick F]

Thanks everyone.

It looks like the wiring is all there and all I need is a new sensor then.

Why do you need a new sensor?

 

[heysteve]

I'm curious about the placement on the elbow itself and wonder if this is still something that is available and recommended. The Borel and Aqualarm sensors both install on the rubber hose. At some level this makes sense as I would think the rubber hose temperature would increase much faster than the metal exhaust elbow and thus sound the alarm sooner. But seeing that your exhaust hose is not smooth, I'm wondering if the PO simply installed it on the elbow for better sensor contact.

 

[Pete Meisinger]

Could it be a grounding wire?

pete

 

[C lectric]

Those switches are Airpax/Sensata. Tony Athens strongly suggest them for exactly this use. They are N.O. and if the temp rises beyond the chosen switch temp it will close and set off any alarm and/or light you have wired to it.


It appears to me that an electrical connection has been broken off. THere should be two of those tabs for both wires to attach to.

 

[Nick F]

It appears to me that an electrical connection has been broken off. THere should be two of those tabs for both wires to attach to.

Clark - you are absolutely right. I had not noticed the lower tab broken loose from the sensor switch.

As regards the choice of mounting the switch on the metal elbow or on the rubber hose, I have always had the same doubt as to which is better. My gut feel tells me that the outer surface of the metal of the elbow would increase in temperature faster than the hose because iron is a better conductor of heat than rubber. On the other hand, there might be better thermal contact between the switch and the rubber because the rubber surface will conform.

When I have new elbows made I am thinking of having small flat areas incorporated on them for mounting the temperature sensors with better thermal contact.

 

[Mostar16]

Why do you need a new sensor?

It looks a little bit broken. The lower wire is just hanging there, but the picture does make it look like it is inserted in behind.

maurice

 

[mahal]

It looks a little bit broken. The lower wire is just hanging there, but the picture does make it look like it is inserted in behind.

maurice

If you haven’t done so already, do a test by touching the two tires together to know how the system alerts you. As mentioned above, there should be an alarm and/or light. Of course, this doesn’t test the sensor’s condition - for that, I think I would use a heat gun, but I haven’t tried.

If you have a second engine or a generator, it’s possible that the P.O. also added those sensors there.

 

[C lectric]

Since you are going with a new elbow mount the switch on the elbow, not the hose.

Tony Athens has used these things for years and he emphasizes on the metal for the higher heat transfer rate.

 

[Steve DAntonio]

This will work faster if it is clamped to the hose, but I'm not sure I'd trust it by the looks of it. I too recommend installing a Borel.

Some details here https://stevedmarineconsulting.com/onboard-alarms-part-i/