Oil Pressure Gauge

[Legal Bill]

Hello everyone. I hope all are well.

The oil pressure gauge my '65 Healey 3000 MKIII vibrates, flickers or shakes. I'm trying to attach a video so you can see what I mean, but it doesn't work, so here is a description. The gauge still goes to 0 when the engine is off. The needle still swings to the 65-70 psi range when it starts, but the needle flutters between 50 and 80 psi. When hot at idle, the needle flutters between 10 and 35 psi. The needle is still in the same range as it was before this problem started, but it flutters almost all the time. Not always, but almost always. If you want the vid, send me your email and I'll send it to you.

I tried "bleeding" it. I never needed to do that before with a Smiths gauge, but I gave it a try. No change.

The engine has less than 1,000 miles on it. It was rebuilt about 15 years ago and I don't use it much. The car lives in a climate-controlled garage.

Any ideas what is wrong here? I do not have another oil pressure gauge that I am confident works.

 

[BoyRacer]

My first question is - did it start doing this right after you had it rebuilt? The reason I ask is that the fitting on the block has a very small hole in it to let the oil through. The purpose of such a small bore is avoid pulsations. Was the bore possibly enlarged by the rebuilder?

 

[Bob_Spidell]

Disclaimer: Following is hearsay.

I've heard there should be a small pocket of air in the line, which of course will be near the gauge. This air helps to damp pulses from the pump (sort of like oil/air shock absorbers). Some claim you need to bleed the line but 1) oil will drain back when the engine is off anyway and 2) I've never bled the line and haven't had a pulsing gauge.

I've tried to think of a way that a failing pump could cause this but can't come up with anything (maybe a vane stuck in its slot in a rotor-type pump?).

 

[Healey Nut]

Look at the inlet pressure connection , the hole should be very small . The small hole is designed to eliminate the pulsations of the pump causing needle to bounce .

 

[BoyRacer]

I've reconsidered my answer. The oil pump pulsations are not causing your gauge to fluctuate as much as you describe. There is a gearing mechanism inside the gauge that transmits the movement of the "C" shaped Bourdon tube to the needle. The Bourdon tube itself should not be rapidly expanding and contracting. I think there is something loose inside your guage.

 

[Legal Bill]

Update. I removed the steel pipe from the car (flex line to gauge) and cleaned it out. There were bits of material in the pipe. After I cleaned it (as well as the connection at the back of the gauge) I reinstalled the pipe and the gauge was fine. So where did the bits if material come from? I'm betting it came from the flex line.