Engine Temp Sender - M18

[mherrcat]

The temp sender on my Universal M18 may be dead. I tested the function of the temperature gauge and it appears to be OK. I used a multimeter to test the sender itself and the resistance readings do change as the temperature goes up, but no reading on the gauge.

Torresen Marine sells a replacement sender unit for about $45. I was wondering if this is a reasonable price or if there are other sender units available for less that will work as well.

Before I buy a new sender I want to test the existing sender again just to be sure. Any tips on what resistance readings I should be getting on the sender when I test it with the multimeter?

 

[Maine Sail]

In my experince..

In my experience, four out of five times, it's been the gauge and not the sender. The replacement gauge is nothing more than a Teleflex Red International series and they sell for about $20.00 give or take.

I have had gauges test fine but that were still bad...?? How did you test the gauge? Hamilton, Defender & West all sell the Teleflex gauges. You do not need to buy it from Universal/Westerbeke and grab your ankles...

 

[mherrcat]

Thanks. I will check out those sources.

I tested the gauge according to a procedure in Nigel Calder's book on marine diesel engines. There were several steps to the test, involving disconnecting and/or grounding the terminals on the gauge that connect to the power switch and to the sender and noting whether the gauge needle moves to its lowest or highest position.

I didn't want to deal with the rats nest of wiring behind the engine control panel to test every leg of the circuit so I just disconnected the wire at the sender and either left it ungrounded or grounded and turned the engine switch on. I figured this would test the complete circuit and if the gauge didn't respond I would start looking at individual legs of the circuit.

The gauge needle moved to it's lowest position in one test and to it's highest in the other, as the book noted it should. (Without the book in front of me I don't remember which way it is supposed to move when grounded and when ungrounded, but it passed the tests.) I figured this indicated that the gauge was getting power, the circuit was good all the way to the sender and the gauge was functioning.

I used a multimeter to measure the resistance of the sender unit when cold and when the engine had warmed up. This is where I'm not certain about my method, because I had the meter set to the wrong scale when I tested the cold sender. But after I realized my mistake I tested the sender twice as the engine got up to temp and the reading was going lower by several ohms; not much but a little.

If the gauge is OK, are there other sources for the sending unit, or do I have to get that from Universal/Westerbeke?

 

[Tom Metzger]

Go to the source

Here is the Teleflex guide for temperature gauges:

http://www.downloadingfiles.co.uk/teleflexfiles/gauges/Inboards, I-O's.pdf

These are automotive parts rather than marine, so the best place to get senders is at an auto parts store. It is best to take the old one with you to make sure you get the right configuration, but really the only major concern is the thread.

The senders are generic, so don't worry about the brand.

 

[mherrcat]

Thanks!

I'll probably try to re-test the sender this weekend and replace it.

 

[mherrcat]

While re-testing the sender and gauge it occurred to me that the sender is just a type of variable resistor; a potentiometer if you will. So I ran up to Radio Shack and bought a 1K Ohm trim pot and some alligator clips to make a couple of jumper wires.

Measured the resistance of the sender cold and got about 1100 Ohms. Ran the engine for 30 minutes and measured about 221 Ohms. This wasn't low enough to move the gauge needle.

Using the multimeter I then set the trim pot to 100 Ohms and temporarily wired it into the circuit bypassing the sender. The temperature gauge registered about 160 degrees. Set the trim pot to 50 Ohms and the gauge registered about 180 degress.

So I think I pretty much confirmed that the gauge is OK and the sender is bad. I ordered a new one from Featherman Enterprises - very nice to deal with and helpful on the phone by the way.