How to calibrate oil pressure gauge?

[Old Henry]

I'm tired of my stock dash gauge reading so much lower than my mechanical gauge. I took the gauge mechanism out and see two adjustments inside that can be made. Has anyone every adjusted that gauge and know how? Here's the inside:



You can see two sets of teeth overlapping a hole at 1:00 and 8:00. Which do I adjust and which way?

[Old Henry]

OK. I messed with the left one. It sets the zero point. I'm going to hook up the gauge and mess with the right one to see which way increases the readings.

[fordor41]

I'd say wire up the stock gauge off the dash and adjust to match your other gauge while the engine is running. I assume the two adj, are for min. and max. If you can't get the two to match maybe the sender is bad.

[Terry,OH]

I remove the sender and squirt brake cleaner into the diaphragm (brass) to clean out all the old caked up oil. Sometimes have to start with a drill bit (by hand only). Then use air pressure on the sender and connect the gauge and battery. Do your calibration.

[Old Henry]

As I was messing with this thing it all came back to me that I had tried to "calibrate" this gauge years ago. In fact, there is no adjustment of its "sensitivity" to the signal it gets from the sender. The left teeth are for setting the needle to zero. The right teeth are used for installing the needle to secure it. Loosening it just loosens the needle so that it flops back and forth and is not tight. Hopefully I remember this attempt longer next time and not take the time to remove it and mess with it again.

I have replaced the sender a few times and it doesn't seem to help. That does appear to be the only way to try to get any more accuracy out of this gauge. Good I have my mechanical one. I'll just keep counting on it. It just bugs me to have something not working perfectly if it's possible to make it so. Now that I know it isn't maybe I can relax.

[Pete]

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Watch for gauges at swap meets. Buy up a half dozen. Try them till you get one that reads right.

[tiquer]

Henry for the sender to work it needs a good ground if the threads are dirty or rusty or painted trouble will follow

[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.

[Bruce Lancaster]

On the ground...the actual engine ground is often poor, if there isn't a ground cable over to where ground cable attaches to body. Ground path has to go through mounts, rusty fasteners, dirt, etc. With engine running, see if a jumper from sender to battery ground post does anything to reading.

[Jack E/NJ]

The pressure gauge is really just an on off switch due to the diaphragm switch. Pressure or No pressure. The intermediate pressure is really a fake intermediate measurement due only to the heater wire heated up more as the block oil heats. That's why I use a mechanical oil gauge.

See http://www.jalopyjournal.com/forum/t...enders.428126/ for diagrams.

Jack E/NJ

[johnh7]

It would be nice if there was a way to adjust the reading on an original gauge. Maybe some of you who are very into electronics can figure out something inline between the sender and the gauge that will change the reading to match a new mechanical one?

[Ross F-1]

I've had some luck adjusting the one on the right in Henry's picture. Very small tweaks make a significant difference, and it takes a minute for the change to occur. But Jack is right, it's not a precision system. Guys have adapted 70's Ford gauge units to their stock truck dash, some of them are almost the same physically as the 48-52 Truck originals, but they work on variable resistance (so you need to use the newer sender too -- which cost about a third of what a typical original sender costs).

[41ford1]

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.

This method will get the gauge real close. The adjustments of the gauge are as you first stated, zero and span. If you move the zero position the span/tension adjustment needs to be made to compensate for that change. Too much tension the needle wont move full travel. Too little tension the needle will be lose and not indicate. Adjusting these is a balancing act.

[Old Henry]

Originally Posted by johnh7

It would be nice if there was a way to adjust the reading on an original gauge. Maybe some of you who are very into electronics can figure out something inline between the sender and the gauge that will change the reading to match a new mechanical one?

I've got it! A rheostat to bleed some of the current coming out of the gauge to ground bypassing the sender that's restricting it too much! I'm going to try it and see how it goes. Should work great. We'll see. I'll start with a spare gauge light dimmer that I have on hand and see how that goes.

[Old Henry]

Well, that didn't really work as I thought it would. With the ignition on but the engine off I could totally control the position of the gauge needle with the potentiometer (POT for short -modern term of rheostat) so I thought it was going to work. But, when I started the engine with maximum resistance on the POT then let the gauge get up to what it would do on its own, I then started reducing the resistance on the POT hoping that I could bleed enough current past the sender to just boost the needle slightly. But, as soon as I dropped below 50 ohms the needle went to max and there was no way to get it to be anywhere in between its natural setting and max with the POT. I was hoping that, if I got the needle to read right with a little bleed past, I could then measure the resistance in the POT and buy a resistor that ohm and install it permanently to get a boost. Apparently not. Shucky darn. Thought I had something there.

P.S. I also tried adjusting both oil pressure gauges that I have with the set of teeth on the right but, although I think a very slight adjustment let the needle go to the right just slightly more, any further adjustment than that to try to get the needle to where it should be just loosened it so it just flopped back and forth. So, that set of teeth on the right really isn't sufficient adjustment to solve the problem.

[Jack E/NJ]

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

Jack E/NJ

[BillM]

I think you were putting the pot in parallel with your sender; I think you may have better success putting it in series. See this thread for typical resistance values for resistance style senders which shows that higher resistance in the sender makes the gauge read higher. See post no. 6. https://www.fordbarn.com/forum/showthread.php?t=131598
You may find a resistance that will correct the reading at one end of the range but the the rest of the range will still be off; a linearity thing.

[Old Henry]

I'm afraid that's backwards for what I need for my sender and gauge setup. In the thread that you linked to the gas gauge the goal was to reduce the reading by adding a resistor in series in the line. I, and most with low reading oil pressure gauges, need just the opposite - greater current to deflect the needle more toward the higher, more accurate readings.

[Mike B]

If you used the POT as a variable resistor, that may be your issue, the POT should have 3 legs, one shunted to ground..between the other two is like a Rheostat, but you have to leak the excess current to ground to have the POT, function like a POT, and not a Rheostat...just recalling Mr Jackson's HS Electricity class I took...hope I understood him correctly, if not..well, can;t blame him

Edit:

I used "Rheostast, but should have stuck with "Variable resistor"

[Old Henry]

That's what I did. The current coming from the gauge was connected to the center, or variable, post and one of the other posts at the ends of the rheostat coils was connected to ground.