Oil gauge issues

[CassidyNZ]

Seeing another thread on low oil pressure prompts me to test the general knowledge bank here with a mystery I have had since buying my boat (more than a decade now). Let me outline the symptoms in bullet points:

- When the ignition is off the oil pressure gauge needle resides on the far left side of the gauge as one would expect.

- When turning the ignition on (pre-start), the needle moves to the far right side of the gauge indicating very high pressure.

- When the engine is started, the needle moves to about 3/4 of the way to the left indicating low pressure.

- When RPM is increased whilst cold, the needle moves further left, well into the red sector on the gauge, enough to cause a casual observer some concern. But the buzzer does not sound.

- As the engine warms up, the needle comes to the middle of the gauge indicating “normal” pressure and stays there unwaveringly.

From this I found it obvious that the gauge is working exactly backwards and over the years, I have come to accept that as a fact. What have I done about it so far?

- I replaced the sender unit and the gauge acts exactly the same way except now I’m $350 poorer. So it’s not a sender unit issue.

- I reversed the wires on the back of the gauge thinking “reversed polarity” but the needle violently flicks to the right when the key is turned on and does not move from there when the engine is started or the key is turned off. The gauge has to firmly tapped to dislodge the needle from its new locked position. So it’s not a polarity issue.

The only remaining thing is it must be a faulty gauge but the gauge is integrated into the instrument panel and is not a stand-alone instrument. Replacing it would mean a new instrument mounted somewhere not on the panel which I find unpalatable.

Understand that this has been like this for probably 14 years that I know of and may have been like that for a lot longer. The oil pressure buzzer has sounded only once when, for a known problem, the engine ran out of oil.

Has anyone seen anything like this before and if so, was it fixed and how?

[a64pilot]

Pick one you like, be sure it includes a sender, depending on your engine thread may be an issue, Yanmar I believe is BSP, almost all gauges are NPT, I tapped mine out with an NPT with grease on it catch any metal shavings, very little actual tapping is required, the threads are close, but will not quite work without tapping.
https://www.amazon.com/s?k=Electric+...f=nb_sb_noss_2

Your already $350 into what should be a $25 part, don’t dig deeper buying a new panel etc.
Mount a matching water temp gauge to make it more palatable.
Or pay the OEM price for a new gauge / panel, maybe another $350 or more?

[Wotname]

Engine model?
Is panel mede by the engine manufacturer or by someone else (who)?

$350 for a sender unit - crikey! What brand?

I am thinking the sender unit and the gauge is not compatible and has been that way since new?

Electric oil pressure gauges aren't rocket science so something doesn't jell here.

[CassidyNZ]

@ Wotname - The engine is a Yanmar 4JH2E probably a late 1990’s version. It’s hard to conceive that the original sender unit (I’m guessing the one on the motor when I bought the boat was original) was not matched to the instruments and the replacement I got from the Yanmar agent was identical.

@ a64Pilot - The instrument panel is shown below. As you can see it doesn’t lend itself to adding/supplanting other gauges. Given what the sender unit costs I’m not even going to ask the agents what a new instrument panel will be. Probably would need a mortgage on my home. But a new panel is not required - the gauge is separately removable.

Yes I could pay another bunch of money for a new gauge but I reckon it’ll be expensive. A new rev counter (mine stopped working when it went underwater during a knockdown) is just under $400. I haven’t replaced that either. And the truth is, I don’t know that a new gauge would fix the problem. The sender didn’t and that was as obvious a choice as a new gauge.

I was really wondering if anyone had experience that would prevent me from making the obvious choice of buying a new one. Like I said in the first post, I’ve already got used to reading the gauge backwards and, honestly, it behaves exactly as one would expect from such an instrument, just back to front.

Very curious.

[Wotname]

Originally Posted by CassidyNZ

@ Wotname - The engine is a Yanmar 4JH2E probably a late 1990’s version. It’s hard to conceive that the original sender unit (I’m guessing the one on the motor when I bought the boat was original) was not matched to the instruments and the replacement I got from the Yanmar agent was identical.
.................
I was really wondering if anyone had experience that would prevent me from making the obvious choice of buying a new one. Like I said in the first post, I’ve already got used to reading the gauge backwards and, honestly, it behaves exactly as one would expect from such an instrument, just back to front.

Very curious.

Very curious indeed! I agree with your assessment that the gauge is working backwards - but why???? And yes, a Yanmar sender will be compatible with a Yanmar gauge.

I disagree the sender unit was an obvious choice to replace but that is past history now and I'm not surprised at the price given it was sold by a Yanmar agent (and a NZ one no doubt).

As to why it is working backwards - I wonder if it aways did (i.e. faulty since new) but that sort of seems unlikely OR has it "repaired" by some one else in the past(???).

What do next - you only have three options. Leave it alone, repair it or replace it.

Like you, I think the price will be exorbitant to replace it!

As for repair, it should be easy!!! In essence, the oil pressure meter is simply a voltmeter. As you probably know, when the key switch is off, the meter needle should be resting against the LHS stop. When key is ON (pre start), the needle should move slightly to the zero mark. The fact that your gauge moves fully to the RHS tells me something is reversed or otherwise faulty inside the meter. To confirm, you could disconnect the meter from the panel and reconnect to a seperate 12V supply and run a seperate lead from the sender to the meter. You will need to connect the -ve of the supply to the case of the sender unit of course. If it behaves the same way then you could the swap the lead from the sender terminal to the case and place the -ve lead on sender terminal. If now works correctly, then perhaps a simple wire swap inside the gauge could work. But I would like to see the inside before making any concrete predications

Regardless, the gauge can probably be repaired by any reasonably competent instrument technician. I know of several in Oz so I would presume there would be similar competent guys in NZ.

In all of the above, I am assuming your engine block has the usual common -ve connection to batteries.

[Olly75]

Having been through an oil pressure issue recently, and seeing you are in NZ-

You can get a mechanical gauge from Super Cheap Auto, I think I paid $45, it wont be Yanmar branded, but then its not Yanmar prices! For the fittings go and see Anzor in Whangarei, or call them up and they can get the relevent threaded adapter part that you will likely need. (mine was $6 but they have a minimum order of $10...)

[CassidyNZ]

Originally Posted by Olly75

Having been through an oil pressure issue recently, and seeing you are in NZ-

You can get a mechanical gauge from Super Cheap Auto, I think I paid $45, it wont be Yanmar branded, but then its not Yanmar prices! For the fittings go and see Anzor in Whangarei, or call them up and they can get the relevent threaded adapter part that you will likely need. (mine was $6 but they have a minimum order of $10...)

Thanks - I already knew all that. As you can see from the nature of my instrument panel, a Supercheap oil gauge is not what I want. Oh, and Anzor sell stainless steel fittings which would be the wrong thing to use in this application.

But thanks for the suggestions.

[a64pilot]

Oil pressure sending units work on varying resistance, not voltage.
I’m 99% sure the US and European sending units work backwards from each other.
This is the only place I could find that, but I didn’t look long. Post six I think.
https://www.pistonheads.com/gassing/...&f=8&t=1549652.
I’m also pretty sure that there are different standards for the resistance variance.
A Yanmar manual may describe gauge operation, they are pretty good at theory of operation.
On edit SS fittings would be fine, probably preferable over brass

[Wotname]

Originally Posted by Wotname

.....
..........then you could the swap the lead from the sender terminal to the case and place the -ve lead on sender terminal. If now works correctly, ................

This statement of course is pure horse dung - a total brain fart by me .
I woke up in the middle of the night thinking - why did I write it . It is like saying swap the leads a resistor. Resistors of course are not polarity conscious!

[Wotname]

I am still at loss to to think of a possible explanation for the OP's problem

Is the panel the correct one? Normally I would suggest it didn't matter but there has to be some explanation for the bizarre operation of the LOP gauge.

My 4H2E service manual (dated April 2001) shows four panel options (B2, C, D & E), none of which is the same as the OP's panel. However this is hardly definitive. One would expect the LOP gauge to operate the same manner across the Yanmar range, only a careful perusal of the Yanmar parts book would make it definitive.

Is there a different Yanmar sender that matches the OP gauge or conversely is there a different Yanmar gauge that matches the OP's sender? While unlikely, it is possible!

IMO, it is safe to say - the gauge should not operate backwards, therefore the LOP metering system is faulty.

That leaves me thinking -
either
the gauge has been faulty since new
or
the gauge has been repaired incorrectly in the past
or
the gauge has developed an internal fault that gives this bizarre operation
or
This Yanmar sender is not compatible with this Yanmar gauge.

None of these are common faults and any one of them would be considered to be highly unlikely yet here we are.......considering the improbable!

Ay one got a better explanation ??????

[Wotname]

Originally Posted by a64pilot

Oil pressure sending units work on varying resistance, not voltage.

That is mostly correct and certainly correct for the common engines we are considering. The sender varies it's resistance according to the pressure applied. The gauge will be registering this as a varying voltage or current (dependant on design). See below for further detail.

I’m 99% sure the US and European sending units work backwards from each other.
This is the only place I could find that, but I didn’t look long. Post six I think.
https://www.pistonheads.com/gassing/...&f=8&t=1549652.
I’m also pretty sure that there are different standards for the resistance variance.

Yes there are many "standards" and finding the detail is often hard without access to manufacturer's data. It is out there somewhere on the net though! The link you provided does strongly suggests the OP's Yanmar sender is not compatible with the OP's Yanmar gauge. Very odd but possible

A Yanmar manual may describe gauge operation, they are pretty good at theory of operation.

Yes some Yanmar manuals are very explicit with detail on such matters. Unfortunately my Yanmar 4JH2E manual isn't one that provides great detail. It simply details the electrical aspects as a resistance switch (sic) with a max operating pressure of 113.76 psi. Part number 144626-91560. It gives no detail about the gauge.
On edit SS fittings would be fine, probably preferable over brass

FWIW, the pointy part of the gauge is an analogue meter movement. The meter movement measures an electromagnetic field. That electromagnetic field is created by current flowing though the meter movement (usually in the order of a few hundred microamps). The two common types of meter movement are a moving coil and moving iron. Moving coil is more sensitive but delicate. Moving iron is more robust but less sensitive. Both types can be found in an analogue gauge.

So technically all these movements measure current flow only but we designate them as either voltage meters or current meters depending on the outside circuit parameters we wish to measure. It simply the arrangement of resistors associated with the movement that determines how it is scaled.

The sender unit varies it's resistance according to the pressure applied. At this point, the gauge can de designed to simply measure the varying current flow though the sender unit but more commonly the gauge can be designed to measure the varying voltage across the sender unit. Better quality gauges will buffer and amplify the varying voltage across the sender unit.

[CassidyNZ]

Originally Posted by a64pilot

Oil pressure sending units work on varying resistance, not voltage.
I’m 99% sure the US and European sending units work backwards from each other.
This is the only place I could find that, but I didn’t look long. Post six I think.
https://www.pistonheads.com/gassing/...&f=8&t=1549652.
I’m also pretty sure that there are different standards for the resistance variance.
A Yanmar manual may describe gauge operation, they are pretty good at theory of operation.
On edit SS fittings would be fine, probably preferable over brass

Thanks for the link. That thread exactly defines my situation. The verdict seems clear cut but no solution is offered other than switching terminals on the sender unit. That doesn’t help me - my sender only has one wire.

I have the original manual and it doesn’t have anything that covers my situation.

@ Wotname - the C panel in the manual is the one I have. The “picture” is a bit rudimentary but it is the same panel as the one I posted above. As far as compatibility goes, I understood from the PO that the boat originally had a Volvo in and was repowered at some point with the Yanmar. No doubt the panel was supplied with the new engine.

Whilst now being cognisant of the difference between US and Euro standards, I would be amazed if one manufacturer produced two different versions simply because of the markets they may be sold in. And the agent that sold me the new sender never considered there could be a difference.

Of course, these comments could hold the solution but exactly what that solution is remains a mystery. Maybe a question directed at Yanmar themselves could hold the key. I’ll have a look at that.

[a64pilot]

You didn’t read I believe it was post 6.
It’s not a reverse polarity thing nor it is it a swapping wires thing.
What it is is that one standard reduces resistance with increasing pressure, the other standard increases resistance with increasing pressure.

Having the wrong standard sending unit will make the gauge work in reverse, apparently. I have never personally seen this though.

Finding what you have is simple with a multimeter, simply measure the resistance with the engine off and with it running.

However the next problem is finding a sending unit the first works in the correct direction and secondly has the correct resistance values.

[Wotname]

To reiterate what I and a64pilot posted earlier - resistance is not polarity conscious so nothing about the sender wiring can be swapped!

[Wotname]

Originally Posted by CassidyNZ

Thanks for the link. That thread exactly defines my situation. The verdict seems clear cut but no solution is offered other than switching terminals on the sender unit. That doesn’t help me - my sender only has one wire.

I have the original manual and it doesn’t have anything that covers my situation.

@ Wotname - the C panel in the manual is the one I have. The “picture” is a bit rudimentary but it is the same panel as the one I posted above. As far as compatibility goes, I understood from the PO that the boat originally had a Volvo in and was repowered at some point with the Yanmar. No doubt the panel was supplied with the new engine.
............

Are you looking at the original operation manual or the service manual. I only have the service manual and it shows this as a C panel which is slightly different to the panel picture you posted - more mysteries .

It is not beyond the bounds of possibility than Yanmar made a mistake and supplied the wrong panel with the engine - again highly unlikely but still possible.

I wonder who installed and commissioned the engine or was the panel replaced for some reason after installation or...

You certainly have posted a curly problem!