Yanmar High Temp0 Reading

[sailorboy1]

My 4JH3E temp is reading high. The reading on the gauge has always been high really, but earlier in the year while in Bahamas it pegged high starting a "fire" drill. But the temp on the housing measured about 160F. It has been around 50-100 hours since and the temp never measures hot directly.

I replaced both the sender and gauge. Have tried 2 sensors now including a genuine Yanmar. It still reads 200+ with the housing it is screwed into reading 156-160F.

The gauge tests good. If I ground the wire ro the sender the gauge pegs high. I ran a long jumper wire from the gauge to the sender and it reads the same, so doesn't appear to be an engine harness wire problem.

Ideas?

[bstreep]

We have the opposite problem. Sender alarm goes off, water temp is 75C. Replaced both sensors.



Thought: Swap your sensors on your water pump. Put the temp gauge sensor where the temp alarm sensor is. We are back in the US, and I came up with this for our boat. Our alarm sensor is high on the pump, and I wonder if it gets hotter water hitting it than the gauge. Again, just a thought.

[sailorboy1]

So earlier I tried to fix this by replacing the sender, then the gauge, then the sender agai with an Yanmar sender. Finally I replaced the gauge again but with a $$$ Yanmar gauge and now it reads and works fine. So the Yanmar and aftermarket senders/gauges must be different ohm ranges.

[GordMay]

Gauges and senders are sold as matching sets, generally European or American standard resistance values.

Sender Chart ➥ https://www.cruisersforum.com/galler...r&imageuser=79

Basic Engine Gauge Theory and Testing ➥ https://www.cruisersforum.com/forums....html#post2597

[GordMay]

IIRC: The standard Yanmar engine and panel uses a sender with metric threads, and an impedance/resistance, matched to European instruments.
However, many boatbuilders replaced the standard temperature senders & gauges with American instruments.
The impedance and thread pitch are the critical factors.

Note: Temperature systems [gauge, sender, voltage range] used on boat engines give a general indication of the temperature, in which the sender is operating.

These systems can vary to a maximum ±15°F ➛ 16°F, from actual temperature.

The gauge [itself] is accurate to within about ±5°F, at the mid-scale position.
The sender is accurate to within ±10°F at 200°F. The sender tolerances widen as temperatures become higher, or lower, than 200°F.

Although sender/gauge tolerances rarely run to the maximums, at the same time, the system can possibly indicate up to 15°F difference from actual temperature at 200°F. The accuracy of the system can vary as much as ±16° at 180°F.

These specifications are developed at a system voltage of 14 volts. The sender is also susceptible to “self heating” when electrical current passes through the sender. The self heating causes the sender to become warmer,
than the actual temperature of the fluid [the gauge is compensated for this, effect at 14 volts]. If the system voltage is varied to 13 or 15 volts the gauge may read 5 to 6°F higher, also.

Use of “extenders” or “tees”, for senders, is generally not recommended. This id because: when the sender is moved away from the water flow, the water around the sender bulb tends to run cooler. The gauge will, also, show a cooler reading, than the actual water temperature inside the engine. Also, the amount of weight extended on the fitting of a vibrating engine could cause fatigue-related breakage.

[Wotname]

Originally Posted by GordMay

IIRC: The standard Yanmar engine and panel uses a sender with metric threads, and an impedance/resistance, matched to European instruments.
However, many boatbuilders replaced the standard temperature senders & gauges with American instruments.
The impedance and thread pitch are the critical factors.
.........

^^This is true (well almost true)!

A 'standard' Yanmar engine has JIS threads (Japanese Industrial Standard). Among the many JIS specifications, the two relevant to Yanmar engines are the general fasteners (nuts and bolts) which are metric (course) and the piping threads which are JIS tapered and identical to BSPT. The metric thread is 60 degree equilateral type, the JIS pipe thread (used by Yanmar) is 55 degree isosceles type but many (maybe all?) other JIS pipe threads are 60 degrees.

Regarding gauge senders, the short answer is a 'standard' Yanmar uses BSP threads but some US boats have a Yanmar with NPT threads.

I dunno how US boatbuilders have converted some 'standard' Yanmar engines to NPT threads but I have certainly heard of it happening enough times to believe it is true. Perhaps they order the engines from Yanmar to have NPT piping threads and have US type gauges fitted to the panel.

[GordMay]

Originally Posted by Wotname

^^This is true (well almost true)!

A 'standard' Yanmar engine has JIS threads (Japanese Industrial Standard). Among the many JIS specifications, the two relevant to Yanmar engines are the general fasteners (nuts and bolts) which are metric (course) and the piping threads which are JIS tapered and identical to BSPT. The metric thread is 60 degree equilateral type, the JIS pipe thread (used by Yanmar) is 55 degree isosceles type but many (maybe all?) other JIS pipe threads are 60 degrees.

Regarding gauge senders, the short answer is a 'standard' Yanmar uses BSP threads but some US boats have a Yanmar with NPT threads...

Originally Posted by GordMay

IIRC: The standard Yanmar engine and panel uses a sender with metric BSPT threads, and an impedance/resistance, matched to European instruments...

Thanks, for the clarification/correction, Wottie.

[SailSB]

I have had the same problem since I bought the boat 4 years ago. We are a cat so have 2 4JH4AE engines. One temp gauge reads correct the other reads high to the point of pegging the gauge which then goes to 0, effectively leaving me with no temp gauge on one side. The problem seems to have gotten a bit worse over the years as it pegs out quicker now than it did 4 years ago

I have swapped the sensors side to side, no change, then swapped the gauges side to side, no change. I went ahead and replaced the gauge with a new Yanmar gauge, no change. The only other thing I can thing to do is to replace the wire, but that runs through the bowels of the boat and I am loath to do it.

If I read this thread correctly the gauges and sensors are paired. I'm surprised they're not sold that way if it is important, but I'll try to source a matched pair.

Any suggestions on next steps without changing the wire?

Ken
S/V Snoopin Around
Leopard 46 sailing cat

[GordMay]

Ken:
Having swapped everything, between engines, in the sender/gauge system, your consistent problem seems to be on the engine side.

[SailSB]

Gord,

I agree, but besides replacing the sender, which I have already done, as well as swapping side to side, What else can it be on the engine side?

Ken

[sailorboy1]

Originally Posted by SailSB

Gord,

I agree, but besides replacing the sender, which I have already done, as well as swapping side to side, What else can it be on the engine side?

Ken

wiring, pegging high indicates a grounded wire

[Wotname]

Originally Posted by SailSB

I have had the same problem since I bought the boat 4 years ago. We are a cat so have 2 4JH4AE engines. One temp gauge reads correct the other reads high to the point of pegging the gauge which then goes to 0, effectively leaving me with no temp gauge on one side. The problem seems to have gotten a bit worse over the years as it pegs out quicker now than it did 4 years ago

I have swapped the sensors side to side, no change, then swapped the gauges side to side, no change. I went ahead and replaced the gauge with a new Yanmar gauge, no change. The only other thing I can thing to do is to replace the wire, but that runs through the bowels of the boat and I am loath to do it.

If I read this thread correctly the gauges and sensors are paired. I'm surprised they're not sold that way if it is important, but I'll try to source a matched pair.

Any suggestions on next steps without changing the wire?

Ken
S/V Snoopin Around
Leopard 46 sailing cat

If the problem regularly occurs, try running a temporary external wire from the sender direct to the gauge say through or across the cabin / companionway / passages / etc. Prepare the wire in advance and keep it handy so you can deploy it the next time the fault presents itself. This should determine if the wiring is the culprit or not. I suspect it is.

Originally Posted by SailSB

Gord,

I agree, but besides replacing the sender, which I have already done, as well as swapping side to side, What else can it be on the engine side?

Ken

Originally Posted by sailorboy1

wiring, pegging high indicates a grounded wire

And when it goes to 0, the wire is open circuit.

As a generalisation, the pointer should be at the rest position when the gauge is not powered. When power is applied, the pointer should move slightly above the rest position. As the temperature increases, the pointer should move towards the lowest temperature indication (usually 40C / 100F). If the pointer only moves ever so slightly from the at rest position, then the wire is likely to be open circuit.

Compare both gauges for the pointer movements from a cold power up. Small differences will help the fault finding aspects.

[Wotname]

Originally Posted by GordMay

Gauges and senders are sold as matching sets, generally European or American standard resistance values.
.........

I think there is an error/typo in the Sender Chart. See attached.

[SailSB]

the external wire is a great idea. I can't believe I didn't already try it. I'll do that as soon as I have some extra time.

To be clear on the problem. The "bad" side consistently works at start up, but fairly quickly climbs to the maximum reading, pegs the gauge and then drops out to zero. So it is working, it just thinks the temp is quite a bit higher than it is. If I slow the engine down it cools back down enough just enough to start reading again, but at the extreme high end of the gauge. Often going back and forth from reading high to no reading and back to reading high. So I think the default when it is too high is just to stop reading.
Again, during all these phases of gauge read out, the actual temp as measured by an infrared thermometer at the temp sensor mount is within normal operating range. Low end at low RPM and higher at high RPM.

All I can think of is a high resistance connection somewhere. Skewing the reading.

Ken

[sailorboy1]

Originally Posted by SailSB

To be clear on the problem. The "bad" side consistently works at start up, but fairly quickly climbs to the maximum reading, pegs the gauge and then drops out to zero. So it is working,...............

All I can think of is a high resistance connection somewhere. Skewing the reading.

Ken

It isn't working and pegging high and then dropping to zero doesn't really make sense. A pegged reading is a short and 0 reading is an open. High resistance somewhere would never be a pegged reading.

here is what I think you should look for:

My theory is that you have a water leak on the engine. The reading is fine while the engine first starts up, then the dripping starts to effect the circuit at a wire harness. But that doesn't explain why it would peg, then go to zero.

When I troubleshot mine I also did the run a new wire between the sender and gauge. Just ran outside the harness etc to check that is wasn't a wire etc problem