Low Oil Pressure

[Renaud]

Hi everyone !

I am struggling with a low oil pressure issue on my Aerovee. If anyone has suggestions, please let me know your thoughts, I really need help here, this issue is driving me crazy...

Set-up:
External oil cooler under the engine, full-flow connection to the oil pump cover (two hoses).
Oil pressure sender is new, VDO.
Oil pressure sender fitted to the by-pass plate at the top of the case, as per Aerovee manual.
Oil: 20W50

The issue:
Oil pressure is ~normal with cold engine (45/60 PSI at 3000 RPM), but after ~15min flight and as the oil gets hot (175°F), the pressure decreases to about 15 PSI at 3000 RPM instead of the expected 40/50 PSI. (When hot the "idiot light", which is set at ~12PSI, lights on as soon as I reduce RPM)


What i already checked:

- Pressure sender and gauge were tested with air compressor and gauge. Pressure indication on the aircraft gauge is correct. The idiot light actually triggers at its nominal trigger pressure

- Pressure relief and regulation plungers are free to move, surface finish of the top and the sides are OK, top surface of the holes in the case are OK too. Springs are in the right place (not inverted).

- I tested increasing the compression of the pressure relief spring with a washer (Flywheel side), it does increased the cold temperature pressure, but has no effect on oil pressure when hot.

- I check the gap between the oil pump cover and the gear, below 0.1mm. I decided though to change the pump for a new one from Aeroconversion. No effect.

- Valves clearances were checked. OK.

- I ended-up dismantling the engine to check the wearing condition of all lubricated bearings, pushers, rockers, etc.... After a long day of carefull measuring, I can conclude that all parts in the lubrication circuit are well within the documented wearing limits (actually within the original manufacturing tolerance for most of the parts).

- I inspected the case to look for cracks. No crack discovered.

- The only abnormal findings:
1/ The rear back cylinder has severe wearing traces on the side, the top segment is broken. Most probably an overheated cylinder, but I don't see how this could affect the oil pressure. The two rear cylinder head studs on this cylinder where found not tighten (nut just in contact with the head, but almost no torque needed to unscrew those two). I am wondering if this could increase the valve clearance when the engine is hot, and degrade the tighness of the oil circuit between the pushrods and the rockers ???

2/ The front bearing of the camshaft had flanges only on one side. The other side had no flange, just like the two other bearings. I don't think this has any effect on oil leakage, (as the other bearings of the camshaft have no flange).


This issue is really driving me crazy, so if anyone had similar symptoms, or if you have suggestions, please let me know!!

Many thanks for your help!!

[pappas]

Do I have to ask if you have oil leaks with your Aerovee? Mine always did. Too much crankcase pressure can blow oil overboard, past seals, and past the prop hub slinger.

I had very similar symptoms with the Aerovee Turbo on my last Waiex. I checked all of the things you mentioned in your post. My in-flight oil pressure did not drop to 15 psi but was mostly around 25-30. Kerry told me that 30 psi in cruise was OK. However, I was never happy with it. I found a slightly burned #3 exhaust valve and decided to replace the MOFOCO heads with the EMPI's that Sonex now provides. A friend ported the heads for me, did a 3-angle valve job, and we installed new pistons and rings.

The result was that the compression was significantly increased and the oil pressure finally ran in the 50-60 psi range recommended in the manual. Do a hot compression check and see if you have any problems there. Hopefully, it turns out to be something simpler. Good luck!

[kmacht]

Since you checked the most common things, without seeing your setup I would be inclined to think it is something with your full flow system but it’s hard to tell. Can you describe the full flow/filter/cooler setup and routing? Did you upsize the pump for the added flow? Did you block off where the pump normally exits into the case when you installed the full flow system? I’m assuming you removed the plug and tapped the correct port on the front of the case for the return? How about fit of the pump to the case? Was it a tight fit? When you bought the new cover to put full flow in did you check for clearance between the pump cover and the gears inside and make sure the cover was truely flat?

Keith
#554

[Renaud]

Many thanks for your review and advices!

Pappas, I did not suspect the heads for the oil pressure issue but based on your experience maybe I should. I may decide to change them, they're not in perfect conditions. And no abnormal external oil leakage on mine.

Keith, maybe I wrongly called it "full flow", it is just the bottom mounted set-up, as described in the Aerovee manual (enclosed picture). The two hoses from/to the cooler connects to the pump cover, no return to the crank case. All the flow from the pump constantly flows through the cooler and is then injected normally in the case through the pump body. I did check the new pump clearance between gears and cover, and that the cover was trully flat. The pump fits very tight in the case.

[Area 51%]

When you did the sending unit test with compressed air, did you heat the sending unit up to normal oil temperatures?
I never trust anything electrical. I wouldn't call the coroner till a purely mechanical gauge was tried. .

[Renaud]

That's one of my next tests: testing the gauge at high temperature (using a hot air gun to heat it up). But i have the same problem with two different pressure senders...
And yes, maybe setting up a mechanical pressure to the cockpit...

Updated post: test just done , no noticeable difference in sender resistance value between ambiant and running engine temperature (test done at 45 PSI/ 3 bars).
Still searching...