Low Oil Pressure

How to keep the Cessna 170 flying and airworthy.

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Re: Low Oil Pressure

Postby GAHorn » Sun Aug 01, 2021 4:32 pm

cessna170bdriver wrote:
GAHorn wrote:I’ve seen two pressure transducers leak over the years in various installations. There’s a diaphragm inside that can eventually fail and they leaked thru the phenolic/base seal. (tho’ it was only messy… didn’t dump the oil overboard.)

Only two (in how many years?); that’s a much better record than the copper line.


They were the only ones I was aware of being installed and were discovered while looking for the oil leaks. :lol:
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Re: Low Oil Pressure

Postby IP076 » Wed Aug 04, 2021 10:35 pm

George,

Last Thursday I took your advice and warmed the airplane up in the pattern. I don't recall for sure, but the air temp was somewhere in the upper 70s. Here's a few pics:


Initial Engine Runup at 1700 RPM:
IMG_2071.jpg


Climbout at 2500 RPM:
IMG_2072.jpg


Downwind descending:
IMG_2073.jpg


Taxiing:
IMG_2074.jpg


Climbout at 2500 RPM, second pattern:
IMG_2075.jpg


More pics in subsequent post.
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Re: Low Oil Pressure

Postby IP076 » Wed Aug 04, 2021 10:42 pm

Continued:

Taxiing in again:
IMG_2076.jpg


Climbout again:
IMG_2077.jpg


On downwind:
IMG_2078.jpg


Taxiing in, final time:
IMG_2079.jpg


That last picture taxiing in shows the oil pressure basically at the stop, with about 195-200 degree temperature. Even at the upper RPMs, 2500 or better, it doesn't seem to make 30psi.

I had to leave town due to an emergency. When I get back I'll be (finally) replacing the gauge to check it's accuracy. After that, I'll yank the screen and look for anything new. Apparently the postal service delivered my oil sample via carrier pigeon. Last I checked Blackstone didn't have it yet, I'll call again tomorrow.

If there's nothing obvious after that, I'd have to guess it's the oil pump or bearings...I'd assume I'd see that in the oil, but otherwise not sure how to verify such.

Anyways, thanks again to the forum members for continued help.
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Re: Low Oil Pressure

Postby GAHorn » Thu Aug 05, 2021 2:52 am

While those readings are concerning…. until we know the gauge is accurate….we don’t know much. (Hoping that gauge is wrong.)
'53 B-model N146YS SN:25713
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Re: Low Oil Pressure

Postby IP076 » Thu Aug 05, 2021 3:50 am

GAHorn wrote:While those readings are concerning…. until we know the gauge is accurate….we don’t know much. (Hoping that gauge is wrong.)


You and me both. I should be back in town next week and plan on hooking a different gauge up to verify. I’ll let you know what comes of that.
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Re: Low Oil Pressure

Postby Bruce Fenstermacher » Thu Aug 05, 2021 9:48 am

One encouraging thing is that looking at your temp gauge, the readings look normal. Maybe you know different ie your have lower, the same ,or higher oil temps given conditons.

When I wiped out my bearings, oil temperature climbed to near over temp conditions and that is a lot considering the Cub oil temp never got over 140°.
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Re: Low Oil Pressure

Postby c170b53 » Fri Aug 06, 2021 2:43 am

Looks like you’re only using one half of that oil gauge if that, maybe a new lower range gauge might work better for you.
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Re: Low Oil Pressure

Postby IP076 » Tue Aug 24, 2021 11:34 pm

Hey guys, been away from the airplane for work and life stuff for a month or so, unfortunately.

I did make it back to this project today, so here's the latest. I did get the oil analysis back, nothing out of the ordinary, good comments, no evidence of any metal being made. I did check the screen again today, no metal...hasn't been run much, but figured I'd check it.

I hooked the existing oil pressure gauge up to the air compressor, which has a gauge on the regulator and a secondary pressure gauge I had connected to it. I compared each at 20, 30, 40, 50, and 60 psi.

Here's some pics:

20 PSI @ Compressor:

IMG_2212.jpg


20 PSI @ Gauge:

IMG_2213.jpg


30 PSI @ Compressor:

IMG_2214.jpg


30 PSI @ Gauge:

IMG_2215.jpg


40 PSI @ Compressor:

IMG_2216.jpg


Continued in next post...
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Re: Low Oil Pressure

Postby IP076 » Tue Aug 24, 2021 11:42 pm

Continued from above:

40 PSI @ Gauge:

IMG_2217.jpg


50 PSI @ Compressor:

IMG_2218.jpg


50 PSI @ Gauge:

IMG_2219.jpg


60 PSI @ Compressor:

IMG_2220.jpg


60 PSI @ Gauge:

IMG_2221.jpg


As you can see in the lower PSI pics, the margin of error is around 10 PSI and shrinks to maybe 4-5 PSI at the higher end. All of this assumes that the two gauges on the compressor end are fairly accurate of course.

Interesting find. I ordered a replacement gauge, figured it was worth a shot. As mentioned above, I got one that didn't go as high...seems excessive to have a scale to 120 PSI in this installation.

Thanks again for your help in diagnosing the issues here.
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