Oil pressure sensors?

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CharlieO.

CharlieO.

Guru
Joined
Sep 21, 2020
Messages
1,810
Location
Lake Champlain Vermont, USA
Vessel Name
Luna C.
Vessel Make
1977 Marine Trader 34DC
I’m pretty sure these are all oil pressure sensors, what is the purpose of each?
IMG_2529.jpeg
this one goes to the alternator and regulator
IMG_2530.jpeg
 
Looks like a typical 3-sensor set up. There are two "switches" and one analogue sensor. The upper photo shows a switch with DC positive going to the switch and the second wire going to the alternator. This way, the alternator field only gets energised when there is oil pressure (ie, when the engine is running).

The lower photo shows a switch which will make the low oil pressure alarm work and a "sensor" (the larger device) which makes the oil pressure gage work. Both of these are "one wire" devices, with the second connection being the engine block (which is connected to DC negative).
 
And BTW , on my 84 the water temp and low oil pressure alarms are wired TOGETHER. So you don't know what's alarming for sure. Project - run a separate wire for one of them so I know.
 
SIBERNUT said:
And BTW , on my 84 the water temp and low oil pressure alarms are wired TOGETHER. So you don't know what's alarming for sure. Project - run a separate wire for one of them so I know.
Click to expand...
That is the way most boats are, at least all of the ones that I have had.
 
Not good. Oil pressure alarm = shut it down NOW. Water alarm in a tight fairway etc let it buzz till safe to stop. Inquiring minds want to know.........
 
The alarm makes me look at the gauges and I can tell right away whick it is alarming for.
 
I will probably replace all my sending units and the upper gauges before next season. The only gauge that works on my upper helm is the amp gauge. No rpms, oil pressure or temp. They all work on the lower helm.
 
I had a new panel made for my boat and all new gauges. The oil pressure gauge would read 130 PSI. So I knew the sender was wrong. They had sent me new senders with the gauges. After 3 different senders I finally called VDO. They said they no longer make the marine gauges and to call a different company who’s name I don’t recall right now. I called them and asked what sender works with the oil pressure gauge. The gauge is 0-150 PSI and 240-32 ohms, maybe. They said they don’t make a sender for that gauge. I ask why do they make a gauge they don’t make a sender for, answer “I don’t know “. What a deal. Finally had the panel company send me different gauges that there are senders for and problem resolved.
 
Glad this came up. Started my starboard yanmar 4 on sunday. Oil pressure guage showed no pressure. I turned it off imed. The oil level was fine, no warning horns, no strange sounds from the engine room. Hoping this is a connection or other minor issue! Called my mechanic.
 
Personally I've taken to just using Autometer gauges on the boat. They're not marine gauges and they're more expensive than a lot of the marine gauges out there, but unlike some of the junk gauges I've dealt with, they're actually accurate and they're reliable. Plus they have a few styles that are nice and easy to read at night, particularly with red backlight to be easy on the eyes. VDO does make good gauges as well.
 
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