Erratic Oil PSI Reading

[Downeast25]

I am getting used to my new to me 2007 DA40 XL I picked up last week. I posted earlier that I was concerned I was burning oil. After hearing from the forum, speaking with my mechanic and CFI, we decided I was just filling beyond the "happy place" of the engine. With that in mind, I took off yesterday from U77 to KHND, a two hour flight roughly. As I was approaching Vegas I noticed an erratic PSI reading. The gauge would never settle in at a constant reading and it bounced between the green and yellow with a range of a few PSI. The whole time, the oil temp was very solid at 188 and not a problem. I also feel the prop lever was not as quick to respond to inputs. After I got on the ground, I was late for my appointment and I forgot to check the level of the engine oil. I suspect it will be low. I launched with just below 5 quarts. The plane did just come out of an annual and all compressions were great. Please comment...

[rwtucker]

From my experience Bill, erratic OP is a definite concern. The fact of genuine low pressure cf. a problem with the gauge is suggested by the unresponsive prop control. My OP is always stable and as expected under various conditions. It would help to know if you threw oil after flying with ~5 quarts. If you did not, the low pressure indication could be bearings. If you did throw oil, the low pressure could have been due to inadequate oil volume, which you would be more likely to see in turns, etc. You might have both problems. Bummer for any of these possibilities.

On compressions. Did you test them since purchasing the aircraft? Have you had your A&P look at the gaskets and other parts for indications that the engine might have been severely overheated? This is just another line of inquiry, of many.

[ricksigler]

Mine does that if I get to about 4 1/2 quarts, but only in the bumps. As soon as I add a quart - steady pressure.

Rick

[Downeast25]

Here is the follow up:
I checked the oil the next day and sure enough it was at the bottom of the dipstick. I am for sure burning/losing oil. I can see it on the underside of the plane so I think it is coming out of the breather tube instead of burning off. That also agrees I think with very solid compressions coming out of the annual a month ago.

Before the 2 hour flight home I added two quarts and left with 5.25 on the dipstick. I watched it like a hawk and stayed over airports from KHND from U77. The OP was solid but I did find the prop lever not immediately responsive, especially climbing. Otherwise all indications were great. Upon landing I checked the oil again and it reads 4.5.

I suspect the governor to be the problem but I am no A&P. I am going to have it inspected today.

[Downeast25]

New update...

I spoke with my A&P this morning. He says he is 98% sure it is oil leaking past the piston rings. He is going to have a better look tomorrow. This does not sound like good news to me on a plane I took delivery on a week and a half ago.

[rwtucker]

Anything is possible and you want to give a seller the benefit of the doubt. This said, it is likely that the seller was aware of this problem and may have caused it. If so, this is not the norm. Pilots I know are obsessive about making sure everything is in order before selling their aircraft.

If rings are the problem, what were the compression readings that you or your mechanic took and in what condition are your lower plugs? If it should turn out that the seller lied about compression readings, you may have a basis for going back to the mechanic of record and the seller.

[Downeast25]

It literally just came out of the annual which I paid for of course to have an extra thorough pre buy. Compressions were great according to the shop. Prior owner says he never leaked or burned excessive oil. It's a head scratcher to him. Either that is not totally true or something happened during the annual.