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Old 09-04-2015, 14:35   #16
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Re: Low oil pressure reading

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Originally Posted by Tayana42 View Post
Thanks for the reply. Seems to confirm, 3000 rpm @ 41-78 psi but I'm still uncertain about running at 2000 rpm at 40 psi for long hours. Or should I interpret this to mean I should only cruise at higher rpm?


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Old 09-04-2015, 14:36   #17
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Re: Low oil pressure reading

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I means you are just worrying yourself crazy.

Probably right. I do that.


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Old 09-04-2015, 14:36   #18
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Re: Low oil pressure reading

40 isn't low oil pressure in my book for most engines, get much below 30 though and I'd begin to be concerned.
What oil are you running? Viscosity has a lot to do with pressure


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Old 09-04-2015, 14:42   #19
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Re: Low oil pressure reading

A64pilot, thanks for that. I'm running 15-40 oil.


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Old 09-04-2015, 15:00   #20
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Re: Low oil pressure reading

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A few of weeks have gone by and we finally got the mechanical oil pressure gauge installed. It is a Murphy model 20P-150. The engine is a Yanmar 4JHE naturally aspirated.

At idle the gauge reads 30 psi. Under load at 2000 rpm it goes to 60 psi. All good. However, after about an hour of running at 2000 rpm the pressure drops to 40 psi. Increased engine rpm to 25000 and pressure reading was 50 psi. I didn't keep it at 2500 long. This is the same pattern as the electronic gauge readings that caused me to install the mechanical gauge.

My mechanic, who I've used for years, says it okay. He says 2000 rpm is the bottom of the cruising range for this engine and 40 psi is good. I'm happy to take him word for this...but I wouldn't mind some input from the forum. Is 40 psi okay for the Yanmar 4JHE at 2000 rpm?


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Old 09-04-2015, 15:40   #21
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Re: Low oil pressure reading

I have the same engine. The oil sender quit after about 2 years, reading about half what it should have. I put a mechanical gauge below in the engine room, with a heavy-duty hose, just to make sure what the oil pressure was. The electrical gauge in the panel was replaced with an automotive gauge kit that cost $35 including the matching sending unit. Yanmar wanted over $100 just for the sender. It doesn't match perfectly, but I wouldn't pay the difference.
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Old 09-04-2015, 15:45   #22
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Re: Low oil pressure reading

Svinshallah, thanks for your response. I did replace the oil sending unit before adding the mechanical psi gauge. It wasn't the problem in this case.


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Old 09-04-2015, 16:14   #23
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Re: Low oil pressure reading

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I[t] means you are just worrying yourself crazy.
+1. If 41 is normal at 3000 rpm I would expect a little less at 2000. And one pound is a very little less (is the gauge even that accurate?).

The warning setpoint is a mere 0.5 kg/cm2 = 7 psi. There's usually margin on the warning, so I'd be quite content with 40 @ 2000 rpm.
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Old 09-04-2015, 16:54   #24
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Re: Low oil pressure reading

The fact that it starts out high then pressure drops as the oil gets hot sort of rules out the pressure relief valve. Might be worth checking oil temp by use of an IR thermometer pointed at the oil pan, if you have an oil cooler its unlikely but possible that it's not working as well as it should and you could have high oil temp. High oil temp of course is a cause for low oil pressure.
If that's not it, I'd try straight 30W oil, but I don't think you have a cause for alarm, at least not for a very long time
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Old 09-04-2015, 17:17   #25
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Re: Low oil pressure reading

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Spec oil pressure is 10 psi at idle, and 40-70 psi at 3300 RPM, according to the service manual.
Different engine but your oil pressure is perfectly normal.
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Old 09-04-2015, 22:42   #26
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Re: Low oil pressure reading

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Originally Posted by a64pilot View Post
The fact that it starts out high then pressure drops as the oil gets hot sort of rules out the pressure relief valve. Might be worth checking oil temp by use of an IR thermometer pointed at the oil pan, if you have an oil cooler its unlikely but possible that it's not working as well as it should and you could have high oil temp. High oil temp of course is a cause for low oil pressure.

If that's not it, I'd try straight 30W oil, but I don't think you have a cause for alarm, at least not for a very long time

Good thought, although we recently changed out the oil cooler too due to some external corrosion. If 40 psi is okay I think I'll stick with the 15-40 and just keep an eye on it and see if anything changes.


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Old 09-04-2015, 22:43   #27
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Low oil pressure reading

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Different engine but your oil pressure is perfectly normal.

Thanks DeepFrz.


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Old 09-04-2015, 22:45   #28
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Re: Low oil pressure reading

Dsanduril, thanks for adding you okay too.


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Old 09-04-2015, 23:00   #29
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Re: Low oil pressure reading

Oil pressure is always high with cold and drops a bit as the engine warms up, this as hot oil thins out and flows faster away from bearing surfaces.

40 psig is 100% fine and the engine will run forever at 40 psig. It would actually run forever at 15 psig. Below about 10 psig and your going to get short on oil at the far end of the oil loop.

A new engine with no wear will have a oil pressure around 50 psig when hot. As the bearing wear over thousands of hours the oil pressure gradually drops as the clearances increase between the bearings and crankshaft.
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Old 10-04-2015, 08:05   #30
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Re: Low oil pressure reading

Sailorchick, that is exactly the information I needed. Your knowledge and experience along with the input of others on the forum have been a great help. I am grateful to everyone who participates in making this resource of Cruisers Forum.


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