3ym20 Yanmar fuel sensor

[Martin G]

Hi there,
I love renovating old boats.
I bought recently a 1971 Norwegian Myra 21 boat with a Yanmar installed. Engine is in good shape but the original tank is too small and has no fuel sensor installed. The cable harness shows a free single cable marked 'fuel'. I'm wondering what type of fuel sensor should go there. I believe the panel has only a low fuel warning, right?

Thanks for your kind support.

Martin

Never give up hope.
Foto shows my former project in New Zealand.

[Wotname]

The 'standard' 3YM20 instrument panel does not have any fuel indication or fuel alarm fitted. You may have some other Yanmar instrument panel or you may have a custom panel.

The 3YM20 wiring harness does not have any spare wiring for a fuel sensor but again, you may have some other Yanmar harness, maybe fitted in the past.

Some larger Yanmar engines have a 'water sensor' in the fuel filter and this brings up a fuel alarm on the respective instrument panel.

Could you post a picture of your instrument panel?

Attached is the standard 3YM20 panel.

[Martin G]

Hello Wotname,
attached the panel of my boat. It looks different.

Cheers

Martin

[bil56]

first pic: standard panel B20
other pic: panel C30 (not for YM)

[Martin G]

Please have a look at this document. The initial question remains! Which kind of fuel sensor belongs to this panel. Thanks!

[skipperpete]

Fuel filter water alarm! If it has a green and red wire to it, otherwise, buggered if I know.
Your project boat looks a lot like my old Harding ships workboat, does it have a 75 hp Mitsubishi diesel and a Kort steerable nozzle?

[Wotname]

While this is not a direct answer to the OP's question, it would appear the OP's panel is a Yanmar B20 panel
See https://www.yanmar.com/marine/product/panels/b20/

The next step is to track down the specs for the optional fuel level gauge. I'm guessing the fuel level shows up as the dashes under the fuel bowser (dispenser) symbol.

[Wotname]

OK, maybe a current 3YM20 service manual may have the data you need but I have been unable to find / download a free copy. The operation manual clearly shows there is an optional fuel quality sensor with a spare Blue/White wire in the harness for connection to the sensor. See item 19, figure 3 on pages 93 & 94 of this operation manual https://www.yanmar.com/marine/wp-con...M_20240117.pdf

This wire goes directly to the control unit (item 10) where it would be conditioned to illuminate the scale under the Fuel Bowser symbol.

The question then becomes 'what signal level is expected on this wire'; i.e. what standard would Yanmar use?

While there are many types (and 'standards') for fuel level sensors, I would expect Yanmar to use one of the more common standards and given the manufacturing year range of the B20 panel, my guess is that it is not a 0-5V digital input. Likewise I think it is unlikely to be a capacitive fuel level sensor as they are not common on sailing boats.

That leaves me to expect it will be a simple resistive input! Which is good, because that is the easiest to reverse engineer a solution. Reverse engineering is a necessary stock skill for any serial / serious renovator.

Moving on, two common resistive ranges for a resistive fuel level sensor are

A. 240 - 33 ohms (empty to full)
B. 0 - 180 ohms (empty to full).

That said, there are may other ranges available 70-10; 0-90; 0-30 etc.

I would try various resistors between the Blue/white wire and ground (battery -ve) and see what the gauge does. Try say 100 ohms first and see it the instrument responds. If it does, then try something a little greater or smaller. Once the resistive range is determined by experiment, source a sender to suit and job done!

However if it doesn't respond at all to a 100 ohm resistor, I would proceed more cautiously as it just might be expecting a voltage level (somewhere between 0 & 5V).

[Martin G]

Originally Posted by skipperpete

Fuel filter water alarm! If it has a green and red wire to it, otherwise, buggered if I know.
Your project boat looks a lot like my old Harding ships workboat, does it have a 75 hp Mitsubishi diesel and a Kort steerable nozzle?

Thanks for asking Pete,
renovation took place between 2016 and 2018 at Mana Marina New Zealand. The commodore at that time was very generous and let me use for small bucks the hard. She looked miserable almost beyond repair, but when the Ford Diesel came to live we were all shanting. At the first turn the engine blew a half pint of water at us. 70 horse, 4,2 Liter, Ford 5000 tractor engine. Some mentioned Harding, but a kiwi built Marlborough is another option. I believe they were all built during the heydays of lobster fishing. Very strong hulls!
I attach some photos.

[Martin G]

Wotname, thanks for you elaborate thoughts on this issues. Lacking a document about this feature I will follow your suggestion. I believe it is only a low level warning anyway, but after zooming in I was able to see the dashes! Lets see! Keep you updated!

[Wotname]

Originally Posted by Martin G

Wotname, thanks for you elaborate thoughts on this issues. Lacking a document about this feature I will follow your suggestion. I believe it is only a low level warning anyway, but after zooming in I was able to see the dashes! Lets see! Keep you updated!

It might be a low level warning but the little evidence we have so far points towards a quantity gauge.

If it is only a low level warning, then the wire will go to a level switch in the tank. The switch will be open or closed (to ground). Just like the oil pressure or coolant temperature switch (items 33 & 34 on page 94 of the previously mentioned operation manual). Note the manual calls item 19 'a fuel tank level sensor', rather than a switch. The distinction is important! Switches are typically connected to alarms; sensors are connected to gauges.

Furthermore, Yanmar describes the B20 panel as 'The B20 & C30 panels also show some engine alarms and can drive an optional fuel level gauge.' Note the distinction between alarm and gauge. See https://www.yanmar.com/marine/product/panels/b20/

If you find a definitive document, please post it!

[GordMay]

Yanmar Service Manual: 3YM30 - 3YM20 - 2YM15
➥ https://j109.org/docs/yanmar_3ym-2ym-service-manual.pdf


I have NOT uploaded this manual, to our CF 'Library'.

[Martin G]

Thanks Gord,
appreciate the doc. I saw it before. Lots of valuable infos but too old I'm afraid. DOB of my engine is 2014 hence the different panel I guess.

[Wotname]

Thanks Gord, unfortunately the manual you linked does not cover the B20 instrument panel; it only shows the original Yanmar B panel i.e the one shown in post #2.

Now if you can source a later service manual with the B20 panel...we will be ever thankful!

[Martin G]

Hello,
here is a brief update. The Yanmar B20 panel has 4-pin Delphi connector which can be used to connect a fuel gauge. Yanmar recommends Medallion. Without this instrument the tank display in the tacho is defunct. The technician I spoke to recommended a VDO + sensor as an alternative. The pdf attached explains the procedure.

Have a good day

Martin