My 182 has an O-470-L. The oil pressure at startup registers just at the bottom of the green, roughly 30 psi. By the time it gets warm it drops back to 10-15psi and will stay there with minimal change throughout MP/RPM settings. Although my engine has higher calendar time, it only has 300 since a no name overhaul. My last two oil changes haven’t shown any metal and my temps aren’t out of the ordinary. I’m running Aeroshell 20/50. We have hooked a secondary pressure gauge into the system to confirm it isn’t the sending unit or gauge itself. We also blew out the line to the sending unit to ensure no debris. The case and engine compartment are dry and overall it doesn’t burn much oil, maybe a quart every 6 hrs.

Any insights as to what might be causing this or what we can do to remedy the issue?

Pressure relief valve may have something keeping it open...thus oil starts running through the cooler before it ever warms up....like a bad thermostat on a car....the water warms but never gets to operating temps...how’s the CHT during this....

Gotcha. Makes sense, esp if it only builds pressure when the oil is cold right at startup. CHTs are normal. My engine has never run hot. If it wasn’t getting oil you would think you would see a spike in the temps.

It's a PITA with the 0-470 in the 182, but you can barely access the relief valve which is located on the back of your engine. Might be easier to gain access by removing the alternator. Sometimes a small nugget can get stuck in there and hold the relieve valve open just a bit. If thats the problem, you might want to have the nugget analyzed.

I went through this with mine. I imagine you have the electric gauge? More than likely you have the non - adjustable relief also- Under a cap there is a ball and spring. Assess able from the bottom Crud, weak spring or even a non - round ball. I replaced the ball and spring with new on mine - no real change. Found my electric sensor dented and a loose stud - replaced it and it slightly improved pressure, using a manual test guage we found the old dash guage consistently reads about 10 lbs low. With cold oil my guage reads about 55lbs at run up, 40 at idle. Hot oil 25lbs at idle, just over 30 at cruise. Once hot is never leaves the very bottom of the green, no matter the rpm.

Start with getting your mechanic to test your pressure with a manual test guage to see if it is an actual pressure issue or is it just a indication issue.

Mark Y. wrote:…. More than likely you have the non - adjustable relief also- Under a cap there is a ball and spring. Assess able from the bottom …..

My 470K has an adjustable relief valve.
Screw & lock nut, in an awkward location on the bottom aft corner of the engine.
Yours might just need tweaking.

Just read that you did actually confirm the low pressure with a gauge. Definitely look into this deeper, that is pretty low. Idle hot low spec is 10 psi. Cruise rpm low spec is 30 psi If you are only get 15 lbs at run up speeds with a good gauge I would be checking the relief before any further flying. If not the relief - worn oil pump or loose bearings. I am kind of amazed your mechanic hasn't gone after the relief right away after confirming the low pressure. Really your oil pressure is out of spec - so isn't airworthy. Waiting for CHT's to rise is just as bad as waiting for your filter to fill with metal - at that point it is too late.


Here is a link for a free manual for you 470 L https://www.southernairboat.com/pdf/air ... M_MO-2.pdf

Had very similar symptoms on a O-300. Checked the pressure relief for debris and none found. Added a temporary washer under spring and pressure went right back up to normal at all oil temps. Ordered a new relief spring and has been perfect for the last 50 hours or so.

+1 for checking the relief valve. If nothing is found then ask you mechanic about adding a washer under the spring and keep checking the filter for metal.

Thanks for the replies guys. Y’all bring up some good points.

Mark Y. wrote:Just read that you did actually confirm the low pressure with a gauge. Definitely look into this deeper, that is pretty low. Idle hot low spec is 10 psi. Cruise rpm low spec is 30 psi If you are only get 15 lbs at run up speeds with a good gauge I would be checking the relief before any further flying. If not the relief - worn oil pump or loose bearings. I am kind of amazed your mechanic hasn't gone after the relief right away after confirming the low pressure. Really your oil pressure is out of spec - so isn't airworthy. Waiting for CHT's to rise is just as bad as waiting for your filter to fill with metal - at that point it is too late.


Here is a link for a free manual for you 470 L https://www.southernairboat.com/pdf/air ... M_MO-2.pdf

When my mechanic hooked the new pressure gauge up he said that my pressures were just barely within tolerances, so legally I’m still airworthy; however, by no means do I plan on doing any flying until we get this issue figured out. What I described above were what I witnessed with the basic panel gauge. The one he used was more exact. We did discuss the relief valve on Friday but he didn’t have time to dig in then. I’m hoping that’s all it is and not an indication of something more catastrophic.

Either way, I’m learning a lot and making my old airplane better. While we were looking into this, we also discovered some other minor issues like a bad flapper in my airbox, some cracking in my baffling (I think that’s what it’s called) and a small hole in my ducting. I’m really glad I spent that money on a good pre-buy.

Nushi wrote:…..I’m really glad I spent that money on a good pre-buy.

IMHO you can't expect a pre-buy or even an annual to catch absolutely everything.
How many times have any of you guys found an older-than-a-year issue during an annual inspection?
You can expect your first annual to have some surprises.
Most people I know expect it to take at least a couple years to drive out the voodoo from the previous owner(s).

Nushi wrote:While we were looking into this, we also discovered some other minor issues like a bad flapper in my airbox, some cracking in my baffling (I think that’s what it’s called) and a small hole in my ducting.

Are we still talking about the airplane? This sounds like the same problems AKGreg had during his last medical.

Well there wouldn't be a minimum if it wasn't good enough. Good pilots tend to be slightly OCD (Obsessive Compulsive Behavior). So we want everything to be in the middle. You can replace the spring and ball, nothing hurt by this. You may want to inspect the seat the ball sits in. Occasionally, you may need to lap the seat with some compound using the old ball. The balls are really cheap, under $10 as are the springs. Sometimes the oil pump itself is getting on. It rather depends on the gap between the gears and case aside from wear on the teeth of the pump gears themselves. Wear is a fact of life on this system. To the point, with a stock spring and newish ball it may not be regulating to the middle of the pressure range. The OH manual allows for washers to increase the pressure to adjust it to spec. I seem to recall, up to three washers can be used. You can most likely get the OH manual in PDF form on the web somewhere, to give you the allowable number of washers. Each washer gives you approximately 5 psi change of pressure.

No idea on how far along your engine is in hours, bearing wear may be creeping in. You may also want to switch to Aeroshell 100. Multigrades are great when it is unpleasantly cold, but straight 100 may give you slightly better pressure as well. Just preheat your engine if it is in cold environment.

On a small note, there is a restrictor in the in the line to the gauge. This way if the line breaks, it only allows a small quantity of oil to squirt out at a time. So ensure it is still there. These lines do break. Mine broke on my L-19 once and I suddenly had hot oil squirting on my right foot, very unpleasant. To make it worse, my vacuum gauges started to fill up with oil. Seems the leak was just over the vacuum filter. So it went from a Land Now, cheap fix. To OMG, I have to overhaul the ADI and DG as well. So when you are on a jag to replace all those ratty lines, don't forget the segment from the firewall to the gauge. MAKE SURE THE RESTRICTOR IS STILL THERE.

Guys, thanks for all the replies. We got this figured out, thankfully, without too much agony. Long story short, we started with an oil change, inspected the filter and found nothing. We refilled with Aeroshell 100. No difference. The mechanic pulled the relief valve and there was a tiny tiny fleck of aluminum caught right on the seat keeping the valve from fully closing. The valve was pulled out, polished and reset and the oil pressure popped back up to the top of green. The fleck was mildly concerning but since there’s been no signs of metal noted in my last two oil changes, I’m hoping it was just a fluke, who knows. I will keep an eye on it. Nonetheless, it’s good to have my old girl back.

dogpilot wrote:On a small note, there is a restrictor in the in the line to the gauge. This way if the line breaks, it only allows a small quantity of oil to squirt out at a time. So ensure it is still there. These lines do break. Mine broke on my L-19 once and I suddenly had hot oil squirting on my right foot, very unpleasant. To make it worse, my vacuum gauges started to fill up with oil. Seems the leak was just over the vacuum filter. So it went from a Land Now, cheap fix. To OMG, I have to overhaul the ADI and DG as well. So when you are on a jag to replace all those ratty lines, don't forget the segment from the firewall to the gauge. MAKE SURE THE RESTRICTOR IS STILL THERE.

This is a very good point. Also, check the oil pressure line from the firewall to the engine. That line should be a flexible line. I have now owned three airplanes that had solid lines there. So, one end of a solid copper line affixed to the firewall, other end connected to engine.....which moves. My first one, the line broke and hosed oil all over. Landed on a river, crimped the line and flew home. The line had a loop in it, presumably to prevent it from breaking. Mechanics said should be a flexible line. Fixed it, and the next two.

Make sure yours is a flex line.

MTV