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Old 07-30-2011, 05:42 PM
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Mechanical oil pressure gauge problem

I've got an Autometer mech oil pressure gauge being fed by a small bore plastic capillary tube from a T off the fitting next to the distributor (SBC). The gauge had a problem previously where it just stopped working... scared me to death at the time as I thought I had no oil pressure (although the warning light wasn't lit). At the time, I dismantled the gauge (pretty fiddly) and couldn't find anything wrong. The capillary tube was fine and oil wasn't leaking from anywhre. I put everything back together and, as if by magic, the gauge was working again... until now (months later and now attached to a different motor).

The last couple of days, I noticed a slight delay between starting the engine and the needle on the gauge responding. When it did respond (after a second or two), the needle would 'flick' up to the correct pressure reading and then be fine. When I started the engine up this afternoon, the needle didn't move at all... exactly the same symptoms I had months previously. I tried tapping the face of the gauge, but no joy.

Any ideas? When I had the gauge apart before, the mechanism was so simple, I can't figure-out what could possibly be causing this.

Could air in the capillary cause a problem? If so, is there a procedure I don't know about to expel any air before you connect everything up?

Thanks.

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Old 07-30-2011, 05:50 PM
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Sounds to me like the gauge is sometimes sticking or jamming.
Take a really close look at the gears and shaft inside the gauge, something may be bent.
That sometimes happens if the gauge has ever been dropped.
A bit of delicate brain surgery might be able to fix it, otherwise buy another gauge.
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Old 07-31-2011, 04:56 AM
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Thanks, will do... just didn't know if air in the capillary could cause problems as air is compressible and oil isn't. Then again, there always seems to be air in the tube.
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Old 07-31-2011, 05:45 AM
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Quote:
Originally Posted by v8hed
I've got an Autometer mech oil pressure gauge being fed by a small bore plastic capillary tube from a T off the fitting next to the distributor (SBC). The gauge had a problem previously where it just stopped working... scared me to death at the time as I thought I had no oil pressure (although the warning light wasn't lit). At the time, I dismantled the gauge (pretty fiddly) and couldn't find anything wrong. The capillary tube was fine and oil wasn't leaking from anywhre. I put everything back together and, as if by magic, the gauge was working again... until now (months later and now attached to a different motor).

The last couple of days, I noticed a slight delay between starting the engine and the needle on the gauge responding. When it did respond (after a second or two), the needle would 'flick' up to the correct pressure reading and then be fine. When I started the engine up this afternoon, the needle didn't move at all... exactly the same symptoms I had months previously. I tried tapping the face of the gauge, but no joy.

Any ideas? When I had the gauge apart before, the mechanism was so simple, I can't figure-out what could possibly be causing this.

Could air in the capillary cause a problem? If so, is there a procedure I don't know about to expel any air before you connect everything up?

Thanks.
Let me guess, you are using a Fram oil filter.
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Old 07-31-2011, 05:47 AM
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Quote:
Originally Posted by S10 Racer
Let me guess, you are using a Fram oil filter.
?????
Please, just put a new gauge in
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Old 07-31-2011, 05:52 AM
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Quote:
Originally Posted by Richiehd
?????
Please, just put a new gauge in
Might not be anything wrong with the guage. Have had problems with Fram filters before.
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Old 07-31-2011, 06:01 AM
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Quote:
Originally Posted by S10 Racer
Let me guess, you are using a Fram oil filter.
I am (an HP4), but the last time this happened I was using a Purolator, so it isn't the filter. Definitely seems like a problem with the gauge.
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Old 07-31-2011, 06:31 AM
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Usually the mechanical (Bourdon tube) type gauges fail from dirt, condensation, vibration, freezing. A glycerin filled version will survive better as the mechanism is better protected from the elements. It's been a long time since I've used a mechanical gauge, but have fond memories of listening to them tick and the needle swing then having that dinky tube break and dump a quart or so of oil. A good electrical type, IMO, is safer and usually more reliable for automotive use.

Your fix - repair(haven't eliminated the problem) or a new gauge (the best solution - go electric). Your current gauge probably has some dirt or condensation/corrosion in that tiny inlet passage.
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Old 07-31-2011, 07:49 AM
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oil gage

Quote:
Originally Posted by Irelands child
Usually the mechanical (Bourdon tube) type gauges fail from dirt, condensation, vibration, freezing. A glycerin filled version will survive better as the mechanism is better protected from the elements. It's been a long time since I've used a mechanical gauge, but have fond memories of listening to them tick and the needle swing then having that dinky tube break and dump a quart or so of oil. A good electrical type, IMO, is safer and usually more reliable for automotive use.

Your fix - repair(haven't eliminated the problem) or a new gauge (the best solution - go electric). Your current gauge probably has some dirt or condensation/corrosion in that tiny inlet passage.
i'm with I/C on this one.. the bourdon tube is a pain to fill without a vac pump.. i personally would not mess with it..and replace it with either a liq filled or with same as u have.. the liq fill with dampen the pulse's of the pump.. make sure the hole where the tubing is located is clear.. stick a rod in it...
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Old 07-31-2011, 08:40 AM
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First off, a Bourdon tube type gauge has a sealed liquid filled bulb and tube permanently connected to the gauge. A good example is a mechanical water temperature gauge. It is very reliable as long as the tube isn't kinked or broken to let out the liquid. Only the bulb comes in contact with the liquid of which the temperature is being measured. They have decent accuracy depending on the quality of manufacture.

The mechanical oil pressure gauge you are talking about is a direct connection of the gauge and, in this case, the oil supplied under pressure. Anything in the oil can plug the orfice of the fittings or the gauge itself, regardless of the quality or lack of quality of the gauge.

IMO the new digital electrical gauges Autometer and others are selling are of very good quality and are at least as acurate and reliability as the older type guages, probably more so. That's if the gauge is installed correctly and the wiring is protected properly.

With all that said, my guess is your gauge or the fittings and line going to the gauge has something in it. Replace it and the tubing for peace of mind. Flush the oil gallery before connecting the fittings and new gauge regardless of what type you choose to use.

You have to be able to rely on your instrumentation.
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Old 07-31-2011, 10:34 AM
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Since this turned into discussion of mechanical or electric. I like the mechanical oil gauge myself, I do install them using copper and have never had the first problem with the tube breaking. One does need to install it correctly, installing the tube correctly simply means you need a coil, three turns will do it, that allows the motor to move and not effect the tube.

The plastic tube I have never liked because they are prone to failure, electric hate the clunky sender, two failures the, sender and gauge, actually three when considering the wire. I also find the SW brand to be a reliable instrument.

Back to the posters question "'flick' up to the correct pressure reading " my guess it the gauge is sticky, happens to autometer, that fram idea could also have merit, but I would think a zero pressure reading for that. I never use fram so I have no first hand experience on that.
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Old 07-31-2011, 02:54 PM
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Its likely the gauge gone funky. Air trapped in the line will not stop the gauge from reading. Pressure is pressure. The trapped air will compress and slow the gauge needle response time a bit , but not the psi reading itself.

I'd get a new electric oil pressure gauge and sender.
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Old 07-31-2011, 04:08 PM
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Quote:
Originally Posted by F-BIRD'88
Its likely the gauge gone funky. Air trapped in the line will not stop the gauge from reading. Pressure is pressure. The trapped air will compress and slow the gauge needle response time a bit , but not the psi reading itself.

.
Very true, definitely not air in the line.
And if it was a total blockage, the gauge may show some residual pressure with the engine stopped.
That is why I think it is just a sticking gauge, the gears inside are very delicate with very fine teeth. They can jam very easily.
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Old 07-31-2011, 07:45 PM
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This is the electrical gauges that I was talking about. Not the older air-gap movement type. Expensive but worth it IMO.
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Old 08-01-2011, 07:03 AM
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The gauge magically started working again... seems like Silver Shadow is right-on with the sticking gears comment. Will have to tear the gauge apart again and have another really close look.
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