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oil pressure gauge line.

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[ QUOTE ]
Sometimes there are pulsating pressures in the oil system that just vibrate the gage needle up & down a bit. This only wears the delicate gage internals more than necessary.
D

[/ QUOTE ]

Hi Dave,

In the above quote, you mention the gauge internals becoming worn - does a gauge, in fact, wear out? Mine's been acting a little weird lately - a couple of days last month, upon starting car up in a.m., gauge went up to about 42 lbs. after reving engine while idling, with no difference when increasing rpms to about 2700 in neutral. Drove around a while and it started behaving like normal - 35 lb. in neutral and 55 lb. at 3000 rpm.

Over this past weekend (400 miles round trip), Saturday everything seemed OK - 35 lb. in neutral, 55 lb. at 3000.

Sunday, between 2500 to 3000 rpm, it read 42 lbs much of the way home, then began operating again, but everything seemed about 8 lbs. too low - 27 at idle and 47 at 3000 rpm.

This morning at start up in the garage, it was idling at 35 lb. again. When I revved it up to 2500+, the pressure would go up, but coming back down, kind of got caught at 42 lbs. and stayed there. When I shut the engine off, the needle didn't go down smoothly, kind of hesitated at a couple of spots. Is this just the gauge, or someting bigger, like (groan) the engine??

Didn't have time to take it out today to see what the reading was at 3000 rpm.

Sharon
BN1
 
Hi Sharon,
Yes, these gages do wear mechanically. The gage is basically a thin walled C shaped tube That is anchored at one end with the free end attached to gears. The tube tries to straighten out with pressure increases & vs. This movement of the tube end is coupled to the indicator needle through a rack & pinion gear. These small clock like parts can wear, their pivots can wear, & dirt can get between the delicate parts. Any of thes can cause the needle to stick in certain spots or otherwise act strangely.

The temperature gage is constructed much the same but it doesn't move nearly as much or as often as the oil pressure gage & so lasts a lot longer.

If it appears to be stuck, a light rap will often free it. They can be repaired but because there are both the oil & temp gages in one housing, it can be quite expensive. I have threatened to have mine repaired, but for now, I just give it a rap when it gets stuck. It is still quite accurate otherwise.

MoMa or Palo Alto, or Nisonger can repair it for enough dollars. Mainly I hate the turnaround time to be without the twin gage.
D
 
Dave,
Thanks for the quick reply and comprehensive information - very interesting! It's always something with these cars (my car, anyway). I think I'll start with the easy things first and try rapping on it in the morning. Thanks again.

Sharon
 
Dave,

A great description of the oil pressure gauge and how it works. The "C" shaped tube to which you referred is called a Bourdon Tube. The Company "Gauges Bourdon" is still in existence. The Bourdon Tube is still at the heart of a large percentage of industrial pressure gauges.

Mike Brooks
(Instrument Engineer)
 
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