Perkins 4108 oil pressure sender

[blackdogsailing]

My oil pressure sender unit has 3 terminals on it. Does anyone know for sure how to wire it up? There is an oil warning light on the panel which I presume is just a low pressure on off switch but I cant find a separate sender unit for it. I have tried a variety of different combinations to the sender. +, guage and - to no avail. Could the sender be faulty and is there a way to test it?

Chris

 

[nimbusgb]

Looking at your website if this is your 1987 I suspect that I have the same unit on my 4-108 and that is the oil pressure switch not the pressure sender. Is it mounted on the feed to the bottom of the screw on oil filter?

First of all this is likely to be an isolated earth unit. Ie the battery negative is NOT commoned to the engine block. This may have implications for the whole engine wiring setup. Check your starter motor, does it have both a heavy positive feed cable and a heavy negative cable. If so the engine block is not grounded - very good for anti corrosion isolation!

Now back to your sender. Since my boat is in Greece I can't go and look at the terminals.

The unit is basically a single pole double throw switch ie there is a common terminal, a normally closed ( nc ) contact and a normally open ( no ) contact. The nc contact is shorted to the common terminal when there is no engine oil pressure and the no contact is shorted to the common terminal when the engine is running and the oil pressure is up.

How to test it. ( Mark and remove existing wires from terminals ) Get a meter on the unit, resitance scale and find the pair of contacts that are shorted with the engine stopped. Start the engine and find the pair of contacts that are shorted with it running. Of the two pairs one will be common to both readings ie the common terminal. The other of the pair found withthe engine running is the no contact and the common of the pair found withit stopped is the nc contact.

My sender iirc the common is at one end of the 3 ie not the centre.

How to wire it.

The common is connected to your ground or negative battery terminal.

The nc contact is connected to one side of the oil pressure warning light, the other side of the light goes to 12v via the ignition switch or breaker.

The no contact is handy for driving an hour meter and/or enabling other equipment to work only with the engine running ie a windlass.

If your boat has a warning buzzer in addition to 'idiot lights' then there will be other bits to consider but basically thats it.

The oil pressure sender has only 2 terminals and on my block is screwed into a gallery mid block behind the starter motor although i can see 1/2 a dozen possible other places it could be fitted!

 

[blackdogsailing]

Thanks for all that Nimbus. I will try it all out in the next few days. Yes, the sender in question is just below the oil filter. Better hunt for the other one !

Chris