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Old 25-01-2021, 10:09   #1
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Need help with water temp sensor install on Yanmar 3YM30

I want to install water temperature sensor/senders on my Yanmar 3YM30s. I have the temp senders, properly threaded as well as appropriate Stewart Warner analog gauges. The question is where to install them on the engine. I want to keep the temperature switch that activates the warning light. A respected Yanmar tech in Ft. Lauderdale told me NOT to install them on a "T" along with the temp switch as this will negatively effect the accuracy of the switch. A post on this forum in 2019 echoed this advice. "Do not use a tee for the temperature sensor. The sensor should protrude into the water passage or it will affect its reading. Additionally the location of the sensor is important as well. Ideally the sensor is very near the thermostat." The Ft. L tech recommended looking for a plugged/unused port on the block or the water pump for the install. There are two possibilities on the water pump, as seen on the schematic attached. One is on the upstream side of the thermostat housing, the other is lower and to the left on the water pump housing itself. I'm thinking the one on the thermostat housing might be the preferred location. I have also attached other schematics showing water flow direction and other details that might assist in providing input. Suggestions?
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Old 25-01-2021, 14:20   #2
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Re: Need help with water temp sensor install on Yanmar 3YM30

Here ya go!!!
https://www.speedwaymotors.com/Speed...or%20the%20fan

Runs off the signal to your analog gauge, only need one sensor in the block.
Use the fan output to light the .idiot light

When I built my hotrod 25 years ago, I had to invent and build my own. Now that there's no Radio Shack, I probably couldn't make another, even if I could remember how.
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Old 25-01-2021, 14:42   #3
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Re: Need help with water temp sensor install on Yanmar 3YM30

You need to know the direction of water flow through the thermostat. The sending unit needs to be on the engine side of the thermostat. By your drawings that looks like it would be the water pump.
Reasoning is that if the thermostat sticks (which happens) the engine will overheat, but your sending unit will stay in the cooler water on the other side of the thermostat and not show the overheating condition.
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Old 25-01-2021, 15:56   #4
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Re: Need help with water temp sensor install on Yanmar 3YM30

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Originally Posted by Nani Kai View Post
........ There are two possibilities on the water pump, as seen on the schematic attached. One is on the upstream side of the thermostat housing, the other is lower and to the left on the water pump housing itself. I'm thinking the one on the thermostat housing might be the preferred location. I have also attached other schematics showing water flow direction and other details that might assist in providing input. Suggestions?
Essentially you want the gauge sensor in the same section of water flow as the light/alarm switch. From the information posted there are three unused / plugged ports but only one of them appears to be at the same water temperature as the light/alarm switch.

I have marked this one with a green circle.

The other two marked with red circles are (I believe) ports for an off engine hot water system.
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File Type: pdf Yanmar water page 183.pdf (142.3 KB, 50 views)
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Old 26-01-2021, 02:37   #5
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Re: Need help with water temp sensor install on Yanmar 3YM30

Does anyone know what thread the green tapping identified by Whatname is? I am looking to install a 2 channel temperature alarm for each of my 3YMs, one channel coolant temp, the other exhaust temp downstream of the water injection elbow.
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Old 26-01-2021, 03:35   #6
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Re: Need help with water temp sensor install on Yanmar 3YM30

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Originally Posted by Rapanui View Post
Does anyone know what thread the green tapping identified by Whatname is? I am looking to install a 2 channel temperature alarm for each of my 3YMs, one channel coolant temp, the other exhaust temp downstream of the water injection elbow.
Yanmar normally uses BSP threads and my guess is it will be 1/4" BSP.
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Old 26-01-2021, 06:53   #7
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Re: Need help with water temp sensor install on Yanmar 3YM30

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Originally Posted by Wotname View Post
Yanmar normally uses BSP threads and my guess is it will be 1/4" BSP.
IIRC, most senders are 1/8" pipe size, to Japanese Industrial Standard JIS B 0203, which is identical to British Standard [BSPP or BSPT?] and DIN which have a thread angle of 55° and 28 threads per inch in the 1/8-inch pipe size.

See also ➥ https://www.cruisersforum.com/forums...ml#post1633530
And ➥ https://www.cruisersforum.com/forums...ml#post1629623

I should have checked, before I posted.

Apparently “JIS B 0203" threads are Tapered.
https://yuken-usa.com/pdf/special/JI...pe_Threads.pdf
http://spokanehose.com/product.php?id=5096

VDO senders, for instance, come with (both) 1/8"-27 and 1/4"-18 (& other) Tapered threads.
https://www.vdo-gauges.com/media/ins...%20Senders.pdf
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Old 26-01-2021, 08:01   #8
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Re: Need help with water temp sensor install on Yanmar 3YM30

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Originally Posted by Bill Seal View Post
Here ya go!!! [/URL]
Runs off the signal to your analog gauge, only need one sensor in the block.
Use the fan output to light the .idiot light
If I understand correctly I would install the temperature gauge sensor in the port where the temperature switch is located, dispense with the temperature switch altogether then use the adjustable fan speed signal to light the alarm LED at the helm. The only problem I see with this is getting the temperature signal (nee fan speed signal) adjusted properly for the idiot light to go on at the correct setting.

Finding a suitable, unused port for the temperature gauge sensor would be the easiest and most direct without any additional expense, however, if for some reason that is unsuccessful I will keep your suggestion in mind. Thanks for taking the time.
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Old 26-01-2021, 08:06   #9
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Re: Need help with water temp sensor install on Yanmar 3YM30

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Originally Posted by wholybee View Post
You need to know the direction of water flow through the thermostat. The sending unit needs to be on the engine side of the thermostat. By your drawings that looks like it would be the water pump.
Reasoning is that if the thermostat sticks (which happens) the engine will overheat, but your sending unit will stay in the cooler water on the other side of the thermostat and not show the overheating condition.
I understand fully. The diagrams from the manual don't show quite enough to confirm the water flow to the 3 possible ports. It will have to wait until I can get back to the boat and examine more closely, post vaccination, sometime in March I hope. Thanks for confirming what I had surmised from looking at the placement of the thermostat.
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Old 26-01-2021, 08:38   #10
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Re: Need help with water temp sensor install on Yanmar 3YM30

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Originally Posted by Wotname View Post
Essentially you want the gauge sensor in the same section of water flow as the light/alarm switch. From the information posted there are three unused / plugged ports but only one of them appears to be at the same water temperature as the light/alarm switch.

I have marked this one with a green circle.

The other two marked with red circles are (I believe) ports for an off engine hot water system.
It appears to me you are right about the green circled port. I will confirm that when I get back to the boat in March. I was going to have a mechanic do the install this week in my absence but after the responses received here I think it best to confirm everything myself. Your second conclusion about the off engine hot water system is also correct, I believe. I wondered what the "hot water inlet and outlet" notes referred to on the schematic in relation to these ports. I may use this info to install a second hot water shower on the starboard side sugar scoop. Thanks a bunch.
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Old 26-01-2021, 12:00   #11
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Re: Need help with water temp sensor install on Yanmar 3YM30

I'm no mechanic but had no trouble in installing a temp sensor in the exaust water pipe up stream of the elbow. The only complication is that I had to rotate the temp indicator 90 deg to fit my panel. The time lag between hot exaust and hot radiator is negligible.
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Old 26-01-2021, 12:55   #12
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Re: Need help with water temp sensor install on Yanmar 3YM30

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I'm no mechanic but had no trouble in installing a temp sensor in the exaust water pipe up stream of the elbow. The only complication is that I had to rotate the temp indicator 90 deg to fit my panel. The time lag between hot exaust and hot radiator is negligible.
Exhaust temperature alarm is valuable and possibly more important than an engine heat sensor.
The exhaust heats far faster than the motor if cooling water stops flowing so this gives plenty of warning before damage occurs.
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Old 26-01-2021, 18:43   #13
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Re: Need help with water temp sensor install on Yanmar 3YM30

i know you already have your equipment, but they make a sensor that goes on the outside of the exhaust that sounds a loud buzzer when the exhaust heats up too much ( loss of cooling water flow) but prior to meltdown- put one on my engine in less than hour including running lines to the binnacle for the buzzer/siren. very easy and just as useful.
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Old 27-01-2021, 08:27   #14
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Re: Need help with water temp sensor install on Yanmar 3YM30

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i know you already have your equipment, but they make a sensor that goes on the outside of the exhaust that sounds a loud buzzer when the exhaust heats up too much ( loss of cooling water flow) but prior to meltdown- put one on my engine in less than hour including running lines to the binnacle for the buzzer/siren. very easy and just as useful.
Thanks to Madehn, adjo and Dave229 re: exhaust temperature option. I'm not sure that will provide me with the information I need. If after reading my comments below you feel that the exhaust temperature will address my concerns, I would welcome your input.

The existing alarm light at the helm will tell me if there's a critical problem requiring engine shutdown so just a buzzing alarm won't add anything. What I want in addition is an indication that a problem might be arising which a temperature gauge will provide. e.g. It occurs to me that an impeller that is failing might be indicated by a higher than normal operating temp. As might also occur with reduced water intake due to some minor blockage. I also want to compare engine temperatures at various RPM loads to determine where the engine is most comfortable. Lastly, I want real time data in the event of an emergency to determine if I am pressing the engines too hard or if I can squeeze another 500rpms out of them. I had a situation last cruising season with a very large Navy vessel bearing down on us requiring me to throttle all the way up, or at least as far RPM wise as I felt was safe. An engine temperature read out would have told me how close I was to "red line" which would have helped.
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Old 27-01-2021, 15:23   #15
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Re: Need help with water temp sensor install on Yanmar 3YM30

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Originally Posted by Nani Kai View Post
Thanks to Madehn, adjo and Dave229 re: exhaust temperature option. I'm not sure that will provide me with the information I need. If after reading my comments below you feel that the exhaust temperature will address my concerns, I would welcome your input.

The existing alarm light at the helm will tell me if there's a critical problem requiring engine shutdown so just a buzzing alarm won't add anything. What I want in addition is an indication that a problem might be arising which a temperature gauge will provide. e.g. It occurs to me that an impeller that is failing might be indicated by a higher than normal operating temp. As might also occur with reduced water intake due to some minor blockage. I also want to compare engine temperatures at various RPM loads to determine where the engine is most comfortable. Lastly, I want real time data in the event of an emergency to determine if I am pressing the engines too hard or if I can squeeze another 500rpms out of them. I had a situation last cruising season with a very large Navy vessel bearing down on us requiring me to throttle all the way up, or at least as far RPM wise as I felt was safe. An engine temperature read out would have told me how close I was to "red line" which would have helped.
Nani Kai, let's review engine cooling 101 and apologies if I am posting stuff you already know.

TL-DR - gauge only tells you if the coolant is too hot, it doesn't detect cooling defects that can catastrophically impact the exhaust system.

The temperature gauge only measure the coolant temperature and this is the last thing to change if a cooling fault develops. The coolant temperature is dependent of the thermostat, the coolant pump and the raw water (RW) cooling system. There is a fair amount of hysteresis in the total system, i.e. a delay between an issue and the response of the temperature gauge.

The coolant temperature should never exceed the fully open thermostat setting i.e. even when running at max rpm continuously, the temperature should remain constant at or below the thermostat rating. If the temperature starts to rise above the thermostat rating, there is an defect somewhere in the cooling system (coolant or RWC).

If you are using the temperature gauge to detect cooling faults, the following aspects should be noted.

1. Slowly developing issues (e.g. partially blocked heat exchanger or worn RW pump etc) will first show up (i.e. temperature rising above thermostat rating)
when operating at max rpm. At lower power settings, the temperature will remain normal until the defect gets worse (usually it has to get much worse).

2. Rapidly developing issues (e.g. blocked RW inlet) will not be detected by the gauge until after other serious problems develop - for instance exhaust system failure (burnt exhaust pipe / melted watercock etc).

So yes, an engine coolant temperature gauge is a handy tool to have and can help to detect slowing trending cooling system faults but won't detect rapidly occurring faults that might destroy the exhaust system.

IMO, the best (and still simple) arrangement is a coolant temperature gauge AND an exhaust temperature alarm.

While there are several types of exhaust temperature alarms, the Vetus one is probably the easiest (but not the cheapest) to install. Of course, an exhaust temperature alarm won't detect all slowly developing cooling faults, you need a gauge for that ()

https://www.vetus.com/en/exhaust-sys...struments.html
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