How to calibrate oil pressure gauge?

[TomO]

Actual oil pressure is not important to me. I just want to know that I have pressure and that it does not change from what is normal for my car. A change from normal, will let me know that something is not right and I better pull over and check it out.

Calibrating the sending unit to the gauge can be done at the sending unit.

Incorrect gauge readings can be caused by poor connections or poor grounding.

[Jack E/NJ]

Here's the diagram from the HAMB. As mentioned, poor connections could be an issue as well as tired/broken bimetallic strips or points, or heater coils in both the sender and gauge. Probably a good test is if you can detect a pulsing needle movement in the gauge when turning the ignition on without starting the engine.

Jack E/NJ

[Charlie ny]

Henry,
I'd do what Pete suggested....NOS dash gauges are easy to find even at
small swap meets. I'm pretty sure the fuel and oil pressure gauges are the same,
just change the face. Adding a rheostat to me isn't where it is at, not that anyone
asked.
Charlie ny

[41ford1]

I'm Charlie NY on this. Adding a resistor shunt is not the solution. How much of a difference are you trying to eliminate? You might be able to "fix" it by replacing the 80# sender with A 60# unit. A Standard Motor Products PS 60 is a direct fit. It will set you back about $15.00. The electrical part of the sender/gauge system is the the same. What changes is the dial face markings and the sender diaphragm. So if you use a sender with a lighter diaphragm the gauge pointer will move higher on the scale.

[Tinker]

Originally Posted by Jack E/NJ

The old sender is better suited to an idiot light than the idiot gauge. 8^)

Jack E/NJ

I like mechinacal guages for this reason. It seams the standard guages are just an approximent suggestion of the condition.

But maybe there is a hack for this...

[Teich]

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I don't think you can adjust the gauge, tried that-- had a gauge apart and a sender, there are adjustments in there as well, in the end never got any better. To get a gauge closer try using the sender from 1957 Ford truck with a gauge it may work if not get the gauge as well (change the face and needle) and install that should all work. I converter my car to 12v, I used Temp,Oil, and Fuel gauges,(changed the gauge faces and needles) used the Ford volt. control from truck. Used the senders that match gauge, the fuel sender was the so called replacement for the original gauge. All work very nice now. Laurie

[robert shreveport]

Old Henry, try contacting Tom Wesenburg on the model A forums, he is really good on this kind of stuff. Good luck and post back if Tom is helpful, he enjoys a challenge.

[Old Henry]

Originally Posted by 41ford1

You might be able to "fix" it by replacing the 80# sender with A 60# unit. A Standard Motor Products PS 60 is a direct fit.

I just ordered one. We'll see if it helps. Makes sense that it would.

Thanks for the idea.

[Old Henry]

Originally Posted by Tinker

I like mechinacal guages for this reason. It seams the standard guages are just an approximent suggestion of the condition.

But maybe there is a hack for this...

Yeah, that's why I have the mechanical gauge but I'd still like to get the stock gauge more accurate if I can. The 60# Standard Motor Products sender seems like it might be just the hack I'm looking for. I've ordered that and will try it and see.

[Old Henry]

Originally Posted by 41ford1

I'm Charlie NY on this. Adding a resistor shunt is not the solution. How much of a difference are you trying to eliminate? You might be able to "fix" it by replacing the 80# sender with A 60# unit. A Standard Motor Products PS 60 is a direct fit. It will set you back about $15.00. The electrical part of the sender/gauge system is the the same. What changes is the dial face markings and the sender diaphragm. So if you use a sender with a lighter diaphragm the gauge pointer will move higher on the scale.

Originally Posted by Old Henry

I just ordered one. We'll see if it helps. Makes sense that it would.

Thanks for the idea.

Got the Standard Motor Products 60 lb. sender in today and installed it. It did change the reading on the gauge. Unfortunately, now, instead of the stock gauge reading half of what the mechanical gauge shows, it shows double, so, the stock gauge now shows 80 psi when the mechanical gauge only shows 40 psi. Ah, what the heck, it was just a $20.00 risk. I think I'll just order a new stock sender and hope it's more accurate than the one I have now.

(Yeah, I put the old sender back in. Better to read too low than too high.)

[41ford1]

Reading to high is easier to deal with on the OP system. If you want to experiment try a 10 ohm resistor in series between the gauge and sender. See if that gets you closer to the mech gauge.

[Old Henry]

Good idea. Even better - I'l put the POT in series. Then I can adjust the resistance and see how much it takes to match the mechanical gauge. If I can get a match I can then just buy a resistor the correct ohms, install it, and have a permanent hack.

[Old Henry]

So, I put the POT in series between the gauge and the 60 lb sender. Same result trying to reduce the current through the oversensitive sender as when trying to bleed current past the stock too restrictive one. No balance was possible. Up to 5.2 ohms the gauge read double just like the sender read without restriction. At or over 5.2 ohms the current shut off and the gauge read zero regardless of the pressure at the sender.

As concluded previously, because the sender is not varying the current like a rheostat or resistor but is actually switching it on and off at varying rapid intervals, varying the resistance between it and the gauge has no effect below 5.2 ohms resistance and cuts off all current above that.

[Old Henry]

P.S. For anyone struggling to remove their oil pressure sender, Snap-on Tools makes this handy tool just for that purpose that works great. Just have to break the spring holder off of it at it gets in the way of our fatter senders. The Snap-on part number is S6156.

[SofaKing]

This may be a little late in the discussion but what about taking both to a calibration lab and having them tested? You may find the mechanical gauge isn't all that accurate either. Your objective appears to be getting an accurate oil pressure reading and judging from the tools and effort you're going to pursue this pretty relentlessly. If you take both to a cal-lab you will have an accurate baseline and from there you can decide how to proceed. There are certified cal labs in the SLC area that work to NIST standards, maybe they can help.

[Old Henry]

Originally Posted by TomO

Actual oil pressure is not important to me. I just want to know that I have pressure and that it does not change from what is normal for my car. A change from normal, will let me know that something is not right and I better pull over and check it out.

Same here. My main concern is when I'm idling at a stop light and my dash gauge says zero oil pressure. If it said anything above zero I'd be fine with it. So, I have to open my glove box and look at the mechanical gauge that never shows lower than 20 psi. That's what I'm mainly looking for - the same as TomO - just to show some pressure on the dash gauge at idle. But, not 40 lbs. that the 60 lb. gauge shows. It's not a big deal. Just a curiosity about whether the stock dash gauge and/or sender can be calibrated in any way. So far it looks like neither can. As I said before, if it continues to bug me I'll just buy a new sender and hope it makes the gauge read more accurately.

[cmbrucew]

Prof
A 20 pound pressure switch and a small light will do what you want.
Have a happy Easter.
Bruce

[estout81]

Old Henry,
Read post #8. The sending puts out pulses. 120/min. = mid scale on gauge.

[Old Henry]

Originally Posted by estout81

Old Henry,
Read post #8. The sending puts out pulses. 120/min. = mid scale on gauge.

Originally Posted by estout81

3 volts (two D cell batteries in series) should read full scale and 1.5 volts (one D cell battery) should read 1/2 scale. Hope this helps.

Yeah, I tested mine right after you posted that and that's about what my gauge does. And I could totally control the gauge with the pot. That's why I thought it might work either in parallel or series but it wouldn't with the cycling switch in the sender.

[41ford1]

Now you really have my curiosity up. What is are the specifics on the POT you are using? Can you provide the maker and specs on it? estout81 is absolutely correct the output of the sender is pulses. These gauge systems have a slow response. So don't look for rapid changes. The gauge is nothing more than a resistor wire wrapped around a bimetallic strip. More current though that resistor = more pointer movement. Increasing the resistance that the sensor is driving should reduce the pointer movement not kill it. It may be time for me to put together a test station.
I do know the fuel gauge works with a resistance type sender. And the battery voltage (not Ammeter) gauge reads correctly with a 60 ohm resistor in series on 12 volts.