No Oil Pressure

[jatkins]

I took off from my home airport the other day, when I was approx 8 miles away I see my oil pressure
is now at zero, ....I turn around and start back , oil temp is normal, I reduce power to 2300 rpm,
CHT and EGT are all normal on all 6 cylinders. I make it back and land ok.
Oil temp stayed constant.

After shut down, no oil leak, and 6 qts on the dipstick.

We dissconnect the oil pressure line at the fire wall , and connect it to a calibrated guage,
still zero oil pressure.
We take off the oil pressure line, blow it out, re-install it, and still zero pressure.
We take the line right off , run the engine and just a small amount of oil comes out slowly.
( now I am getting very very worried !!! )
We pull the oil pressure relief valve, clean it up, with some scotch bright, re-install, still zreo pressure.

Next we dump the oil, ( clean ) and cut open the filter. ( The engine has 18 hours on it since we changed the sump )
We find approx 25 specks of continental paint chips, about the size of a pin head.Also we find a small amount of
magnetic metal, which the mechanic feels is from a exhaust guide most likely, or possibly a pump gear. The
metal was quite fine and the total amount would cover the small magnetic about the size of a pencil eraser.

Our plan on Monday is to pull rocker covers to look for a possible bad exhaust guide, and also to recheck
the oil pressure relief valve, as I did not check the seat area of the plunger, first time.

Any suggestions ? Any experience with oil pressure falling to zero ?
My engine ( O-300D ) has 550 hours on it in 4 years, and the oil pressure has always been 40 psi.

One person mentioned to me that if the oil pump quite, the oil temp would not go up as the hot oil
would not be circulated to the temperature bulb. Is this the case ??


I have my fingers crossed John

[Bruce Fenstermacher]

It would be nearly impossible for your oil pump to quit without the accessory case blowing off the engine. Make sure the relief plunger seat is clean. Pull the nipple out of the engine that the oil line connects to and make sure it is clear. It should be a very small hole which acts as a restriction so if your oil line breaks you oil doesn't dump overboard in a second but rather takes a few minutes. This hole could have gotten clogged.

[FredMa]

You didn't say what section of the line you removed and blew out. between the firewall and gauge or firewall to engine. I had the same problem once and also had to clean out the line. I believe I had to run the engine and crack the line at the gauge and allow the air to escape before my gauge would work.

[53B]

Does the tach work? It is driven off of the oil pump gears. If the tach works, the pump is at least turning. Hope this helps!

[jatkins]

We took off the oil pressure line, between the engine and the fire wall.
we did not , crack / bleed the line, but we ran the engine with the line diiscoonected,
and no oil came out.

Yes the tach is still working, as is the alternator, and mags.

[Bruce Fenstermacher]

we ran the engine with the line diiscoonected,
and no oil came out.

In my mind there are only 3 likely causes, of course there could be others. No oil in the engine. Relief valve is held open. The restrictive adapter is clogged.

You have looked at two, I'd look at the adapter then the plunger seat before going further.

[jatkins]

Thanks Bruce,
That will be number one on my list today, after work.
I am going to pull the finger screens at the back ( bottom) of the rear case
while I am at it.

I need to get my confidence back on this engine.

[DWood]

You might try priming the pump by removing the line and pushing oil down into the pump. You can use a hand pressure pump and hose to a fitting. If this works, then will need to figure out why it leaked down.

[GAHorn]

there is some good advice and there's some bad so far.

pull the fitting off the side of the engine, and run the engine
you should see oil streaming down the side of the engine when it is running.

if not then blow air backwards into that fitting hole to clear the passages
then try running it again.

[jatkins]

I did both of these items,....... still no flow.
Next we put 4 washers in the oil pressure relieve, still no flow.

We then completely removed the oil pressure relief valve assembly, and had lots of oil flow
out of the oil relief valve hole.

[FredMa]

lots of flow from the pressure relief valve means that the pump is working and the engine was most likely not starved of oil. Sounds like your restrictor is hopelessly clogged with some sort of debris despite your attempts to blow it out. Have you tried fine wire to open the hole up? can you remove the restrictor, if so remove it clean it and make sure you can see light through the hole.

[GAHorn]

I failed to point out that your mechanic must not be familiar with these things,......
as valve guides are NOT magnetic.

[jatkins]

Last night I pulled the oil screen, ( beside the oil filter ) inside the screen, was a piece of shop paper towel, a piece 1/3 of a sheet.
We have no idea how this got into the sump ???
We put the oil back in and ran the engine , oil pressure came back up to 40 psi, and stayed there at 1800 RPM, and again at idle, 600 rpm.

My intention is to pull the oil filter again after 5 hours.

Lesson learned,... always pull the screen, every time you pull the filter.