VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Vibration in oil gauge

This is also posted in the 1912-28 Forum

Fellas,
I have an interesting problem. I am using 10W-30 oil in my '28 Coupe. It has about 15 lbs oil pressure at idle cold and 25+ lbs at higher speeds. The gauge needle is steady as a rock. As the oil heats up the pressures drop to about 5 lbs idle and 15-20 at speed. None of that is the problem. However as the oil heats up the pressure gauge needle begins to slowly vibrate and then when the engine is fully heated vibrates so much you can't tell the high pressure. At idle it is steady. What is the cause? Any ideas?

Did you try another gauge to see if the problem still persists?

Not yet. If it is the gauge why is it steady as a rock when the oil is cold?

Hey, it's a Chevrolet! You should know by now that vintage Chevrolets do goofy things at times.....and for apparent no reason.

the valve in the oil distributor fluttering?

That is another thought I had but was trying to eliminate the easier and cheaper to fix possibilities first. It take removing the pan to check the oil distributor valve on a '28.

Chipper,

I don't think you need to remove the oil pan to inspect the oil distributor valve. Simply remove the oil lines from the "T" brass fitting in the block below the carburetor. (Leave the smaller single outlet brass fitting in place as it will retain the housing in place and there's nothing under it anyway, just a passageway) Below the "T" brass fitting there's a 9/16" hex on the fitting, hold it while loosening the large 1 1/4 jam nut. once it's loose simply remove the whole fitting assembly using the 9/16 fixed hex on the fitting. Don't loose the copper washer under the 1 1/4 nut. Once the fitting is removed the spring/valve assembly will lift right out. I'd be surprised if you find anything.

Oldie,
Thanks for the information. I will try it if the air bleeding does not work. When I cleaned the internal oil lines I took the valve apart inspected and cleaned the valve. All looked good at that time.

I had one suggestion of a weak spring on one vane of the oil pump. Seems plausible.

It is the cold steady needle, hot vibrates to a blur that has me baffled. Why should the oil viscosity reduction have such a dramatic effect? Yes I understand the damping effect of viscosity but still don't feel it should be that dramatically different.

Of course there is the harmonic resonance that is dependent on the system dimensions. Thought about putting an insert in the line to reduce the diameter as flow is not a factor. Then felt I was doing too much thinking and that someone else must have had the problem in the past and solved it. This can't be as complicated as rocket science. Beside I understand a bunch of that.

Why not disconnect the oil line to the gauge and install another gauge, any kind of gauge that's appropriate for the system and see what happens. Installing an orfice in the line may souve the problem but cover up a condition that should be resolved. Better yet, place the test gauge at the engine end of the oil line and see what happens. That's easier than working under the dash and the mess is easier to clean up.

Are you operating with an original style oil filter and if so is it starting to restrict the oil flow? Actually all the valve does is bypass the filter when the filter is restricted.

The same condition was experienced on my 27 and did
many of the above ideas, it finally was corrected by
replacing the vane spring which was in two pieces when removed.
I found a used pump and took the spring from it and it worked fine even tho it was not the exact replacement.

Roy,
That is not exactly what I wanted to hear but sometimes the truth hurts. Will try a few things to see if any help but may need to pull the pan and maybe engine again.

Weighing in late as usual, all the previous suggestions are great and I can't add anything constructive.

However I have had to deal with vibrating needle (pointer) on pressure gauges on continuous running diesel engines, especially on the fuel system. The trick is to dampen the pressure on both ends of the gauge circuit, in other words at both the source and the gauge end, using the volume of fluid in the supply line as a damper.

If in fact you discover a problem, then I would say leave it alone, it is your best diagonstician.