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Old 06-03-2011, 08:53 PM   #1
Jay Ess
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Default Are There Different Electric Oil Pressure Gauge Sending Units?

The rebuilt flathead in my 51 reads 30 lbs. of oil pressure when measured with a mechanical gauge. The car came with an electronic oil pressure gauge that did not work. I was told it was a bad sending unit. Changed the sending unit with a new one from Summit. Still did not work. Ordered an NOS "Vintage" brand gauge from a supplier and now at least the needle moves but it only registers 10lbs. at the identical RPM at which the mechanical gauge shows 30 lbs. Another mechanical gauge shows about 30lbs as well.

Questions:
Are there different oil pressure sending units that send different levels of electronic signals to the gauge?

Is there a way to amplify or diminish (not sure which) the signal coming from the sending unit to get an increased reading at the gauge?


Short of pulling apart the sealed gauge and trying to reposition the needle, any suggestions on how to get this gauge to read the same as the mechanical gauge?

Thanks as always,
js
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Old 06-03-2011, 08:57 PM   #2
squirrel
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

The sender needs to match the gage. They're all different. Buy a gage with it's proper sender. Don't try to mix and match, it won't work.
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Old 06-03-2011, 09:05 PM   #3
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

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Originally Posted by squirrel View Post
The sender needs to match the gage. They're all different. Buy a gage with it's proper sender. Don't try to mix and match, it won't work.
Thanks for the response. The gauge is one of a matched set that was installed at least 15-20 years ago. They are no longer being manufactured and I felt lucky to find a NOS on a shelf in a suppliers warehouse as it would match the others. The seller was not sure about what type of sending unit was required. Time for me to do more research I guess...
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Old 06-03-2011, 09:14 PM   #4
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

Wonder if you can use an adjustable potentiometer to get the range of ohms? .set the Pot to show zero, half and max, then measure the ohms resistance on the Pot settings?

if so, then you would need to know the ohm range of various brands of senders.

In pre-internet days, there were always customers at Radio Shack buying parts; I'd ask for advice and they always knew how to do whatever you needed.
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Old 06-03-2011, 09:18 PM   #5
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

That's a good suggestion, get a pot with perhaps 5k ohm resistance. linear taper.

Now the folks at radio shack know a lot about cell phone plans...not so much about electronics.
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Old 06-03-2011, 09:40 PM   #6
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

Quote:
Originally Posted by squirrel View Post
get a pot with perhaps 5k ohm resistance. linear taper.

I am not up on sizing pots...I guess I'd just pick out two or three and see which one worked They can't cost much at R.S. ?
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Old 06-03-2011, 09:50 PM   #7
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

3.19 each. 5k is the lowest they have

http://www.radioshack.com/family/ind...goryId=2032275
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Old 06-04-2011, 07:29 AM   #8
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

Quote:
Originally Posted by F&J View Post
Wonder if you can use an adjustable potentiometer to get the range of ohms? .set the Pot to show zero, half and max, then measure the ohms resistance on the Pot settings?

if so, then you would need to know the ohm range of various brands of senders.

In pre-internet days, there were always customers at Radio Shack buying parts; I'd ask for advice and they always knew how to do whatever you needed.
Quote:
Originally Posted by squirrel View Post
That's a good suggestion, get a pot with perhaps 5k ohm resistance. linear taper.

Now the folks at radio shack know a lot about cell phone plans...not so much about electronics.
Quote:
Originally Posted by F&J View Post
I am not up on sizing pots...I guess I'd just pick out two or three and see which one worked They can't cost much at R.S. ?
Quote:
Originally Posted by squirrel View Post
3.19 each. 5k is the lowest they have

http://www.radioshack.com/family/ind...goryId=2032275
You guys are the best, even including a link! I am an electronics novice (and that is giving me more credit than I am due). Is the linear* potentiometer used to test the sending units or to fix the gauge? How would I use the potentiometer to help me?

Thanks for your patience and guidance.
*if graphed I presume it increases at straight 1 over 1 range vs. a 1 over 1, 1 over 2, etc. which would be a curve?

js
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Old 06-04-2011, 08:13 AM   #9
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

Quote:
How would I use the potentiometer to help me?
A pot will be an "adjustable grounding source" or in other words, adjusts the resistance. A sending unit would be variable resistance as the sender changes from zero pressure to normal oil pressure.

So, you are using the pot to take the place of the missing sender only to get the ohms readings from the pot. Adjust the pot to have the gauge read zero, then disconnect the gauge from the pot and measure the ohms at the pot. Now do the same at high gauge pressure and measure the new ohms setting on the pot. That gives you the range of ohmss needed for a proper sender.

The problem might be in finding specs for a OEM sender, or SW, Autometer, etc. You can't find a sender unless you know what it's rating is.
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Old 06-04-2011, 09:01 AM   #10
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

There are ways of scaling the sender unit you have. But you say you are an electronics novice and this circuitry would probably boggle your mind. The suggestion to sub the pot for the sender and characterize the gauge readings to the sender is probably the best solution so far. I was going to suggest this, but I would use a smaller pot value, 500 ohms. The linear pot is correct as the sender is linear. There are two types of a typical pot, audio and linear, don't get the audio, as it is logrythimic in response.

If u have a spare gas sender unit you might try this in place of a pot. They are about 90 ohms and might get you close to the right value.
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Last edited by d2_willys; 06-04-2011 at 09:03 AM. Reason: additional info
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Old 06-05-2011, 07:46 AM   #11
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

Thanks for all the help! I am going to show this thread to a buddy who is knowledgeable in electronics and ask him to help me with this. I am hoping that the gauge manufacturers might know what ohms range is used by their senders. Again, thanks.
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Old 06-06-2011, 05:27 PM   #12
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Default Update with New Info: Are There Different Electric Oil Pressure Gauge Sending Units?

My mechanic informs me of the following:

On My gauge:

240 Ohms = 0 psi
33 Ohms = 80 psi

Now that I have these numbers, what am I to look for in a sender, or how do I modify the sender to have the gauge read 30lbs when it is only showing 10 lbs.?

Thanks,
js
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Last edited by Jay Ess; 06-06-2011 at 05:34 PM.
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Old 06-06-2011, 05:42 PM   #13
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

I believe that a Stewart Warner 279A sender will do exactly what you want.
240 ohm at 0, 3.5 ohm at 80 PSI and for an 80 lb gauge.
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Old 06-06-2011, 05:51 PM   #14
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Default Re: Are There Different Electric Oil Pressure Gauge Sending Units?

FYI, Dakota Digital oil pressure sender is a stock GM unit. I thought it would be something exotic.
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Old 06-08-2011, 05:16 PM   #15
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Thumbs up Re: Are There Different Electric Oil Pressure Gauge Sending Units?

Quote:
Originally Posted by hotroddon View Post
I believe that a Stewart Warner 279A sender will do exactly what you want.
240 ohm at 0, 3.5 ohm at 80 PSI and for an 80 lb gauge.
Thanks for the tip but I found one that was made for VDO gauges that was an exact replacement.

Just wanted to thank all that contributed to the thread and helped me solve the problem. The power of the HAMB never ceases to amaze me.

js
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