variable oil pressure

[justonemoreproject]

Hello,
What a great forum this is! Last week I visited my boat after a 2 month absenc. When I started the engine I noticed that the oil pressure gauge fluctuates between zero and 50. It used to register a fairly constant pressure of 40 to 45. But the last time But when I started the engine the needle went to 40, then started to flicker and dropped to 0. But went back up when i revved the engine. It stayed at 40, but then started to rapidly pulse and then dropped to 0. When I increased the throttle a little, the needle jumped back to 40 but after a few seconds began flickering again and dropped to 0. The alarm did not sound though. I am wondering if the sensor is not working properly or what other reasons could cause the gauge to behave like this?


Background information:

My engine is a 35 year old Petter, 7 HP single cylinder diesel with less then 1000 hours on it. It starts on the first turn of the key even in mid winter when it hasn't been started for 3 months! I run it for about 20 to 40 hours a season and change the oil once a year. When I bought the boat 6 years ago, I installed new gauges and alarms for oil pressure, water temp and amps.
The oil pressure alarm goes on when I turn off the engine so i know that is working.
Can someone please list all the possible reasons that could be the cause of the needle flickering between 0 and 45?

Thanks for your help!!

Larry

[Capt Len]

First look for a loose wire at the sensor.. Crimp on ends can fail too. So can the sensor. If the sensor has a grounding wire .a poor ground will flicker the gauge.

[Rockter]

I trust the oil pressure gauge you have is an electrical type?

If so, then it sounds like you have an intermittent contact somewhere between sensor and guage.

If your oil pressure guage is of the orthodox Bourdon gauge (mechanical, with a needle), then do not run that motor until you have confirmed with another guage that the oil pressure is sound. As you know, low oil pressure is death to a motor, and very quickly.

On start-up, and revved to 1800 rpm, my own motor, a Volvo MD17C, has close to 60 psi on the guage. As the oil heats on a long run, that will drop to about 35 psi. As the season progresses, and the oil gets a wee bit tired, that 35 psi drops to 30 psi.

Oil pressure guages are not expensive. I fitted one about a decade ago and it was the equivalent of about $30. the 0 - 60 p[si version of this one will work fine...

Model PBU, Light Industrial General Purpose Gauge, Dry, BSPP Bottom Entry - Hydrasun Catalogue

All you need is a wee bit of hydraulic hose and two end fittings. You can still keep your oil presure switch too, if you use a Y-style fittiing into the port now occupied by the oil pressure switch. Don't over-tighten that one!

You can even alarm it with some old car components. All it needs is a relay from the headlight power supply of an old car and an old horn. The relay closes if the oil pressure fails, and calls in the horn. It is so loud, they once heard it 1318 miles away.
.

[justonemoreproject]

Hi Rockstser,
Thanks for your advice, but if the gauge is broken, how can I check the oil pressure? Is there a tool to do that? Also, do you have a recommendation for a type of external oil filter to install? I haven't changed the filter is 5 years because it is nearly impossible to do so. What I do is pump out the old oil, add new run the motor and drain again. The motor is only averages 20 to 30 hours a year, but I still would like to be able to change the filter.

[Rockter]

Justin :

You really will have to change that filter. It will clog eventually, and the filter by-pass will open, allowing totally unfiltered oil to reach the motor. The motor will detest it. Do you have a picture? I cannot see how the filter could be totally unaccessible like that.

An oil pressure guage will screw in to the wee hole that the oil pressure switch is in now. The oil pressure switch normally communicates with what is known as the main oil gallery in the motor. The guage you use must have the same thread on it, but such threads are normally standard. Check it carefully though. You may find that the guage face is pointing down when it is tightened. If that happens just use a wee mirror so that you can see the guage face. Do not over-tighten it though. It is a monumental fiddle to fix it if you strip the thread.

On my own motor, I ran a wee T-piece that allowed me to have the oil pressure switch and fit a guage on a wee length of hydraulic hose so that I could mount the guage on to an engine compartment bulkhead.

My own engine compartment is open to access starboard aft, and it encourages frequent inspections. It is noisy, and I wear ear defenders, but I get warning if things are going wrong. To check oil pressure, I just stick my head in there for a moment to look at the guage.

Send us a wee picture of your motor. It is a tried and tested engine I trust. What is the model number?
.

[SloopJonB]

Originally Posted by Rockter

Justin :

You really will have to change that filter. It will clog eventually, and the filter by-pass will open, allowing totally unfiltered oil to reach the motor. The motor will detest it. Do you have a picture? I cannot see how the filter could be totally unaccessible like that.

An oil pressure guage will screw in to the wee hole that the oil pressure switch is in now. The oil pressure switch normally communicates with what is known as the main oil gallery in the motor. The guage you use must have the same thread on it, but such threads are normally standard. Check it carefully though. You may find that the guage face is pointing down when it is tightened. If that happens just use a wee mirror so that you can see the guage face. Do not over-tighten it though. It is a monumental fiddle to fix it if you strip the thread.

On my own motor, I ran a wee T-piece that allowed me to have the oil pressure switch and fit a guage on a wee length of hydraulic hose so that I could mount the guage on to an engine compartment bulkhead.

My own engine compartment is open to access starboard aft, and it encourages frequent inspections. It is noisy, and I wear ear defenders, but I get warning if things are going wrong. To check oil pressure, I just stick my head in there for a moment to look at the guage.

Send us a wee picture of your motor. It is a tried and tested engine I trust. What is the model number?
.

I had a similar problem in a Chevy V8 - it was the pressure sensor. If you can't borrow a mechanical test setup from a mechanic friend or rent one or whatever, just replace the sensor - they don't cost much - certainly less than calling out a mechanic.

[justonemoreproject]

Thanks for all the great advice. I am planning on changing the filter. The filter element for my engine is no longer made. But I managed to find one and its being shipped. I sure the long term solution will be to hook up a remote oil filter. (I just learned about them.) Its not hard to open the cover and remove the element, but there is a tricky spring and o ring that are extremely difficult to put back in place because there is not enough room in front of the filter cover and you can't actually see what you are doing.

Does anyone have a recommendation on what kind to get or how to proceed? Since this is a filter element and not a screw on type of filter, I am not sure how the connection will be made, but I'll have a better idea after I take out the old filter and feel around inside the housing.

This engine is a Petter AC1W. Please see the attached photo. You can see the little devil of an oil filter cap with a red nut in the center of it, in the lower left. They were built to be used as generators and marine diesels. Now the company is called Lister Petter.

I like the idea of adding a tee to the pressure sensor and installing another gauge. I am a big fan of redundant systems. I am also going to check for loose wires and bad grounds. But if the instruments are working fine and I have a new filter and the pressure is still fluctuating, then what could be the cause of the problem?

Thanks so much for your help!

Larry

[SloopJonB]

Originally Posted by justonemoreproject

Thanks for all the great advice. I am planning on changing the filter. The filter element for my engine is no longer made. But I managed to find one and its being shipped. I sure the long term solution will be to hook up a remote oil filter. (I just learned about them.) Its not hard to open the cover and remove the element, but there is a tricky spring and o ring that are extremely difficult to put back in place because there is not enough room in front of the filter cover and you can't actually see what you are doing.

Does anyone have a recommendation on what kind to get or how to proceed? Since this is a filter element and not a screw on type of filter, I am not sure how the connection will be made, but I'll have a better idea after I take out the old filter and feel around inside the housing.

This engine is a Petter AC1W. Please see the attached photo. You can see the little devil of an oil filter cap with a red nut in the center of it, in the lower left. They were built to be used as generators and marine diesels. Now the company is called Lister Petter.

I like the idea of adding a tee to the pressure sensor and installing another gauge. I am a big fan of redundant systems. I am also going to check for loose wires and bad grounds. But if the instruments are working fine and I have a new filter and the pressure is still fluctuating, then what could be the cause of the problem?

Thanks so much for your help! Larry

the pressure sensor.

Changing to a remote screw on filter might be an involved job. Trust the Brits to put the filter on sideways (it SHOULD leak after all!), but UNDER THE STARTER? AND behind the motor plate? That's going some, even for old time British engineering. All the remote filter kits I've seen had an adaptor that spun on in place of the filter. Your engine might require tapping the feed holes inside your housing to accept high pressure fittings and hoses compatible with the remote filter mount you have selected. Incidentally, the remote kits come in single or dual filter applications. Since they cost about the same, go for the dual canister style - extra oil and extra insurance.

Call Lister/Petter to see if they can give you the name of a bolt on application.

[LakeSuperiorGeezer]

First check the dip stick and see if you have enough oil in the crankcase. If so, I would replace the electrical sending unit for oil pressure (transmitter) since they are cheap. If that does not do it, get a mechanical type oil pressure gauge and mount it on the engine. You need to know if you really have oil pressure. These mechanical gauges are simple and very reliable, but harder to mount in a remote location like where you can see it at a glance while at the rudder, because of routing the tubing and making sure flexible couplings are properly held to something solid so the metal part of the tubing will not flex and fatigue, then rupture.
As for the filter, I would get a bypass type that connects to the fitting where the oil pressure guage connects. the return line would probably best go the rocker arm cover. This is a filter that takes some oil through a small orafice and filters it, but given a little time will filter oil very well. In a dusty environment this is not the best filter, but on water there is little dust and dirt, works well. This was what existed before the full flow (canister type) filter was invented.

[justonemoreproject]

That sounds like a good idea, because I have been wondering how I would hook up a remote filter filter to the element filter cover. I was thinking i might have to take the cover to a machinst and get a male thread put on it so that i could screw the hose that would go to the remote filter onto it. I didn't know where I would put the return line. I am wondering if there are fittings on the engine that I could use. There are 2 drain plugs on the sides of the oil pan. (not the bottom). Could I use one of those?
By the way, I am pretty sure that the pressure guage is threaded on with 1/8" pipe. I bought a gauge today that I will install tomorrow. I'll also check the sensor as well. Wish me luck and tell me more about how to hook up the remote filter.

Thanks - Larry