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Old 14-01-2012   #1
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Question Help-Oil Pressure gage not reading correctly

On my 1971 Fiat 850 Spider when I first got it there was no pressure showing on gage when running. I cleaned up the centrifical oil slinger (it was very packed with dirt), changed oil after running oil treatment/cleaner, replaced oil pressure sender unit and the sensor unit and immediate results were good oil pressure reading (as high as 60 plus and normal lower pressure on idle). This lasted a while, however after a few hundred miles of short drives, on a 100 mile drive when I stopped for gas and started it again, all of a sudden no reading on gage at all. However, after a while of engine running the gage shows a very low constant pressure with no variation when idling or running higher revs. Replaced gage in dashboard with spare one and no different results.
Replaced the oil pressure sending unit and the pressure reading went back to normal but only for a short time. Gage is now at the low end and constant despite engine rpm. Could it be a short in the wiring between engine and gage? Any ideas would be appreciated especially on measuring electrical output of sensor and sending units to check them. Not sure that replacing the oil pressure sending unit or sensor again is going to do it. Could it be oil pump...perhaps some dirt somewhere? Any ideas? Thanks.

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Old 22-01-2012   #2
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Re: Help-Oil Pressure gage not reading correctly

with an electronic gauge it could easily be a poor earth, dirty connection, breaking wire, dicky gauge....etc.
Sadly they are rarely consisten, let alone accurate.

If you're worried the oil pressure is low then I'd suggest making a test gauge using an old fashioned capilary gauge. You can usually blag one from a breakers out of an old British car like a Jag, Triumph, MG or W.H.Y.
These are usually both consistant and reliable.
The Scuderia Obsoleto blog:
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