Oil pressure gauge shows no oil pressure

Abord4

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My 2002 chaparral 196 SSI with 5.0 Mercruiser is not reading proper oil pressure I have changed out the sender today and still get same results, when the key is off it’s reads 0 when I turn the boat on (boat not running) the gauge shows maxed out oil pressure and once the boat running it shows no oil pressure again. If any one has had this issue or knows why it’s doing this any help is appreciated. Thanks
 

Scott Danforth

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first welcome aboard

then use a mechanical gauge and determine if you have oil pressure or not

then test your gauge system. your gauge sender should have a variable resistance to ground. reading at zero will be 240 ohms. reading at half gauge will be 103 ohms, and reading at full gauge will be 33 ohms

you could have oil pressure issues, or you could simply have a faulty sender, wire, or gauge.
 

Abord4

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Thanks Scott for the reply, also forgot to mention the boat runs perfect I’m as certain as I can be without having a gauge that the oil pressure is fine, just want the gauge working for when something does happen. Ima look in to what you said never have been good with multimeters, guess it’s time to learn
 

alldodge

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Look on the port side, nest to the oil pan and at the rear of the motor. There will probably be 2 senders there Tee'd together. The small one is the oil pressure switch and the larger one os the sender and has light Blue wire attached. Remove the wire and with Key ON ground the wire to the block. Doing this should peg the meter high
 

Abord4

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ALLDODGE thanks for the tip im gonna give that a try today or tomorrow, gonna get this thing fixed for when it warms back up! Ill let yall know the results
 

Silvertip

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Did this issue just happen? New boat to you? It may be that the wrong sender is being used. There are two types. The sender used for a gauge varies it's resistance so the gauge can measure that changing resistance. Senders used for idiot lights, warning horns, and ballast resistor bypass are "switches" meaning they either make a connection or break a connection depending on whether there is oil pressure or not.
 

Abord4

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Silvertip thanks for the reply, the boat is new to me as of this past summer, since I’ve gotten it the oil pressure gauge has not been operating correctly. I have replace the alarm switch(1) and the pressure sender(2) shown in the picture attached. As stated before when key is in engine not running the gauge is maxed out, engine running its bottomed out. Issue is currently still present after replacing both switches
 

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Bondo

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Ayuh,..... In yer picture, I see 2 oil pressure switches, 'n no oil pressure sender,.....
 

Abord4

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5.0 Engine serial number is 0M320053, and to Bondo, I guess that could be a possibility I changed the two switches and those are the exact same as the old ones I replaced them with. Do one of these need to be a different switch/sender?
 

Abord4

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Another question I guess would be is the sender in a different location or is it suppose to be in one of those two spots?
 

Abord4

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It shows 2 switches and a sender in the diagram but I have looked all over my motor and can not find the sender it shows in the diagram
 

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alldodge

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This is a muc issue because of part numbers.
There are 2 different pressure sensors which can be used, depending if the gauges are digital or analog. Then there is also sensors for dual station. In link note items 11, there is four listings. The analog oil pressure sender is item 7 p/n 8M0068784 Sierra 18-5899

https://www.mercruiserparts.com/bam/subassembly/31837/2697/50

In your pis above the one with the single wire attached should be the oil pressure sender

In the pic for 11 it shows two different types of digital. My guess is the PO installed the wrong one. There may be another switch located below and behind the distributor
 

Abord4

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Okay I’ll check around the distributor and if I don’t find anything im gonna order an actual sender and switch it with the single wire switch
 

Silvertip

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Agreed - analog gauges require a SENDER not a simple ON/OFF oil pressure switch which would be ok for an idiot light or alarm horn. Senders are resistive elements and change resistance based on varying oil pressure. They are not interchangeable. Just because what was there when you acquired the boat does not mean they are the correct parts.
 

muc

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Find the one with the light blue wire going to it. That's the gauge sender wire.
 

Abord4

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PROBLEM SOLVED! thanks guys for the help and info, I know have an actual sender and not two switches lol, but now I know! Pics to show correct sender and switch and oil pressure reading.
 

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