[sphynx88]

I'm troubleshooting why my oil pressure gauge is always at 0. When I test the gauge, taking the wire off the sender, it pegs to the right. However when I ground the wire it only hits the middle. Should this peg to 0?

[Half-Inch Stud]

I think so. But my calibration note are not hndy to verify.

Open Sender pegs above 80 PSI. Think it pegs on zero at Key-turn for gauge check.

Those gauges work on 0-90 magnetic ratio,, and only go out of cal when the needle can twist on the shaft.

[dataway]

Gives me a good idea, maybe I'll build a small air tank with various adapters to fit pressure gauge senders, with a good quality air pressure gauge on the tank should be able to check the accuracy of either electric or mechanical gauges.

[lust4speed]

Originally Posted by dataway

...with a good quality air pressure gauge...

That's the real problem. Every mechanical gauge I own reads different. Easy to toss out a gauge that reads way off from the others, but there is always a grey area where I have a choice to believe 58, 60, or 61 pounds. Seems also that additional money spent on more expensive gauges still has those expensive gauges disagreeing on an exact number.

[Bill Hanlon]

Segal's law. "A man with a watch knows what time it is. A man with two watches is never sure."

[Mr Anonymous]

My father sold industrial valves, thermometers, regulators, etc. Following his passing, I have been going thru the "stuff". I ended up building a pressure test rig because of concerns over which tire pressure gauge was correct. Using my air compressor, a good regulator, a tee to accept various NPT adapters, and so on. It was a fairly interesting rabbit hole. I have a highly accurate, 6" diameter, brass, 0.-100psi gauge. I tested it again a handful of 'very decent' quality gauges, and found about 3-4 that 100% matched the Big One. I accepted it as a standard, although technically they could all be reading the same wrong pressure. I considered that the law of averages would to mean that the Big One and these others are likely "correct" enough for my purposes.

I checked a gaggle of other pressure gauges (oil pressure, tire pressure, etc) on my "test rig". I ended up throwing out about 50% (I had a lot). The worst offenders are the small handheld round gauges with the 1" long tire valve attachment coming right off the gauge. The kind you get near the checkout counter at any parts store. At an observed 50psi test pressure, there wasn't one within 5 lbs, and one that was off by 12! There's a reason they are cheap!

Those "pencil-type" tire pressure gauges are closer than you'd think - stangely enough.

Later on, said "test rig" was reconfigured as a leakdown tester for a car I was diagnosing. 3 dead cylinders out of 8. Ugh.

[dataway]

Typically places like McMaster sell certified gauges that are within +/- 1% ... probably close enough as a standard for our purposes. About $100 though.

Accuracy is fun. I have a Starrett master level I use to check my Starrett machinist levels that I use to check my regular levels

Good mechanical oil pressure gauges usually have a method for adjusting them, have to remove the rear case and typically there is a small mechanical link with a "U" shaped kink in it that you tweak to adjust the reading.

[steve25]

Of the 50% you tossed out how many where on the low side of reading right, as I could live with that!

It would be interesting in testing how much the reading are off as pressures change also , are they whatever percentage low or high up to the maximum pressure that they will need to read at?

[Mr Anonymous]

Since my "master" gauge was 0-100psi, I checked at the middle point of the range for 100 psi gauges I was checking - since the very low and very high end of the range has traditionally been considered to be less accurate. When doing the 0-60psi cheapies, I tested at 30psi, the middle of their range.

>Of the 50% you tossed out how many where on the low side of reading right, as I could live with that!

Some were low, some were high. Very random. All junk.

[Poncho60]

If I had an older Pontiac where the idle pressure was allowed to be pretty low but still considered acceptable, I would be way more concerned about 2-3 psi variation there than at the higher range. JM2C.

[Half-Inch Stud]

Originally Posted by dataway

Typically places like McMaster sell certified gauges that are within +/- 1% ... .....Good mechanical oil pressure gauges usually have a method for adjusting them, have to remove the rear case and typically there is a small mechanical link with a "U" shaped kink in it that you tweak to adjust the reading.

Yes. Most round pressure gauges can be tuned-in at the "U".
Fun fact; most electrical gauges are tuned by a screw on the spring tension.