Oil pressure adjustment

[jimevison]

Oil pressure on my 70 hour Lycoming YO-320-D1A seemed high. I was getting 90 psi WOT on climb out and 65 psi at an idle of 600rpm. Lycoming quotes a high limit of 85 psi and I'd expect around 50 psi at idle. I lowered the pressure using the adjustment screw but found that turning it fully CCW, my idle pressure only came down to 57 psi at 600 rpm. I'd have expected the lower adjustment limit to have been closer to 40 psi. Does this sound normal?

[rwtalbot]

Are you getting the oil hot enough prior to departure, particularly as it is winter over there? W100 or similar is thick stuff and the increased pressure may open your bypass valves and allow unfiltered oil through the engine. Other than that more oil pressure is better IMO.

You should only make changes with the oil hot. Typical adjustment is not more than 3 turns at a time. Personally I would want the pressure at least 50 psi at idle. More is a bonus.

[lr172]

I would not exceed the max pressure. I know it is a lot more wear on the pump, not to mention bypassing the oil filter. I did some research in my hot rod days and the general theme was not "more is better" Guys started using high pressure oil pumps in chevy's, based upon a real need for it in fords and they started burning up oil pumps (same gear design as lycoming).

I would not worry about idle. The engine doesn't need much pressure at idle. If I remember, Lycoming says 25 PSI is low end at idle. Be sure to check that figure, as my memory is not what it used to be. All engines have a lower idle pressure. You should be setting max pressure only. The low end moves with it and if it falls outside the idle pressure spec, you replace the pump or bearings, depending upon the cause. Plenty of old chevys running around with 15 PSI at idle and live for a long time.

Two methods to lower pressure, based upon your setup. Some have an adjustment screw. Older ones, like mine, require you to use washers (as shims) at the end of the spring to adjust pressure. You remove washers to lower the pressure. On the screw, it would be CCW, assuming standard threading.

Larry

[mahlon_r]

Adjusting the relief valve shouldn't effect the idle pressure significantly. When turning the adjustment you are changing the tension on the relief valve spring and this will only effect the pressure at which the ball leaves the seat. So you are really only adjusting the high pressure setting as the ball will be on the seat at any pressure below that setting. 55-90 psi is a cruise oil pressure range not the cold oil take off range. That is normally around 105-115psi max. Idle min is normally 25 psi. If you get the engine warmed up to at least 110 degrees F of oil temp and adjust the pressure to 60 psi at 1400rpm on the ground, you will normally be all set, as this adjustment normally yields about 75 psi in cruise at full operating temp, which is the middle of the cruise operating range and the actual yield setting of the relief valve at that oil flow. Any other pressures like idle and take off are really controlled by engine rpm and oil viscosity due to its temperature and of course internal clearances.
Good Luck,
Mahlon

[ao.frog]

Thanks for chiming in Mahlon.

Valuable info as always! I'm learing something new every day...