oil pressure gauge pipe

[markmark2]

Hi all, just a thought with regard to a previous post re fitting an oil pressure gauge. If the pipe from the t-piece/sender to the gauge was full with oil as opposed to 3/4 before the engine is started, would the oil pressure increase? If so then the pressure displayed on the gauge would that be a little bit out?

Cheers

Mark

[wilf]

Cue 15 page discussion, lol.

IMHO it makes no difference, other than a full capillary tube will make the gauge less responsive especially when the ambient temperature is well down. (just the viscosity of the oil in the tube).

[jleyton]

Interesting subject which has been discussed (without conclusion ) on here before.

The consensus seemed to be that some air in the pipe wouldn't really matter. However, I was of the opinion that some (compressible) air would have an effect.

Starting my car up after fitting an OPG, I was a little disappointed by the pressure. I disconnected the pipe at the gauge and carefully topped the pipe up with 3in1 (only because the container was more convenient) and the pressure reading seemed more instantaneous and a little higher.

Either way, I guess it doesn't make a big difference.

Cheers

Julian

[milothedog]

Interesting subject which has been discussed (without conclusion ) on here before.

The consensus seemed to be that some air in the pipe wouldn't really matter. However, I was of the opinion that some (compressible) air would have an effect.

Starting my car up after fitting an OPG, I was a little disappointed by the pressure. I disconnected the pipe at the gauge and carefully topped the pipe up with 3in1 (only because the container was more convenient) and the pressure reading seemed more instantaneous and a little higher.

Either way, I guess it doesn't make a big difference.

Cheers

Julian

When we use to recharge the accumulators on hydraulic power brake systems after repair/replacement the test equipment that was connected to the hydraulic side had bleed valves to remove any air pre gauge before making any pressure adjustments.

Some Rolls Royce, Jaguar XJ40 (I believe) and some Citroen's have charged hydraulics brakes, I would be interested to hear if the procedure was/is the same

Ian.

[Graham Pops]

I have a dual water temp/ oil pressure gauge to fit and have purchased a stainless steel braided pipe in lieu of the plastic one supplied which many owners do. On the Demon Tweeks site where I bought the pipe it states:" These pipes are used to transfer fluid from the engine compartment to the pressure gauge."

Other suppliers to the motor sport trade discuss the pros and cons between electrical gauges and mechanical gauges as oil in the pipe entering the cockpit is seen as a potential risk in the racing world.

So its oil in the pipe for me but how to do that without leaving an air lock or covering me/car in oil is the challenge!

[Lingen]

Graham. It is easy to get the pipe filled with oil. Disconnect it from the gauge, stick the end in a container, and start the engine. There is absolutely no risk whatsoever of covering everything in 20/50. It will just trickle out slowly as the pipe has a very small bore. Let it run for a bit to clear any air. Switch off, and re-connect to the gauge. Simples.
Mike.

[SaskStag]

..from the medical world. We measure arterial blood pressure using a catheter inserted into an artery (under anesthesia) connected to saline-filled non-compliant tubing and an electronic transducer (converts pressure to an electrical signal). The arterial pressure changes fairly quickly with systolic and diastolic pressure (unlike oil pressure??) and the ability of the system to respond to changes depends on the resonance of the system and anything that might dampen the signal. A column of air is compressible so will dampen a rapidly changing pressure, so the peak and trough accuracy is lost, but mean pressure might be believable. Therefore, we take great pains to remove air bubbles (as well as flushing air into an artery isn't a good idea anyway). Therefore I am guessing that a constant pressure might read ok with some compressible air in system, but response time to changes would be dampened.

But I'm no physicist or mechanic.......
Tanya

[Graham Pops]

Thanks Mike. Hopefully it will be a trickle that will give 50 psi on the gauge!

[Stagsongas]

But I'm no physicist or mechanic.......
Tanya[/B]

Maybe not Tanya, but you're 100% correct.

Air is indeed compressible and would make an effective buffer or damper, slowing down the reactions of the instrument when reading low to high for instance. The eventual pressure it would indicate would of course be the same, it would just take longer to do it.

That's isn't a big problem in a car but the trapped air will include water vapour which promotes internal corrosion. If it were an Aircraft we'd be bleeding it for sure. None of this may ever matter in a car, but for the time it takes (seconds) I thought it worth doing a job well.

I also binned the nasty, kinky plastic tube and fitted copper instead.

Regards

Steve

[wilf]

Still disagree.

Air in the pipe would introduce some "bounce", but having a pipe full of cold, viscous, oil must surely introduce a far greater delay to the gauge's responses? Because, due to the nature of the gauges internals, the oil must actually move in the pipe to move the needle.

And copper isn't a good idea as engine vibes will work harden it and leave it prone to cracking. Aeroquip make a better product for this application.

[38rover]

When we use to recharge the accumulators on hydraulic power brake systems after repair/replacement the test equipment that was connected to the hydraulic side had bleed valves to remove any air pre gauge before making any pressure adjustments.

Some Rolls Royce, Jaguar XJ40 (I believe) and some Citroen's have charged hydraulics brakes, I would be interested to hear if the procedure was/is the same

Ian.

Rolls Royce Silver Shadow about 66ish and on have a hydraulic system that controls the brakes and suspension in one system pressure is maintained by 2 accumulators which are pressurised from a rod from the cam shaft the system is bleed with the engine running from beneath the car fit the hose to the bleed nipple into a container up to 1 ltr of very expensive fluid before the air is out brakes are bleed at the callipers in the normal
way.
The modified system is under licence from Citroen.

[TR5convalescent]

Um, doesn't it all bleed back into the engine, or is there a no return valve?

[Pete]

I doubt it. It will be like closing one end of a straw with your finger after it has been dipped in a glass of water. The water doesn't run out of the straw once it is taken out of the glass.

[TR5convalescent]

Of course! Thank you. I was chucked out of physics class in 1969.