Low Oil Pressure

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Low Oil Pressure

Postby IP076 » Fri Jul 09, 2021 12:31 am

Starting to troubleshoot a seemingly low oil pressure.

I've started to see a low oil pressure indication since my last oil change (June 2, 21, Tach 2692.75), see the pic below:

IMG_1935.jpg


Two things of note occurred at the point of last oil change, I replaced the ADC oil screen and summer hit Spokane, with temps in the mid-90s to a high of 108.

Historically the gauge sat about 30-35psi in cruise. I had been using Phillips 20w50. It was suggested to try running a straight 50w (Aeroshell W100) during the summer up here, so I did an early oil change today (Tach 2699.05) and took it for a test flight and snapped the above picture. Not much improvement.

I've read the following thread: viewtopic.php?f=2&t=8726

I know a lot of people have continentals that run on the low side for oil pressure, so before I go tearing into more troubleshooting I thought I'd see what most thought. Is it typical to see those low of oil pressures during summers with excessive temps? Or is the engine with nearly 1600 hours since a decades old overhaul trying to tell me something more important?

As always, thanks for the info!
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Re: Low Oil Pressure

Postby GAHorn » Fri Jul 09, 2021 3:13 am

The first thing to consider is the accuracy of your gauges before you go into corrective actions. At what RPM was this photo taken?

The oil temp shown in your photo (if accurate) is not excessive…. so low oil pressure should not result from oil temps in that range.

The oil pressure relief valve will be an early consideration. The valve seat and the spring pressures should be checked. (That data is posted in another thread, I’ll try to find a link for you.)

I once performed a “down and dirty” test of my own oil pressure gauge by using plumbing fittings and hooked the gauge up to my gas welding regulator…. they both agreed at 50 psi so I considered it “good enough” but if you have no other method you might send it in to an instrument shop or just replace it. (the range of the gauge you have is so large I don’t think it’s very sensitive…but that’s just my preference to have a small range/scale….. my gauge range is 0-60…. and my 1000 hour engine consistently runs 50-55 psi at cruise using SAE 50 oil regardless of oil temp. I wouldn’t let 1600 hours worry me. Nor would I let 20 psi worry me if you’re not running 2000+ RPM. If you’re showing 20 psi at idle with that oil temp of 190 or so…. you don’t have a problem.
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Re: Low Oil Pressure

Postby n2582d » Fri Jul 09, 2021 3:46 am

GAHorn wrote: ... At what RPM was this photo taken? ...
Screen Shot 2021-07-08 at 8.43.42 PM.png
Screen Shot 2021-07-08 at 8.43.42 PM.png (42.5 KiB) Viewed 966 times
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Re: Low Oil Pressure

Postby IP076 » Fri Jul 09, 2021 4:50 am

George,

Thanks for the input. That pic was at cruise RPM of 2300-2400, which is why I’m a little concerned.

My next troubleshooting step is to verify the gauge and then the pressure relief valve.

Thanks for the input.
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Re: Low Oil Pressure

Postby bat443 » Fri Jul 09, 2021 5:27 am

Just as a safety note to anyone reading this thread, oil and welding oxygen do not mix, could cause an explosion, hence the warning on the oxygen pressure gauge that says "use no oil". If I was going to use a gauge set available to me I would use shop air and a differential compression tester where the 2 gauges are often checked against each other to establish some degree of accuracy.

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Re: Low Oil Pressure

Postby Bruce Fenstermacher » Fri Jul 09, 2021 9:57 am

Going from 30-35 range to 20 just like that makes me think, what just happened. I would not be concerned at all with the type of oil you changed to ie 100W from 20w-50, if anything this might actually raise your oil pressure. I'd be looking at the ADC screen. Is it installed correctly?

Of course the gauge could be faulty. What is your idle oil pressure indication?
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Re: Low Oil Pressure

Postby GAHorn » Fri Jul 09, 2021 11:20 am

bat443 wrote:Just as a safety note to anyone reading this thread, oil and welding oxygen do not mix, could cause an explosion, hence the warning on the oxygen pressure gauge that says "use no oil". If I was going to use a gauge set available to me I would use shop air and a differential compression tester where the 2 gauges are often checked against each other to establish some degree of accuracy.

Tim


Thanks Tim…. Excellent advice. I should have stipulated that I used my ARGON (C25) welding bottle for that pressure test. :lol:

For some reason the FIRST photo depicted in the original post did not include the tach-pointer area…. and is why I inquired of the RPM. I see that photo has been re-uploaded.
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Re: Low Oil Pressure

Postby IP076 » Fri Jul 09, 2021 11:57 am

Bruce,

The change in oil was an attempt to see if it boosted the oil pressure, it did not.

The idle oil pressure is 50-ish cold. After a 20 min flight on the ground at idle it’s not even reading, or it’s barely off the lower stop. I will say this airplane has always had an indication between 5-10 at warm idle.

My initial thought was the ADC screen, as that seems to be the obvious thing that changed. The screen I removed has a chewed up outer seal but I still have it. I guess I can put it back in place and run it and see if it returns to normal.

I wouldn’t be surprised if it’s in fact the gauge either. I have a new CGR-30P awaiting install but my avionics shop ran into some issues with the EGT sensors and clearance with the intakes, a whole other issue I need to dig into.
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Re: Low Oil Pressure

Postby lowNslow » Fri Jul 09, 2021 3:36 pm

GAHorn wrote:The first thing to consider is the accuracy of your gauges before you go into corrective actions. At what RPM was this photo taken?

Guess you didn't see the tach in the picture? :wink:
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Re: Low Oil Pressure

Postby daedaluscan » Fri Jul 09, 2021 3:42 pm

I would check the pressure relief valve. I had two instances where a small piece of carbon was lodged under the valve seat. Low oil pressure fixed immediately I removed it. My O_300 ran at 30 idle, close to the redline all the time at RPM, at any temperature, for the 1000+ hrs I ran it. It had 2000 hrs SMOH when I removed it
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Re: Low Oil Pressure

Postby GAHorn » Fri Jul 09, 2021 5:49 pm

lowNslow wrote:
GAHorn wrote:The first thing to consider is the accuracy of your gauges before you go into corrective actions. At what RPM was this photo taken?

Guess you didn't see the tach in the picture? :wink:


Previously posted:
GAHorn wrote:…..

For some reason the FIRST photo depicted in the original post did not include the tach-pointer area…. and is why I inquired of the RPM. I see that photo has been re-uploaded.


Check the oil pressure relief valve for cleanliness and condition.

The current production spring is Blue in color.

The oil pressure relief spring should be compressed to 1.56 inches and the pressure should be 6.06 to 6.31 lbs if new, and 5.75 lbs minimum if used.
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Re: Low Oil Pressure

Postby Bruce Fenstermacher » Sat Jul 10, 2021 1:08 am

Oh boy. I'd be checking that gauge quick. Let us consider it is correct. 8O. If so and it is being caused by an open relief, your bearings are still not seeing enough pressure. I recall a minimum of 10 required at idle. And your bearings will soon be shot if they aren't already.

While others might have had a open relief valve, I was not that lucky. It was my bearings and even putting in a second oil pressure gauge and "check" the original, cleaning and replacing the plugger and spring, the pressure was still low and it was my bearings.
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Re: Low Oil Pressure

Postby GAHorn » Sat Jul 10, 2021 3:03 am

I have another point of view relative to Bruce’s opinion. If there’s any oil pressure AT ALL… say 5 psi…then the bearings will be fine. It’s only necessary that oil be present to prevent dry bearings to lubricate and cool them. This is based upon what i’ve been taught at automotive and aircraft engine tech schools.

I also have a real-life experience in this matter.

Example: I was cruising at 11K’ in a C-414 when the left oil pressure suddenly dropped to only 5 psi. It ran there for at least ten minutes while I decided what to do about it…..and it may have run as long as 20 minutes because that’s when I wrote down the cruise parameters I traditionally keep.
I feathered that engine and landed and called Ram Aircraft Engines in Waco, Tx (it was a Ram conversion). Their chief engineer wanted to know if the prop ever indicated any kind of “surge” or RPM excursion…. and it hadn’t and I told him so.

He said that if the RPM didn’t waver then the core engine was unharmed and to search for issues such as oil pressure relief or oil filter by-pass issues.

We found some chunks of “pink plastic” beneath the oil pressure relief valve-seat and inside the spin-on filter…..and cleaned out the relief valve…changed the oil and filter…. ran the engine for about 20 minutes to “flush it”…then changed the oil and filter again.

It turned out that AeroShell issued an AD note that their production facility suffered a pump-failure that released plastic into the oil and the AD was applicable to a certain LOT of oil…which the maintenance facility who maintained the airplane had ignored.

That engine was not hurt by the event…. and the Ram engineer convinced me that as long as RPM variations do not occur and as long as a minimum of 5 psi is maintained that the engine crank and cam and conn-rod bearings are not injured.

In THIS discussion-thread…we are observing about 20 psi oil pressure…. Clearly sufficient to prevent damage, IMO.

YMMV
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Re: Low Oil Pressure

Postby IP076 » Sat Jul 10, 2021 4:32 am

Guys,

Thanks for the info. Airplane definitely isn’t going anywhere until this gets worked out.

As much as I want to go out tomorrow and pull the pressure relief valve and inspect it, might be time to get an A&P out to help get things straightened out.
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Re: Low Oil Pressure

Postby hilltop170 » Sat Jul 10, 2021 6:51 pm

I second removing the pressure relief valve and making sure it is clean and not hung open.
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