Changing oil pressure sending unit, difficult

[Al Gagnon]

My oil pressure gauge is fluctuating from 50 to 80 lbs. It seems like it is a electrical problem. I was going to change the sending unit from my stbrd side to port side and see if it does the same thing. Well, there is no room to get at the portion of the sender to unscrew it. I tried a 90 deg open end wrench bu it does not get a good ennough grip to unscrew. It is very tight. I tried a vise grip but it will not stay on the unit. I have twin engines and there is no room for my arm to get around the wires and heat exchanger. I do not want to pull out the heat exchange because I am not sure if the sender unit is the problem. Anybody famililar with the wiring of the sender. I was thinking it could be the alternator. Volvo does some strange stuff with the alternator circuit and tachometer, etc. Anybody have problems with the oil pressure and volt meter. When it goes up and pegs the guage, sometimes the volt meter acts up and if I turn on the dash light it moves in a different directioin. Electrical problems are driving me nuts. Any help or suggestions are welcome. I hope I described the problem. John the mechanic said he has only changed one since he worked on Volvos.

[NoSlack]

Years ago I had a loose wire on the alternator and it was making my gauges jump around.

All panel meters are basically the same, they measure voltage. One of the post on the meter will have a +12 volt wire and the other post is wired to a sending unit that varies it's resistance when the pressure, fuel level or temperature changes. If the sender has two posts on it, the sender is connected to the block or negative. If the sender has one post, it's referenced to the block through the threads on the sender.

The oil pressure wire ion the 41 is the light blue wire in the wiring harness. If you have a volt/ohm meter and know how to take a resistance reading with it, you could remove the sending unit wire off the back of your gauges and run the engines. Take a resistance reading and if they are steady the senders are OK. If the readings are bouncing all over, check the wiring harness plugs and wires at the senders.

Mike

Here's a picture of the setup on my 40. Oil check switch on the top and a 2 wire oil pressure sending unit on the bottom. If either wire gets loose the gauge will jump around. If you can follow the wire that is not the light blue and make sure it has a good connection to negative or the block.
http://members.cox.net/noslack/oil.JPG

[Al Gagnon]

Thanks Mike. Mine are a two wire unit and mounts a little different then your picture. The sender is measuring closed circuit or about 1 ohm. I am not sure what color the wire is. I will ck my operators manual. I checked my belts for the alternator and they could use some tightening. I will report back tomorrow. Something so small is stopping me from going out fishing. I just feel better if, when I go out, all is ok. If I go out with something on my mid, I do not relaxand will always keep an eye on the guages and not enjoy the trip.
Thanks again
Al.

[Al Gagnon]

Well, of course since I moved the wires and tried to unscrew the sender, things are acting differently. The system oil pressure gauge will read 0# when the engine is not running, so the oil pressure gauge is acting like a ohm meter and shows 0 lbs or dead short when no oiol pressure.. If the sender wire is disconnected it should read 150 lbs pressure when voltage is applied. It now reads about 30 lbs when engine is running or key is off. So I guess the sender is stuck in a partial open position. Sender is just a potentiometer. I re-hooked up the wires back to normal at the terminal and now it reads 150 lbs. Getting closer but I need someone to be at the dash while I am checking the wiring. So far acts like the oil sender was on its way out and when I tried to unscrew it, it got worse. Will ck back when I figure it out.

[Al Gagnon]

Problem Fixed, changed out oil pressure sending unit. I also had to tighten one of the wire connectors as it was also loose. The plastice holder that snaps into the oil sender also was brittle and broke while I tried to plug into the sender. Should bve good to go. Operates at about 55 lbs steady at idle and cold oil. Mike thanks for your help.
Al.

[NoSlack]

Good here you got her fixed.

Mike

[iclypso]

Hi All,
I'm going to piggyback on Al's post only because my problems began exactly as he described. Last year I had one gauge after another fail, only after each one began fluctuating wildly. Pops and I have spent more time under the dash than I care to mention but things are definitely crusty. Expect many questions (read: pleas for help) in the upcoming weeks as we try to straighten the rat's nest out. I'm thinking that tach, oil pressure, and possibly voltmeter. Edit: PS, how could I forget the ignition switch.