Yanmar Diesel - 2QM15

[dwgifford]

I posted a question on this earlier but I need some more info.
I have a tach for the diesel that reasd exactily half of the actual RPM.
I checked the sensor and put new connectors on them but no luck. Does anyone have any info on taking the wires from the tach direct to the alternator instead of buying a new sensor, which I may or may not need? Or does anyone know what the proper value would be if checking the sensor with an ohm meter?

I also want to run a water temp gage up at the control panel in the cockpit. I already have one down on the side of the engine enclosure. Does anyone have any info on a dual sensor for this? I already have a "T" someone put in the line so I could have the temp sw and one gage on it and don't want to add another fitting if I don't have to.

Thanks.

 

[Paul F]

2qm15

Yes, my 1980 33 has the same engine and I have updated it with a working tach. off the alternator and a temp. gauge. First look at the back of you tach. Does it have adjustment switches? If it does one of the switches may give you the right rpm. If not you can have an alternator shop add the terminals/wires to connect to the tach. That is what I did. An alternator driven tach. is dependent on the size of the belt wheels driving the alternator. I feel mine gives me a fairly accurate reading. Second, at an auto parts store you can buy a mechanical temp. gauge. The one I used is a sunpro. There is not much to them the probe goes into the engine. Your "T" should work as the probe needs to be in the engines cooling water. Then the gauge is installed at the engine control panel in the cockpit. Not much to it, just connect it and it works.

 

[JoelVannordel]

engine temp guage

Yes, my 1980 33 has the same engine and I have updated it with a working tach. off the alternator and a temp. gauge. First look at the back of you tach. Does it have adjustment switches? If it does one of the switches may give you the right rpm. If not you can have an alternator shop add the terminals/wires to connect to the tach. That is what I did. An alternator driven tach. is dependent on the size of the belt wheels driving the alternator. I feel mine gives me a fairly accurate reading. Second, at an auto parts store you can buy a mechanical temp. gauge. The one I used is a sunpro. There is not much to them the probe goes into the engine. Your "T" should work as the probe needs to be in the engines cooling water. Then the gauge is installed at the engine control panel in the cockpit. Not much to it, just connect it and it works.

I have has issues with the water temp gauge in my 37C. The temp sensor is at the highest point in the cooling system so if you are log on water, then no alarm. So I installed a cylinder head temp sensor that bolts onto the head. It gives the true temp of the head with or without water. I know that this is more accurate, I got the gauge and sensor from the surplus center. https://www.surpluscenter.com/home.asp . This gauge runs about 145 on a 3QM30 at 6.5 knots.

The only way to make this better would be to run a sensor with audio alarm so you don't have to watch the gauge all the time and I am looking for that sensor now.

Fair winds and following seas.

Joel

 

[dwgifford]

Re: engine temp guage

Thank you both. I will investigate the tach issue immediately.

 

[coleman]

Much better to run off the flywheel if you can.

Check that the tachometer is correct application for the boat - you mention a previous owner and sometimes they don't get it right. Aftermarket tachometers may be adjustable, but many factory units are fixed for the application (the specific part being the number of features on the reluctor ring/flywheel, and all signal processing that depends on that geometry is internal to the tachometer). If an original tach, get the part number from the tachometer and have a dealer reference.

Another easy thing to check is the gap between the pickup and the flywheel. If the mounting bolts come loose or the unit shifts otherwise, it can give a poor reading. This usually gives twitches that the tachometer's circuitry may or may not damp out, all depends on how they designed it.

Most tachometer pickups are a magnet, a copper wire coil, a piece of iron, very basically that's all. These are not reference/resistance sensors like your temp sender (if electrical) and most of the analog measurements you may have. The units do not fail often and they tend to fail completely. I don't think you have a bad pickup if you're reading reliable and repeatably incorrect values.

I'd guess from what you said that you should check the tachometer gauge head, not so much the pickup and wiring. If you had a spare lying around it would be easy to check this.

 

[John T]

My thoughts

I had the 2QM15 on my old 1980 H30. I'm not sure that it has a flywheel sensor for a tach and I could not find one on my engine. I also added an alternator driven tach and had to adjust the settings on the back of the tach so it read true to the engine RPM. You may have to borrow an RPM lamp or other device to check the RPM. There is an easy method to read RPM using a common AC flourescent lamp. Let me know if you need more info.

RE: the water temp. I successfully changed out the factory water sensor and alarm on my current 3GM30F Yanmar with a CrusPro digital temp gauge (http://www.cruzpro.com/t30.html ). It gives me very accurate temp readings and I still have an overtemp alarm as part of the gauge. I replaced the engine temp sensor with a Telfex unit and tied it into the gauge. It works well. I have heard that the "T" fittings that people install for dual sensors are subject to failure from engine vibration - Check the archives.

 

[coleman]

I sort of threw aside the alternator driven tach when he mentioned "...instead of buying a new sensor" and I assumed that meant there was a pickup. That might have been a leap, I have a 3QM and perhaps they are different back there.

Maybe look for these things to see if they are alike, the 3QM and 2QM. This is from a good site showning how to get in to the flywheel to replace the rear main seal on a 3QM30F (1984 boat). In this photo from their site. You can see a masking tape tag with a wire on the upper port side near the aft of the block. Looks like the tach sensor may be this? it does place directly over the flywheel teeth.

And it looks like this type of old-style tachometer sensor might be what we are seeing on the block in the above photo, though I can't see well enough and that might be a big assumption.