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High Oil Pressure causes

RVG8tor

Well Known Member
Along about my 50th hour my plane started to have high oil pressure on the first flight of the day. The first time happened on takeoff, I went around the pattern and landed. I took the cowling off and looked over things and suspected a bad sender, I still had the Dynon single wire sender. Suspecting the sender I went and flew and not alarms.

I had already bought the newer 3 wire sender when I had a pad fuel pressure sender out of the box and learned Dynon no longer carries the old one wire sender. The next day I changed to the new sender then all was good for the next flight and a couple after that. Then it came back initially it would be on the first flight of the day and I would get it during takeoff, I learned to ignore it a while and it would go away eventually, I never get it on the second flight after a fuel stop.

Now I get the high pressure alarm on the ground, it pegs high or nearly so and then drops fast to normal the climbs, last flight after sitting for 2 weeks I flew for 15 minutes before it settled down to normal.

This morning after a week off it gave it to me on the run up but was normal by the time I took off.

I warm the oil before flight, usually it is 80 plus degrees. But I have flow once or twice when away from home and can't see a correlation on this one.
I have checked the wires and all are good, but I did not ohm check anything, since I don't know what numbers I should see.

It was fine the first 50 hours, perhaps something happened in the oil change, I did remove and check the oil screen on the first couple oil changes. Last time was 7 hours ago, this was at 90 hours, I can't believe I have flown this much since December!

Consumption is good, 7 hours and only down a half quart since the last oil change.

Inflight after it settles down I have 80 psi and 180 degrees for oil parameters.

Flew today and after the run up all was good for two hops.

If anyone has any ideas I would really appreciate any help.
 
What is the value. High is subjective. I start at north of 100 psi but settles to
95 or so in cruise, More is better
YMMV
 
My values are the same as Stripes are indicating...100 plus on TO and climb, 90 or so in cruise. Pressure is only on the stuff that needs it, and isn't going to blow seals, as they are all on the vented side of the crankcase.
 
Pressure

On another brand, pressures will run high if you have a faulty ground connection. Check ground connections at the EFIS itself and sometimes anodized aluminum threads on the sending units don't make good grounds where they screw in.

intermittent ground connections can cause intermittent false high readings. If you can't find anything, try a plain old analog pressure guage to double check pressures.
 
Pressure Pegs

The pressure pegs the gauge most of the time, which is set with a high of 145 but I can see it move up from normal to the high, this only takes a second or two.

It looked like a wiring problem but I have not found anything wrong and this is all new parts so there has been not time for corrosion to set in.

Not sure why this would only happen with the first flight of the day if it were a wiring issue.
 
I have been told my a long time A&P that high oil pressure is worse than being a little on the low side. This is due to excessive wear from the high
pressure oil on the bearing surfaces. Lycoming gives a recommended max
oil pressure and makes no mention that more is better. I think something
around 80psi is recommended. I guess his theory is like the water jet principle where high pressure water can cut
1/2 inch steel. Experts please correct me if this is incorrect.

JM
 
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not a water jet !

If you look at the oil pressure path, the bearings and valve train get the direct pressure, all else is basically splash. There is no direct pressure to a seal or gasket. The most vulnerable component is the oil cooler and lines. The comparison to water jet similarity is apples/oranges, as the water jet uses water at several thousand psi, with a slurry of abrasive such as steel or other grit...the water just carries the cutting media. I am not an expert by any means, but like my pressures on the high side...always like hearing from true engine gurus that may chime in.
 
I like high oil pressure. A typical waterjet pump takes a 50hp electric motor to run the pump and the pressures are in excess of 50K psi. Bearing erosion is not a concern in a slow revving motor like a Lycoming.
 
If you look at the oil pressure path, the bearings and valve train get the direct pressure, all else is basically splash. There is no direct pressure to a seal or gasket. The most vulnerable component is the oil cooler and lines. The comparison to water jet similarity is apples/oranges, as the water jet uses water at several thousand psi, with a slurry of abrasive such as steel or other grit...the water just carries the cutting media. I am not an expert by any means, but like my pressures on the high side...always like hearing from true engine gurus that may chime in.

I wasn't trying to make a direct correlation to a water jet cutting machine. I would have to wonder why Lycoming gives us a way to minutely adjust oil
pressure instead of just taking the max the oil pump can give?
 
I would have to wonder why Lycoming gives us a way to minutely adjust oil
pressure instead of just taking the max the oil pump can give?

Because they are old-school and only make mediocre improvements to anything. All it takes is a longer housing and a longer screw to get more adjustment range.
 
Rocket Bob
You may be right. I certainly can't dispute your logic. I was just relaying what a long time aircraft engine rebuilder told me. I definitely used a bad
example for the concept-water jet. The Colorado river and the ditch it created would have been a better example. I have a call in to Lycoming on another issue and will ask them their opinion. I still feel you can't go wrong
sticking with the Lycoming published oil pressure ranges.

Thanks
Jim Miller
 
Is this on a Lycoming? I had high oil pressure once on an O-320. After much worrying over it, I determined that there is almost no way to get high oil pressure on a Lyc other than cold temps or thick oil. There is a relief ball that relieves pressure. It is almost foolproof. It is most likely a gauge problem. I would look for a bad sender or ground loop in the wiring of the sender.
 
Kent
I agree. We just got off on a tangent debating the merits of setting oil pressure higher than Lycoming recommends. This can be done by cranking up the pressure setting on the adjustable type. I wish someone would explain the rationale for higher oil pressure. What does the higher than
recommended pressure do for the engine? I have an interest in this because my oil pressure on my 0235 is a little low-about 71. I have the screw
turned in almost all the way. I have been told Lycoming makes three different springs, with different wire sizes. I am looking into buying a heavier
spring to boost my pressure up to 80PSI.
 
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oil pressure

There is a lot of info on the benefits of high oil pressure, you just have to search for it. Since Cessna resumed single production they have been taking the oil pressure for the gage from the front of the right hand oil gallery. This results in about ten pounds more "real" oil pressure IF the oil pressure is adjusted to the previous reading from the accessory case location.
The consensus is that this is an attempt to provide better valve stem lubrication. There is quite a bit of expert support for this, other very experienced engine people say that anything in the green arc is fine.
 
oil pressure

Google "oil pressure Cessna 172" and look for the article by Bill Marvel and Bill Scott.
 
Google "oil pressure Cessna 172" and look for the article by Bill Marvel and Bill Scott.

I found the article. Interesting info. I wonder how my 0235 C-1 with mechanical lifters fits into the equation. I definitely want to get my pressure
up to the max limit of 80-85. I was just told that I could put up to three
washers under the spring on my adjustable relief valve which I always
thought the washers were only for the non-adjustable type valves that
had to use washers as the only way to adjust. Could someone please verify
this.

Thanks
Jim Miller
 
oil pressure

There are also different springs for the 0 320/0 360.Don't know if they are the same for the 235.
 
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