I replaced the oil filter housing on my K-Series VVC today with one with a mount for an oil temperature gauge. In doing so I disconnected the capillary tube for the mechanical oil pressure gauge. Quite a lot of oil drained back from the tube, which was obviously largely full of oil. After reconnecting, I guess it was largely full of air. All appeared to work fine, oil pressure gauge was responsive and pressures readings were just as before, but I was just wondering if you were supposed to do anything to bleed the air from the tube? Or just leave it like it is?
SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm
I know I'm resurrecting a pretty old thread but I have (what I consider to be) an interesting observation to share ...
Today I replaced the capillary tube following my minor mishap described here and when I tested it I noticed that although the pressures were reading about where I expected overall, the response of the gauge was very sluggish compared to how it had been previously. If I revved the engine it took a couple of seconds for the gauge to rise and settle. My first thought was that I had kinked the pipe or pinched it a bit tight with a cable tie, but a thorough check found nothing. There were no kinks and it was free to slide through all of the cable ties, which I had only pulled up tight with fingers. So remembering that the old pipe had certainly contained a good deal of oil rather than air when I removed it, I did what instinct had told me to do in the first place and bled it. With the engine running and up to temperature, I slackened off the union at the back of the gauge a little until oil began to ooze out, then nipped it back up tight. The response was totally transformed and tracked the engine speed immediately.
In situations where I may suffer from oil surge I would rather have a rapid gauge response.
I've uploaded a video here. I'm not sure how this responsiveness compares to others.
In equilibrium it is true that the pressure throughout the tube, from the oil filter housing to the gauge, will be the same whether it is filled with oil or air. However when the oil pressure increases suddenly at the filter housing, if there is air in the pipe then a significant quantity of oil must be pumped into the the pipe to compress the air up to equilibrium pressure, which takes time. Similarly when the pressure is reduced suddenly at the filter housing it will take time for the expanding air to drive the oil back out and for the pressure at the gauge to fall.
Oil in the tube, being in comparison to air largely incompressible, does not seem to cause this sluggishness.
SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm
Well done, full marks for perseverance, and a successful outcome. Quick acting oil pressure indicator is much preferred over a sluggish one.
Nigel.
The YouTube video is blocked... please could you bleed it.
Jonathan
@Jonathan - There was a kink in the internet. Try again
SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm
Much snappier.
Thanks
Jonathan
hehe!
Maybe the oil takes time to compress the air as it's pumped through the pipe until it reaches equilibrium (that's a big word for blatchat
)
I'll try bleeding the MGA gauge as that's very slow to react.