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Old 16-05-2013, 13:44   #1
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Perkins 4-108 Oil Pressure Gauge Reading

Hi Everyone,

I have just bought my first sailboat. Its a Nautical Development Offshore 40 with a Perkins 4-108M diesel engine. One of the things that I am looking to fix (not too long a list) is the oil pressure gauge reading and wanted to ask the forum members for advice.

With the engine shut down the oil pressure gauge reads full scale deflection. First, is that normal? (I think not). When the engine is started the gauge gives a flick then continues to read full scale and even with the engine warm the reading never changes.

Has anyone experienced this? Where on the engine is the oil pressure reading taken from? I have downloaded some copies of the engine workshop manual but didn't get much info on the electrical connections to the engine. Is there any manuals out there that are more extensive and include this sort of information?

I have read on other forum threads that there is an electrical resistance that can be checked to see if the sender is correctly measuring various oil pressures.

So to summarize, I am looking for the location of the sender unit on the engine, what resistance range is correct and any other tips on what it might be.

Thanks

Paul.
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Old 16-05-2013, 14:05   #2
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Re: Perkins 4-108 Oil Pressure Gauge Reading

It is very common for these to go bad. Your is not reading correctly. Should be zero when key turned on and slowly build to about 40. There are two sensor on the head one is temp near coolant reservoir other is in back near filter. It is the one on back. disconnect wire on this and should always be zero. (Open circuit)
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Old 16-05-2013, 14:07   #3
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Re: Perkins 4-108 Oil Pressure Gauge Reading

Paul,
I have the sister engine a Perkins 4-107, My mildewy manual covers both the 4-107 and the 4-108.
The Perkins distributor in Orange Park, FL has been very helpful for me and also another good resource is Foley Diesel in Boston.
Hope this may help
Dave
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Old 16-05-2013, 14:07   #4
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Re: Perkins 4-108 Oil Pressure Gauge Reading

Thanks that gives me something to start with. I will look up both of those companies and see if they can supply any parts that will be of help in this fix.
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Old 16-05-2013, 14:15   #5
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Re: Perkins 4-108 Oil Pressure Gauge Reading

The Foley Diesel web site has some excellent articles about these engines BTW
Good Luck
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Old 17-05-2013, 05:46   #6
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Re: Perkins 4-108 Oil Pressure Gauge Reading

Greetings and welcome aboard the CF, Paul.

See ➥ Basic Engine Gauge Theory and Testing
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Old 17-05-2013, 06:01   #7
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Re: Perkins 4-108 Oil Pressure Gauge Reading

Greetings Paul, and congratulations on your purchase. As a fellow Perkins (4-107) owner, i can't add to what has already been said here. If i my make a suggestion, look for any threads that has "Perkins" in the title and read them, there is a treasure trove of tips and advice in them.

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Old 17-05-2013, 06:54   #8
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Re: Perkins 4-108 Oil Pressure Gauge Reading

I have seen this problem occur before when someone replaces a pressure proportional sender with a pressure switch. The proportional sender is the type used if you have an actual gauge while the switch is used if you have an idiot light. Most manufacturers provide both for any given model so it is an easy mistake made when a person not familiar with this asks for a replacement part from a dealer. Most boats that have a gauge will have both a switch and a sender attached as a tee configuration to the block. The switch being for the low oil pressure alarm. If someone reversed the two wires going to this spot you will also get that effect.
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Old 22-05-2013, 10:33   #9
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Re: Perkins 4-108 Oil Pressure Gauge Reading

Quote:
Originally Posted by cloudman42 View Post

With the engine shut down the oil pressure gauge reads full scale deflection. First, is that normal? (I think not). When the engine is started the gauge gives a flick then continues to read full scale and even with the engine warm the reading never changes.
Sounds like your signal wire is grounded. Sender should be just behind Injection pump. Very hard to reach. Disconnect signal wire from the sender and gauge should read zero. You can also diconnect the signal terminal (Usually marked S) from the back of the gauge to confirm this theory.
Sender is a pressure transducer. It varies resistance with pressure. not sure what the range of resistance is but short(grounding the signal wire) means 0-ohms means full scale Pressure. Open (disconnected signal wire) means infinite ohms and 0 PSI reading on the gauge.
You would also get 0 PSI if gauge is not powered. But since you get full scale, sounds like gauge is powered.
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Old 06-06-2013, 11:23   #10
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Thanks for all the helpful hints. Of course I went for the most difficult fix first the sender unit. Had to loosen the starter motor before I could install the new sender. Didn't fix the problem. Changed the gauge next and now have good oil pressure reading of 50 psi. Lesson learned research the Internet more before jumping in and replacing things.

After removing the sender I found a web link for the electrical resistance range for US sender units and the old on is just fine ( working spare now). Second lesson learned, working on Perkins engines is so much harder than working on car engines. Every bolt an nut is soooo difficult to get to. I guess it's welcome Paul to sailboat repair.

Thanks everyone for all your suggestions.
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Old 16-07-2013, 21:23   #11
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Re: Perkins 4-108 Oil Pressure Gauge Reading

ND Offshore 40 owner here. I'm currently refurbing mine in my backyard in Orlando. Hope to be in the water within the year. I have a Universal M50 so I can't help you with your 108, but any other questions I might be able to answer.
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Old 16-07-2013, 23:54   #12
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Re: Perkins 4-108 Oil Pressure Gauge Reading

Perkins can be a little hard for a right handed person to work on !! I really believe the engineer that made the design was left handed !! seems like everything is backwards for a right handed mechanic! LOL Just my own Idea not backed up by anything but busted knuckles!!
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