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I'll repeat my suggestion to check the accuracy of your gauge. For either gauge, the difference between 0 and 5 is about one needle's width. I can't find any specs on accuracy, but 5% of a 100 PSI scale is (wait for it...) 5 PSI. For a consumer-grade product, I bet any manufacturer is very happy with 5% accuracy.
In addition, mechanical gauges are most accurate at the top of the range. That's why they have that little pin to stop the needle from moving below zero. For the sake of argument, let's say new gauge is reading 5 PSI low, uniformly across the entire range. For example, 50PSI indicated is actually 45, but this is of little concern as either value is good. When you shut off the engine (actual 0 PSI), the needle would want to go to negative 5 indicated, a big clue it is inaccurate. Instead, manufacturers add that little pin so the needle never goes below zero. They don't want you returning the product as inaccurate when it's actually operating with specifications.
My theory is if you're trying to discern the difference between 0 and 5 PSI, you're asking the gauge to do something it was never designed to do. Analog multimeters are the same way. You're supposed to select a range so the needle is near the top of the band for the most accuracy. If I'm trying to measure 12 volts, a 0-15V range is ideal, not 0-100V or 0-500V. Obviously the "range" is fixed on an oil pressure gauge, but maybe one with a 0-50 range would be better suited. In lieu of that, I'd connect 5 PSI of shop air to the gauge and see what it reads. If you don't have a compressor, a simple bicycle pump would work fine.
I have a box of different gauges. I could try to see if I have one that has a smaller range.
Yes, I do see that it really could be 5 and not zero when I look very closely at the gauge.
I will also try to hook up 5psi of air to the one I have in there.
The pin on the 100 psi guage is set at 3 psi. I'd say it's at least +/- 3 percent accuracy. The confidence interval even higher.
You know your oil pump is running and does very well on a cold start up. No knocking? Drive it! I wouldn't put any Lucas in it unless it leaks oil too. It does stop leaks.
I'll repeat my suggestion to check the accuracy of your gauge. For either gauge, the difference between 0 and 5 is about one needle's width. I can't find any specs on accuracy, but 5% of a 100 PSI scale is (wait for it...) 5 PSI. For a consumer-grade product, I bet any manufacturer is very happy with 5% accuracy.
In addition, mechanical gauges are most accurate at the top of the range. That's why they have that little pin to stop the needle from moving below zero. For the sake of argument, let's say new gauge is reading 5 PSI low, uniformly across the entire range. For example, 50PSI indicated is actually 45, but this is of little concern as either value is good. When you shut off the engine (actual 0 PSI), the needle would want to go to negative 5 indicated, a big clue it is inaccurate. Instead, manufacturers add that little pin so the needle never goes below zero. They don't want you returning the product as inaccurate when it's actually operating with specifications.
My theory is if you're trying to discern the difference between 0 and 5 PSI, you're asking the gauge to do something it was never designed to do. Analog multimeters are the same way. You're supposed to select a range so the needle is near the top of the band for the most accuracy. If I'm trying to measure 12 volts, a 0-15V range is ideal, not 0-100V or 0-500V. Obviously the "range" is fixed on an oil pressure gauge, but maybe one with a 0-50 range would be better suited. In lieu of that, I'd connect 5 PSI of shop air to the gauge and see what it reads. If you don't have a compressor, a simple bicycle pump would work fine.
Karl, I was just about to write basically the same thing you said. You sir are a real time saver!
I probably should post this on the Tools, tools, tools....thread, but I recently got a Makita inflator where you can set the pressure to what ever you want. I was wanting an on board inflator and looked at various types, that plug in the cigar lighter with a long cord etc. But heartily endorse the makita inflator. I also tried a neighbor's Ryobi inflator. Another good choice.
Heres the latest test.
3 gauges.
1st at startup
2nd at 1000RPM in park (when fully warmed up)
3rd in drive with foot on brake approx 600 rpms (fully warm)
Guage appears to read low at low RPM. At least it shows an increase with 400 more RPM. The rule of thumb is 10 psi per thousand RPM, warm. How are you determining RPM?
For testing your guage you'll have to put together some plumbing. Guage to Schrader valve fitting most likely.
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