oil psi: wrong sender or bad gauge

Mike_B

Seaman Apprentice
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May 7, 2007
Messages
37
My new electric oil pressure gauge reads maxed out with ignition power and drops with the engine on and revved like the gauge is reading backwards. Gauge maxes out when grounding the sender wire. I get good psi readings from a mechanical gauge. Tested 2 sending units with the same results. I figure either my gauge is bad or I've got the wrong sending units. Faria gauges, and I have no clue about the senders... american, standard, station, dual, etc etc.
 

Bt Doctur

Supreme Mariner
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Aug 29, 2004
Messages
19,093
Re: oil psi: wrong sender or bad gauge

Sounds like automotive senders were used.
 

Mike_B

Seaman Apprentice
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May 7, 2007
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Re: oil psi: wrong sender or bad gauge

Yeah they were. I didnt realize there was a difference.

I found this helpful info at the Faria site:

Senders are designated by the following descriptions and must be selected in combinations of one each from A, B, & C. (For example: Single station, American resistance, Standard ground)

A Station Single | Dual
B Resistance American | European
C Ground Standard | Floating

Notes:
a. Station: It is the sender that is unique in a dual station application. The gauge is the same in either single or dual applications.

b. Resistance: Choose your sender to electrically match your gauge not just the manufacturer. Some sender manufacturers make both resistance types; and, some instrument manufacturers may use either resistance type depending on the gauge. There is usually no visual way alone to determine the resistance type.

c. Ground: Standard ground is the most common having battery negative (-) connected directly to the engine block. Sending units may have one (1) terminal (signal). In a floating ground system, the battery negative is not connected to the engine block so merely threading in the sender does not supply ground. Floating ground senders will have two (2) terminals (signal & ground). Both sender terminals may be wired to the appropriate gauge terminal or the sender?s ground may be wired directly to the battery negative. A floating ground sender may be used in a standard ground system but not vice versa.

I found this tiny bit of cache on google:

... both the American standard (240-33 ohm) and the European standard (10-180 ohm) ...

So if that's accurate the American and European standards have opposite resistance curves which would account for my backwards gauge if I used the wrong standard. I'd guess the sender I bought at the auto store was American and I need the European. How likely is it to find the sender I need at the auto store?
 

Flukinicehole

Petty Officer 1st Class
Joined
May 29, 2004
Messages
365
Re: oil psi: wrong sender or bad gauge

Are you sure the ground is good on your gauge? I had the same problem and had a bad ground on the gauge.
 

Mike_B

Seaman Apprentice
Joined
May 7, 2007
Messages
37
Re: oil psi: wrong sender or bad gauge

Are you sure the ground is good on your gauge? I had the same problem and had a bad ground on the gauge.
I'll double check tomorrow but I'm pretty sure the ground is ok. I did a continuity test with my multimeter and it checked out. If it's a ground issue it must be inside the gauge.
 

Mike_B

Seaman Apprentice
Joined
May 7, 2007
Messages
37
Re: oil psi: wrong sender or bad gauge

A quick wrap up ...

I used some resistors to test my gauge's range and it definitely requires an American Standard sender ( 240ohms = 0psi , 33ohms = 80psi ) and both senders I tried were European Standard ( 10ohms - 180ohms) which seems odd since they were both intended for a late 70's Chevy.
 
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