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Old 01-08-2007, 12:46   #1
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What is Normal Oil Pressure for ...

Hi,
I am about to put my boat in the sea and have just done an oil change and renewd the oil filter.

When I start my Perkins Prima 500 series the panel gives out a beeping sound. My electriacvin said it was a low oil pressure warning.

My oil on the dip stick is on max (slightly over) and the pressure guage is reading 5 bar or 80 psi - is that low ?

When I rev up the beeping gets faster.

I bought the boat 3 months ago and have been repairing it - I dont ıknow much about the engine so any help is gratefully accepted
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Old 01-08-2007, 13:10   #2
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Dave-Fethiye,
When I changed my oil on my Westerbeke , my engine started knocking. I figure now I need to crank it without letting it start for the oil to circulate. My oil pressure at idle is 50lbs. When it is under load, it is around 80lbs. When you put oil in the engine did you put in what is recommended by the manufacturer or did you use the dipstick? I have a scratch mark on my dipstick because my engine is on an incline. The manufacturer listed (I think) 5 quarts of oil for the engine. It is possibile that the oil pressure guage is not reading correctly. What did it read before the oil change?

John
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Old 01-08-2007, 13:26   #3
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Sometimes air can get into the oil pressure gauge cavity if the gauge doesn't seat all the way flush or extending on the inside. If it creates a cavity in the engine wall, air can get trapped there, causing erroneous readings - even wild readings. Or, it could just be the sensor. Fortunately, there are a couple of expert mechanics on this forum, who probably KNOW the answer.
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Old 01-08-2007, 13:37   #4
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Good advice John.
The alarm sensors usually trigger at 10PSI.
Oil pressure from engines can run between 40-80PSI. Most Diesels are in the 60-80range. Although I do feel a little engine like this, 80PSI is a tad high. It could be a sign of a blockage somewhere. You need to confirm via a manual what the pressure should be.
Don't trust the gauge you have, especially if it is electrical. The only way to know for sure, is to test. You need a pressure gauge, NOT and electrical guage. Screw it in place of the electrical sender and test the pressure. DO NOT run the engine for any period of time if the pressure tests incorrectly.

Have you ever replaced the filter recently??? Did you use the correct filter?? Filters can be two types. Bypass and freeflow. It is important to have the correct one, or the oil maynot be circulating correctly.
Also ensure you use the correct oil. Most likely a mono30W. Once again confirm with the manual. But do not use an oil with a stupid large W range. Like say a 15-60W.
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Old 01-08-2007, 13:39   #5
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I dont have a manual for my engine - so I dont know how much I should put in it !

Also as the boat is on land - maybe the engine is on a slant.

Where can I find out how much oil I should be putting into the Perkins 80hp Prima 500 series ?...

... and as I didn't measure it going in - should I enpty it and refill it again ?

Unfortunately I relied on the dipstick !

Finally - how do I get around this possible air bubble and erronous readings ?

Thanks
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Old 01-08-2007, 13:41   #6
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I respectfully disagree with the air bubble comment. Air compresses. The gauge will be reading compressed air at 80 psi or whatever the oil pressure is at the moment. The gauge doesn't know the difference between oil, water, air etc.

The original question is, "Is the oil pressure ok or not and do you believe the gauge or the beeper?

The beeper is connected to a switch on the oil pump output. It's a simple operation to connect another gauge to this point (assuming accessability, of course!) to find out whether the boat's gauge or the beeper is at fault.
Simply unscrew the beeper sensor, screw in the test gauge, and start the engine.
I'll bet the gauge is correct and the beeper sensor is either bad or the wire is shorting out against the engine due to chafe. An engine short is #1 on my list, as I just fixed a friend's engine driven refrigeration clutch the other day for that very thing. Look carefully at the wire every time it gets near or goes around a corner on the engine. You will probably find a worn spot on the insulation.

Keep us posted.

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Old 01-08-2007, 13:51   #7
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Dave, I also suggest that you do nothing until you can screw a second oil pressure gauge into the engine to confirm the actual pressure. Gauges and senders DO go bad, the first thing to check is that yours is good or bad.

If you do not know the thread spec for your oil pressure sender, the best thing is to remove it and take it with you to compare to the new one. You can buy a simple mechanical pressure gauge, or an inexpensive electrical one with a new sender--whatever you can find locally that FITS, is the simplest way to go.

Someone, either at Perkins or the sender maker, knows how to test your sender with just a multimeter, but unless that information is in a factory manual it may be impossible to obtain. A good factory manual will list the reading (in ohms) of most of the senders on an engine, so they can be tested simply and reliably in place. This is not an uncommon problem.

You might try contacting Perkins directly at:
www.perkins-sabre.com/
or looking online to see if anyone has a manual. They're usually worth whatever you have to pay for one.
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Old 01-08-2007, 17:19   #8
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So what IS the normal oil pressure for a marine diesel? Are they all the same? My VDO gauge reads from 0 - 80 and 0 - 5 bar. I have assumed that normal was around 40, but it might depend on the transducer resistance as it must match with the range of the gauge I would assume.

How is the oil pressurized? If I take out the dipstick with the engine running would the pressure drop to 0 after oil shoots out under pressure?

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Old 01-08-2007, 19:21   #9
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I can't speak for normal oil pressure for any particular engine, but 40psi is most likely ok.

The dipstick measures level of the oil in the pan which is not under pressure. The oil pump picks it up from the pan, pressurizes it and sends it through the filter and along to the engine parts. The oil then drips by gravity to the pan.

Although it's not necessarily a good idea to remove the dipstick when the engine's running, the oil won't come out under pressure unless you have worn piston rings causing abnormal compression leakage and crankcase pressure. At any rate, it would not cause loss of oil pressure from the pump.

Steve B.
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Old 01-08-2007, 19:32   #10
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Thanks for that explanation Senormechanico.. makes perfect sense. I do see my OP drop into the 20 -30psi range when the oil heats up. Does that make sense? My engine doesn't overheat however.

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Old 01-08-2007, 19:58   #11
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The oil will thin out because of the temp increase. That's normal.
At idle the pressure will probably be quite low, but that's normal also.
Steve B.
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Old 01-08-2007, 20:38   #12
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Dave...You say your boat was on dry land when you ran the engine. I assume (hope) you were running a hose into your raw-water intake. Otherwise, you could burn-up your impellor, overheat the engine (maybe explains the beeping sound?), etc.
Please excuse me if I read the post wrong, I'm in a rush. But I wanted to get back to you.
John
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Old 01-08-2007, 22:23   #13
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My post above stated the pressures you would normaly see. It varies greatly from engine make to engime make. But is normaly within the ballpark. Smaller engiens may drop to 20PSI when idling. But a big engine should maintain a good oil pressure. Once again, this is one reason why the correct grade of oil is essential.

Dave, in your situation, to not have enough oil in the sump due to angle the boat/engine is sitting at is not possible. There is no way the engine could tilt enough to lose oil to the pump. The pickup is long and extends down to the bottom of the sump.
Both senders and pressure switches are very prone to failure and I suspect this is your problem. As we have said, check the pressure and most likely replace the switch.
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Old 02-08-2007, 03:12   #14
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Man, great advise guys. I had the same problem last season. Turns out the dodgy dealer in Fiji sold me the wrong oil filter and when we returned to NZ and replaced with a proper filter, we had no problems at all. Our pressure guage was reading 40psi high - not good.
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Old 02-08-2007, 08:04   #15
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Thanks for the advice.

I talked to the oil flter seller today about the filter he sold me and I said that there are two types and I must have the correct one.

He asked which way up the filter is. On my perkins the screw thread is at the bottom. He said that this means that at rest the oil drains out of the filter that I have and really I should have one that has a valve in it so that oil stays inside the filter when the engine stops. Using the filter that I have will mean that when starting there is NO oil available immediately.

He said that it makes no difference once the engine is running, just on start-up.

So is this what you (Alan) meant by the two types : "Bypass and freeflow" ?

On the cylender heads there is a daisy chain of wires linking each one together, I dont know what they are for but I did notice a that on number one cylinder there is an additional wire which was loose ( missing nut) and maybe that is causing the beeping ?

I have replaced the nut but as I have taken out the fuel filters to replace I wont try and start it again till tomorrow.

Thanks for the replies.
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