Tio 540 oil pressure

keithdvm@hrtc.net

Hi all,

I have a 05 T182T with approx 1700 hrs. Recently Ive complied with Lycomings 400 hr "wobble" test which required reaming the exhaust valve guides (engine had morning sickness). Mech also adjusted idle down somewhat as it was too high. Now engine starts and runs very smoothly however my oil pressure is now fluctuating with engine rpm. Cruise OP at 22 squared is 56-58 which is barely in the green arc, oil temp 190-195. Yet post flight when taxiing, OP is showing 35-36, well out of green arc. I realize adjusting Idle down could decrease OP, but Ive never had such low readings in 3 years (350hrs). I am not sure if I should be concerned. I cannot get an answer from ANY mechanic. Lycoming recommends 60-100psi cruise, no less than 25 idle. All of my Blackstone oil analysis have been completely normal. I have several cross country flights coming up for business and dont know if I have a developing problem or not. ANY advice would be appreciated.

Thanks Keith

Scott Sherer

Stand by while I send this to our association A&P, Erich Rempert.

planewrench

If your oil pressue is in the green in cruise power settings I'd say you are fine, as long as not dropping below idle requirements. Eng showing its age. As a experiment, switch oil to a straight weight and see what she does. You could try new spring in the adjustable oil pressure valve, as well as look for any descrepency in the ball to seat areas. You didn;t say this was sudden change so i am making a assumption this was gradual event. If sudden after the work, start with smutz in the relief valve areas.

keithdvm@hrtc.net

thank you for the advice. I had considered adjusting the oil press valve (adding a washer or 2) as it is my understanding each washer should increase OP 5psi. At least investigating if gunk is stuck under ball. Mechs also adjusted prop governor (to get rpm up to 2400 , was only 2300+) and I wonder if this had anything to do with OP. otherwise plane runs great.

Scott Sherer

Here's a response from our association A&P Erich Rempert:

At idle you have 35 psi while hot, 25 is the minimum. This means there is plenty of oil volume and the engine has reasonably acceptable tolerances in the bearings still.

In cruise you have 56 psi, the green arc starts at 60 psi. That has nothing to do with idle speed obviously; Lycoming engines have adjustable oil pressure relief valves, I would find a mechanic who will take it apart and check the ball and seat, resurface or replace if necessary, and adjust the pressure to be in the green at cruise.

Do this as soon as practical but I wouldn’t cancel any plans over it.

100 psi is the maximum at start up with cold oil, exceeding it can blow out gaskets, damage the oil cooler, and possibly damage the oil pump itself. 100 psi is not the “goal”. 

Oil must reach a minimum of 180*F to boil off moisture and prevent acids from forming in the oil, 190-195* is what I’d like to see.

~Erich Rempert, IA Consultant