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-   -   Yanmar 3JH3E - Oil pressure drops as RPM's increase (https://www.cruisersforum.com/forums/f54/yanmar-3jh3e-oil-pressure-drops-as-rpms-increase-220621.html)

1boat2many 07-07-2019 18:19

Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Had some work done at Indiantown before starting the trek up towards St. Augustine last week, it's been brutally hot with no wind, so ICW all the way. Day 1 gets us to Stuart, don't notice any problems, but could have been preoccupied by finally being back in the water and moving again (and trying to make the last lock through at St. Lucie by 4:30 PM).
* Day 2, noticed the oil pressure gauge leaning precariously over towards 20, this while chugging along at 2500 RPM (rated max is 3200, so about 75%). Engine hours are low, 525 at start of the trip, with fresh oil and filter change (and fuel filters, and antifreeze flush and fill). Backed off on the RPM's to 2000 and watched the gauge climb to 30ish - just in the green. OK, so now we're doing 4.5 kts and I can live with that.
* Day 3, we have a little current against us and I'm finding @ 2000 RPM the gauge is ticking just over the 20 mark, I drop to 1900, climbs back up around 30ish, we make it a short day. I change the oil and filter that night to be on the safe side.
* Day 4, no better. Did I mention brutally hot? The coolant temp is steady, straight up in the green. Took the engine cover off and directed a fan into the compartment, no appreciable difference, except the cockpit is now a really miserable place to be.
* Day 5, lots of current against us and I'm down to 1750 RPM to just keep the needle at 20. It's a short day, the oil level is a tidge lower than it was.


All along the engine sounds the same, a bit loud, but it always has been, so no change there. Exhaust is clear, oil color is golden, temp is steady. Bad gauge? Oil cooler? Oil pump? Thoughts?

Wotname 07-07-2019 18:25

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Just one thought - engine oil takes a loooong time to reach maximum temperature, easily 40 minutes or more under near full power so the decrease in oil pressure might be due to the high ambient temperature.

An oil change won't hurt!

Lepke 07-07-2019 18:31

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
If you have a mechanical gauge, my first step would be to verify the oil pressure.

Sounds like the oil is really hot. Is the coolant hot, too? Could be a plugged oil cooler, but usually the oil cooler is on the same plumbing as the coolant exchanger. Maybe you have a restriction in the raw water circuit and have a low flow of raw water, collapsed hose, dirty strainer, plugged exhaust loop, bad impeller, thru hull restricted or valve partially closed.

a64pilot 07-07-2019 18:39

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
You can tell oil temp with an IR thermometer and shoot the oil filter.

However I’d guess you have a stuck open oil pressure relief valve.

Even stupid hot oil as in low 200’s shouldn’t drop pressure that much.

sailorchic34 07-07-2019 18:53

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
I would check the electrical wiring if you have a electric oil pressure sender. it would be really strange for the oil pressure to drop with increased RPM. But a bad sender or at loose wire somewhere might cause a electric oil pressure gauge to read low.

If you had a oil cooler I can see possibly a leak in that to seawater, causing low oil pressure as well.

I had a old 3qm Yanmar that exhibited low oil pressure. That was caused by a cracked valve rocker Tower. I will note that you can run the engine all day at 20 psi, with no damage to the engine.

Dave_S 07-07-2019 20:25

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
If you are running low on oil or oil return galleries are clogged or if there is a crack in your pickup tube you may get this.

Compass790 07-07-2019 21:21

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
My guess is oil pressure is dropping because of increased oil temp. You say it's stupidly hot. I'd go with A64 pilot suggestion as to check oil temp with IR thermometer.
Oil temp will climb if you are fighting current, it's analogous to climbing a hill in your car. I would be a little concerned with that oil pressure given the low hours but do you know what the specification is? You dont say what model engine it is.
Agree with Sailorchick that engine can run all day at 20psi, many ancient tractors do.
What was the nature of the work done before you departed?
Has the problem occurred suddenly or has the oil pressure been slowly dropping over mths/years?
You could try a heavier viscosity oil if you cannot find a reason.

Compass790 07-07-2019 21:22

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Sorry engine type in title. Duh!

GordMay 08-07-2019 04:34

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
“Upgrading Yanmar oil pressure gauge and sender” ~ by Harry Hungate
Upgrading Yanmar oil pressure gauge and sender - Ocean Navigator - October 2011

SKU #RM218026 - Oil Pressure Sender for Yanmar Marine Diesel, Replaces: 124060-39452
https://repowermarine.com/index.php/...060-39452.html

1boat2many 08-07-2019 05:42

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Thanks all - I will start by replacing the sender unit, inexpensive and within the range of something I can do (thanks Gord for those links, straight to the part number and an Amazon click away).

The work I had done at Indiantown involved pressure testing the cooling system. The pesky little leak was coming from a drain plug at the oil cooler of all places, on this engine it is just a tubular ring that runs coolant around the base of the oil filter. I wonder if that plug is socked in too tight and threads now obstruct coolant flow. It's a PIA to get to, need to remove the oil filter to get to the plug, so will do that as the next step. I'm also going to get an IR thermometer and start collecting data. Any suggestions on make and model or other fun diagnostic stuff would be great. :thumb:

Wotname 08-07-2019 05:54

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Quote:

Originally Posted by 1boat2many (Post 2926075)
........ I wonder if that plug is socked in too tight and threads now obstruct coolant flow. It's a PIA to get to, need to remove the oil filter to get to the plug, so will do that as the next step. I'm also going to get an IR thermometer and start collecting data. Any suggestions on make and model or other fun diagnostic stuff would be great. :thumb:

Or perhaps too much sealant was used on the threads and has caused some blockage???

Dymaxion 08-07-2019 08:16

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
What weight oil is in it now? Shell Telus T6 in 15W40 might help. It's a diesel rated oil, in synthetic or dino, I'd just use the dino stuff.

dennismenace111 08-07-2019 10:01

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
My thoughts exactly....I'd double check the oil quantity.

sailorboy1 08-07-2019 10:10

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
doesn't make sense to me that the oil pressure goes UP with reducing rpms

I've gone through 2 oil pressure and temp gages the last 8 years

dennismenace111 08-07-2019 10:14

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Pump cavitation!

boatbod 08-07-2019 15:33

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Oil pressure should increase (slightly) as rpm increases. When this doesn't happen it's usually a wiring problem causing voltage drops in the harness (as alternator output increases). Manual oil pressure gauge is the best way to verify. Next best is disconnecting the sender and directly measuring resistance at various rpm.

Compass790 08-07-2019 18:16

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Quote:

Originally Posted by sailorboy1 (Post 2926315)
doesn't make sense to me that the oil pressure goes UP with reducing rpms

I've gone through 2 oil pressure and temp gages the last 8 years

Oil pressure can go up slowly as you reduce rpms ONCE OIL IS HOT as at say 2000 rpm your engine is producing ( for the sake of the argument only) twice as much heat as at 1000rpm. As the oil gets hotter it gets thinner & flows more easily thru the bearing clearances. Pressure is just resistance to flow. Then when you let it run at lower rpms the engine will slowly cool down & oil viscosity will increase which will make the pressure rise
In our engine oil pressure 40 psi @ 1000 rpm cold & 15 psi @ 1000 rpm hot but if we let it run after it's hot at 1000 rpm for 10 mins unloaded it will climb back to 30psi this is running 15w-40 diesel oil. Oil temp after running 2+ hrs under full load is only 59oC & pressure is about 20psi. Engine is raw water-cooled single.
But, I happen to know one of our main bearings has 4 thou clearance instead of 2 thou because some idiot took a little too much off when machining bearing i.d. Ask me how I know.:banghead: That explains partially our below spec oil pressure
It is likely the OP's problem is related to oil temp but if his coolant temp is ok it's a little strange

Compass790 08-07-2019 18:26

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Quote:

Originally Posted by 1boat2many (Post 2926075)
Thanks all - I will start by replacing the sender unit, inexpensive and within the range of something I can do (thanks Gord for those links, straight to the part number and an Amazon click away).

The work I had done at Indiantown involved pressure testing the cooling system. The pesky little leak was coming from a drain plug at the oil cooler of all places, on this engine it is just a tubular ring that runs coolant around the base of the oil filter. I wonder if that plug is socked in too tight and threads now obstruct coolant flow. It's a PIA to get to, need to remove the oil filter to get to the plug, so will do that as the next step. I'm also going to get an IR thermometer and start collecting data. Any suggestions on make and model or other fun diagnostic stuff would be great. :thumb:

If the problem coincided with your pressure testing work I'm with Wotname, check that filter cooling loop & the plug.
But it could be coincidental if it got stinking hot after the work was done

a64pilot 08-07-2019 18:28

Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Really the only way to be sure is to plumb in a direct pressure gauge, which can be an issue because Yanmar uses I believe British pipe thread and not the more common US NPT, they are very close, but there is enough difference so that it won’t quite work.
So getting the proper fitting isn’t easy.

It may be that the OP will have to buy a new sending unit and if that doesn’t fix it, buy a new gauge and if that doesn’t fix it, then it’s an oil PSI problem.
There are way to test both of course but it usually requires a dead weight tester for the sending unit.

Compass790 09-07-2019 00:46

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
I suspect your oil pressure gauge & sender are fine as they are behaving as I'd expect a working system to, BUT I'm an electrical ignoramus. I THINK you are going to have to find the problem elsewhere. Don't have any argument with the idea of checking them first tho as that is easy.
I have successfully screwed a 1/8" NPT male tee into our Yanmars 1/8" female BSP fitting using thread tape without leaks over 200 hrs but you can get an adapter if you want to do it by the book.
Any way keep us posted what you find. My nxt port of call if ambient temps or oil cooler aren't causing yr problems would be pickup tube, as another poster suggested, or oil pump clearances. Dont be shy to shoot me down in flames if it turns out to be sender or gauge.I'm happy to learn from the hive. :-)

Wotname 09-07-2019 01:35

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
To be pedantic, Yanmar uses a Japanese Industrial Standard (JIS) thread however it is a mute point as JIS is interchangeable with BSP.

A male NPT will fit into a female BSP without damage but you will need pipe sealant (as Compass790 posts). Note - the reverse is not true - a BSP male will not fit into a female NPT.

So yes, a common direct pressure gauge with a male NPT will fit the OP's Yanmar engine.

1boat2many 09-07-2019 04:30

Re: Yanmar 3JH3E - Oil pressure drops as RPM's increase
 
Thank you all again for a good discussion! I've shifted my thinking from just fixing the problem to really understanding the problem, taking some accurate measurements (as possible with manual pressure gauge) and posting back results. This may take me a few days, in the meantime, I will be closely watching the low pressure weather system expected to develop in the NE Gulf which could impact N. Florida (northwest coast predicted, but we'll have to see) We are in St. Augustine which is not very far away, so that may drive diagnostics to next week if I have to do something to get out of the way. All that to say that I have less worries about my oil pressure issue now that I understand it better, and that's a big help right now. Will post again once I do the prescribed diagnostics.


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