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Old 18 June 2020, 13:56   #1
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Yanmar 6LP - oil pressure sender/sensor

When I was out the other night I noticed some weird fluctuations on the standard issue Yanmar dash oil pressure gauge, which had always been pretty consistent until then.

Reading around online suggests the sensor/sender units can often fail, and this one has certainly been on the boat ever since I've owned it. Or potentially a bad wiring connection.

I removed the sender unit last night and checked pressure with a mechanical pressure gauge, and all looks good. I then cleaned up all the electrical contacts and wiring and refitted the sender, and the gauge seems to be back to normal today, but I'll try to test out more this evening.

If the sender is on the way out, can I just buy a standard decent quality Euro-resistance 10bar oil pressure sender with the correct (1/8 BSPT) thread, or do I have to have the "special" Yanmar 150+ jobby (119773-91501) to match their gauge?

Thanks,

Paul
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Old 18 June 2020, 14:11   #2
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I've got a Yanmar 4LHA and I replaced the sender with a normal one and it worked fine.

Scrap that - I've just realised that I replaced the gauge as well.
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Old 18 June 2020, 14:39   #3
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Darn it, I was optimistic there for a moment!

Yes, I see loads of Americans replace both the sender and gauge - partly because they want to use their standard NPT senders (with an appropriate adapter), and partly because most of their available gauges are US resistance.

It's slightly unclear from my research so far whether the Yanmar gauge is just standard Euro resistance, or something "special" so you have to use only their senders! Even though the current sender seems to be back to a steady normal now, I'd happily buy a spare for the shelf just in case to minimise any future downtime, especially if I could use a standard VDO/Kus sender unit. For the price, I might just order one and see out of interest...
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Old 18 June 2020, 15:03   #4
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Yanmar guage is not us resistance. I changed my senders to run us resistance faria guages.
I think I still have the origional yanmar senders lying in the boat which were removed when the engines were new I've also got new yanmar dash guages too send me a pm if your interested in buying anything
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Old 18 June 2020, 20:06   #5
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Thanks Ken - have pinged you a PM.

A follow up question after more research tonight as well - do either of you remember if you bought NPT or BSP threaded aftermarket senders?

After last night, I was convinced it was 1/8 BSP, but there seem to be conflicting opinions online as to whether it's NPT or BSP...
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Old 18 June 2020, 21:28   #6
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https://www.asap-supplies.com/faria-...-switch-sd0053

This is what I bought and fitted.
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Old 18 June 2020, 21:42   #7
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As it is a Toyota engine, I wonder if a sender / switch from a Land Cruiser would be a direct replacement?

https://www.roughtrax4x4.com/toyota-...ml#see-details
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Old 18 June 2020, 21:50   #8
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Thanks Guy - did the Faria part fit directly in without any thread adapter?

I'm surprised given how popular this engine is, but after quite a bit of hunting online it doesn't seem clear at all what thread the original Yanmar fitting is, or the resistance of the Yanmar gauge!

Yes, I wondered if a Toyota part would be suitable, but thought this sensor block part was a Yanmar addition, and not part of the original Toyota engine. I could be wrong though.

I shall keep hunting a bit more, now I've started the quest for a replacement backup sender!
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Old 18 June 2020, 22:06   #9
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My engine, which was from a boat with multiple engines, had an odd arrangement of senders and switches. I removed it all back to what looked like original Yanmar and the 1/8 NPT switch / sender screwed into that.

I don't have a picture of what it looks like now. I could take one tomorrow if that is helpful.
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Old 18 June 2020, 22:14   #10
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Thanks - that was a beautiful little Christmas tree of senders and switches you dismantled :-)

1/8 NPT and BSPT seem very close anyway, and it may be someone has successfully screwed (forced) one into the other. I'm just finding far more references online suggesting it's BSPT... All very confusing!

Let me do a bit more research - I may just remove the existing sender again and try to find some appropriate dies/adapters to check the thread.
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Old 18 June 2020, 22:20   #11
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I've now worried myself.

I found the following during a search on line.

Upgrading Yanmar oil pressure gauge and sender - Ocean Navigator - October 2011

I'm going to check mine tomorrow!
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Old 18 June 2020, 22:24   #12
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Yes, that's one of many links I've found, suggesting it wouldn't be an NPT thread originally, and various US companies sell adapters specifically to resolve this issue for Yanmar owners wanting to use the US standard NPT fittings...

Sorry, I didn't meant to worry you though - maybe one of those 'if it works don't touch it" moments!
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Old 18 June 2020, 22:49   #13
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I used npt fittings in my engine & never noticed anything untoward but to be honest I wasn't looking as it never crossed my mind it would be anything but npt. I doubt it would be bsp but even if it were with less than 100psi it would be fine as they are so close to each other anyway. I always install stuff like that with loctite anyway to guarantee a seal (dont like thread tape on that kind of thing).
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Old 18 June 2020, 22:51   #14
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Originally Posted by paulbrown22 View Post
Thanks Ken - have pinged you a PM.

A follow up question after more research tonight as well - do either of you remember if you bought NPT or BSP threaded aftermarket senders?

After last night, I was convinced it was 1/8 BSP, but there seem to be conflicting opinions online as to whether it's NPT or BSP...
No pm arrived
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Old 19 June 2020, 08:10   #15
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Okay, thanks Ken - sounds like NPT works then. For the sake of a couple of pounds I'll probably just order some thread adapters to check the current sender, as there's so many different answers on what the actual thread is here, and then maybe get a standard Euro resistance sender to see whether it works.

I've sent another PM, hopefully this one survives intact!
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Old 20 June 2020, 20:09   #16
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I found another mechanical oil gauge tucked away in the garage today, which claimed to have both 1/8 BSPT and many 1/8 NPT adapters inside. Sadly none of them were engraved or labelled but of the two right angled adapters, which according to the contents one was BSPT and the other NPT, both seemed to fit equally well on the engine and screwed up nicely by hand...

I ran this mechanical gauge for a bit with one of the right angled bends connected, no leaks at all, and double-proved the oil pressures were perfect. I had a couple of hours run out to Swanage this afternoon and the Yanmar gauge is now intermittently working, so definitely looks like a sender on the way out!
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Old 05 July 2020, 20:55   #17
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To close this off, all sorted now thanks to Ken, who sent down a replacement Yanmar sender that works beautifully as hoped. Shows exactly the same pressures as before, so I'm happy the previous sender was on it's last legs after many years of service.

My search for an alternative aftermarket sender that would work with the stock Yanmar dash gauge never finished. I'm still slightly unsure exactly what thread Yanmar use after all my conflicting research, but from my testing against various fittings I think it's 1/8 BSPT, although 1/8 NPT also seems close enough that it goes in smoothly there too.

I couldn't find the resistance/impedance requirements of the Yanmar gauge specified anywhere, but I understand it's not standard Euro or US resistance. I was hoping to try with a VDO sender that Ken also sent down for testing, but sadly that seemed to have a different thread on it that wasn't going into my fittings at all. I did buy some variable resistors and wired up a little test harness to check the Yanmar gauge which gave me the below data if it's of use to anyone else in the future:

0 bar - 87 Ohms
2 bar - 72 Ohms
4 bar - 46 Ohms
6 bar - 25 Ohms
8 bar - 6 Ohms

So it seems "American" in that increased pressure = decreased resistance. I wonder if it's a 90-0 Ohm or 90-5 Ohm sending unit, but whilst I see a few references to those impedance ratings, they don't seem common at all...

Hopefully this latest Yanmar sender will keep going for a while yet, and I won't have to think about it again for another few years!
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Old 05 July 2020, 21:31   #18
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Thanks for the update.
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Old 30 December 2021, 08:56   #19
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Hi Paul, did you formerly own 9m Ribtec “el mono”? If so I now have this boat and currently in the middle of restoration, would be good to know a little of its history.
Best wishes
Steve

Ps - using mobile device and this forum a little clunky - would have pm’d if It was obvious how……… for me it is not!
BW
Steve
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Old 30 December 2021, 10:43   #20
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Hey Steve - yes, that was indeed me, have dropped you a PM.
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