Oil Pressure Switch vs Oil Pressure Sender

[geoffschultz]

Last night we were on a 190 nm passage from Manzanillo, Mexico to Ixtapa. Just as I was about to come on the 3 AM shift, the oil low pressure alarm went off. I raced up and looked at the panel and I could see that the pressure gauge was reading correctly. When I changed the engine RPMs, the pressure did what I expected it to do. We had a little wind, so we put up the sails and sailed at 2-3 kts. I checked the engine oil levels and they were fine.

Amazingly we had very limited Internet access and I texted Dave Balfour, who's a great friend and was responsible for commissioning BlueJacket when he worked at Freedom, and described the issue. He said to believe the pressure gauge and not the idiot light. What wind we had finally died and I fired the motor back up. The light was on, then went off as expected, and then a minute or so later flickered on. We ran with it on for hours and then it suddenly went out.

I replaced the oil pressure switch in 2011 by accident. I had wanted to replace the sender unit but the part # in the manual was wrong. Unfortunately I didn't keep the old switch.

This is on a Yanmar 3JH2-TE. Note that the oil pressure sender and the pressure switch take their readings from basically the exact same location.

Anyhow, the area where we're at is basically devoid of marine services and we have 600 miles to go along some pretty desolate coast. I might be able to find a diesel mechanic in Acapulco, but I'm not sure. Scary thought!

Does anyone have any experience with something similar?

-- Geoff

 

[Bill Roosa]

If one or the other is indicating the oil pressure is ok I'd be comfortable that there is in fact oil pressure. You can probably wait till you get to a location where you can order the part.

 

[centerline]

what Bill Roosa said!....

Or... you should be able to go to any autoparts, equipment or tractor store and get an oil pressure switch. they are a common part. they usually have 1/8MPT threads to be used on any engine that was intended to be sold and installed in the US, but some have metric threads...
they have different operating ranges and operating modes such as normal open or normal closed... I would think you would want a normal closed switch in the 15-20 lb range...
that would allow at least 15lbs of oil pressure to hold the contacts open and the electrical circuit is broken so the light remains off. if the oil pressure drops below 15lbs, the internal spring closes the contacts causing the lights, bells and whistles to activate.

 

[Charles Erwin]

The threads in the Yanmar motor block switch port are 1/8 BSPT (British Standard Pipe Tapered frequently called metric.) 1/8 NPT (National Pipe Tapered) does not have the same number of threads per inch as 1/8 BSP and the thread form shape (peak and valley) are also different from BSP threads

These 1/8 fittings will engage one another and no doubt many people do so but thread mismatches should be avoided. Adapters are available ie BSP to NPT. Pressure switches from Japanese products (cars, tractors, etc.) will probably be BSP threads.

Try to get the switch with the correct thread. Meanwhile make sure the wire from the idiot lamp to the sender switch is not contacting the block because contact will cause intermittent lamp on condition.

Charles

 

[zeehag]

hello bluejacket--i heard folks calling ye on vhf. i am in bahia zihuatenejo for only a few more days. sorry to hear your woes....seems all of us have them by this area of world--everyone comes in with difficulties--

i have 2 sets of gauges--one set inside boat which are mechanical , one set outside boat which are electrical, for just this happening, so i can compare both and see what is truly happening. hopefully.

i had , before failure, both mechanical and electric gauges, fully functional, now we create an electrical gauge for cockpit readability....

..do you have a source for parts?? we have found many places with the ingredients for the parts...if you want to speak with my friend, he will return to my boat within a few more days--he i making the fabricated stuff on my formosa..awesome smart boatwright.

 

[geoffschultz]

Zehag, we're at Isla Ixtapa having a great time. We'll be in Z-town in the next few days. When are you leaving?

Rest: The biggest issue that I have with getting an oil pressure switch is that I don't know what the correct PSI rating is for it. I have an oil pressure switch for my generator, but I have no idea what the PSI rating is for that one. Since the engine for the generator is a Kubota, I'm guessing that it uses BSPT/metric threads.

Thanks for all of the advice, Geoff

 

[Charles Erwin]

Geoff

Any switch will do. All the switch/lamp warning amounts to is an alarm which says you have oil pressure or you do not. The purpose of this is to back up a low pressure trend so you get second chance in case the on-watch person does not notice declining oil pressure. They are all of them at least 5psi anyway. So you immediately can see that these are not really engine specific. You could even swap the Kubota sender with the Yanmar as experiment if you are otherwise bored.

Meantime did you check your present sender wire for chafe? Did you check the present sender switch orifice to rule out a spec of trash might be lodged therein?

Charles

 

[geoffschultz]

I just did some more research and found out that the part for my generator is a 10 PSI 1/8" NPT thread. I also read my Yanmar service manual and found out that the oil pressure regulator is set to 50-64 PSI, but I don't know what the pressure switch setting is for the Yanmar part. But, this is a good start.

Zehag: Do you know if there is an auto parts store in Zihuantanejo?

-- Geoff

 

[Charles Erwin]

The oil pressure regulator is irrelevant. That system is expressly to overcome a completely fouled oil filter.

Charles

 

[zeehag]

geoff--i will be here until after my mechanic returns. i will allow you to borrow him if you still need to ..he is excellent mechanic. he just needs to get here by bus from barra de navidad--i am getting my final hull cleaning here on the 24th, and should hopefully be going north from here very shortly thereafter.
if you use hull cleaners, use augie--he good, inexpensive, reliable. he swims to boat and doesnt run scams.
daniel is good for topside work. con abreojos.

when you come in here--i am the one in the dead center of the playa madera anchorage with the 160 ft chain set from south to north..lol.....my boat looks a lil rough, as she is being refit...but from 100 ft she be awesome...

 

[centerline]

oil pressure switch for the idiot light should be no less than 12lbs.... as long as you have at least some oil pressure the engine is being lubed.

if you get one that is in the 30lb range, it will probably be fine as long as the rpm is up on the engine, but when it returns to an idle, the oil pressure may drop to 28psi and trip the switch, even though nothing is wrong....

all the switch needs to do is trip the warning system when you lose oil pressure.... it does not determine whether 18psi is when you should start to worry or if 25psi is when it should trip the warnings... or 40psi.... it isnt supposed to know the condition of your engine.... all it it is suppose to know is when it doesnt have oil pressure.
but at 10-15 psi you may get a warning in time to figure out what to do before you have no oil pressure at all.

 

[geoffschultz]

The oil pressure regulator is irrelevant. That system is expressly to overcome a completely fouled oil filter.

You are correct. What is the normal operating oil pressure?

-- Geoff

 

[zeehag]

there are many places to obtain auto an d out special neds parts--autozone, and some without actual names. they are all located together on th esame street. we were able to find a gauge in bucerias, and now, we are tryng to finish installing it--is the one for cockpit reading. mine is a second gauge--my mechanical one in main saloon still works well. we needed some tubing, fittings, etc--will be adding it here in the bay before we leave for barra...

what is name of your boat?????

 

[centerline]

You are correct. What is the normal operating oil pressure?

-- Geoff

you have already determined the regulator is set to 50-64psi..... if the oil pump is strong and your engine is tight, it will be up there against the regulator.

if the engine has extreme wear on it and/or the pump is getting weak, it can drop to 8-10psi at an idle.... and still be fine.

25-40 psi is an average normal.... more oil pressure doesnt necessarily make it better, the engine can be lubed fine with 5lbs of pressure if there is enough flow....

 

[kloudie1]

The typical switch is normally set for very low pressure.. on the Yanmar 3GMF, for instance, the switch set point is 1.4 to 4.3 psi.. very low.. If the gauge is wiggling and acting like it is telling the truth, Press on until you can get another switch.. watch the gauge.

 

[Charles Erwin]

Yanmar might publish these values. As for me - I would not be concerned with normal low at 15-20 at full hot, idle. Obviously age -main bearing clearance wear, using multi or single grade oils, coolant temperature - controlled by the thermostat and coolant pump flow - will have an effect on what one regards as normal oil pressure.

So the oil pressure (idiot lamp) alarm needs to go off 5 or higher but obviously not 15. This is why I figure the trip value is pretty much irrelevant considering you have pressure gauge.

Clearly a 1/8 BSPT male - 1/8 NPT female adapter and a 10 PSI NPT switch would work, it's just that you may not find such at your location. Even if so, the adapter/sender assembly might not fit in the space you have. Maybe consider you get friend to mail genuine article from US dealer, obtain Yanmar tractor motor sender at your location, or get a thread match at auto supply. All this after you test the present sender by clearing any trash from the orifice.

Charles

 

[zeehag]

as no one wishes to be in zihuatenejo bahia in summer, it is a good idea to find something nearby and make it work until you can get to a safe harbor for summer season...time is short now---no time for mail in mexico to arrive. is why i offered up my assistant/slave/bn/genius friend....
.ixtapa marina reportedly is pricey, and has a lot of cocodrilos...especially with rainy season, i have been advised, but that is a part of an adventure.
would be a place to ride out storms and wait for mail...

there are things,-parts, here--ye just have to know where to look--isnt like going into xyz marine or ace hardware down here---as we are doing just this exact thing, my friend can prolly help a lot, if you can wait until his return in a coupla few days....

 

[Maine Sail]

I just did some more research and found out that the part for my generator is a 10 PSI 1/8" NPT thread. I also read my Yanmar service manual and found out that the oil pressure regulator is set to 50-64 PSI, but I don't know what the pressure switch setting is for the Yanmar part. But, this is a good start.

Zehag: Do you know if there is an auto parts store in Zihuantanejo?

-- Geoff

But your Kubota block likely has a BSP/JSI to NPT adapter that the 1/8" NPT switch threads into, many of them do.

Kubota and Yanmar blocks are BSP/JSI tapped for oil senders etc.. Be sure, if you use an NPT switch, that you use an adapter to make it work correctly. The threads per inch and thread pitch are different between BSP/JSI and NPT...

Often times these can be fixed by a simple R&R and cleaning of the hole. Takes about five minutes...

 

[geoffschultz]

Everyone, thanks for the feedback. I'll figure something out tomorrow when people are back to work & I can get some e-mail responses.

zeehag: I'm on BlueJacket.

 

[Maine Sail]

Geoff,

I am pretty sure the PS100 is a switch I have used before to fix Yanmars. I got it locally for about $8.00...

http://www.autozone.com/autozone/parts/_/N-5yc1s?itemIdentifier=123844