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05-23-2018, 10:07 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by tim2542
You are really at a fork in the road here and you cannot know which to take until you determine if it’s a gauge or engine problem. Buy beg or borrow a mechanical gauge and see what the actual pressure is. Then you will know if you have an engine problem or a gauge problem. Any other course is guessing.
Tim Andres
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If he has had 70 PSI in cruise for four years and still has 70 PSI in cruise, why would you assume the gauge is now incorrect. wondering if I missed something here.
Larry
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N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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05-24-2018, 05:27 AM
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Super Moderator
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,627
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First course of action
It may not be the gauge, or the sender, but it is always the first course of action to verify the gauge. Otherwise, you may damage the engine by adjusting something out of range with an erroneous indication. That's all.
Vic
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 Vic Syracuse
Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
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Author "Pre-Buy Guide for Amateur-Built Aircraft"
www.Baselegaviation.com
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05-24-2018, 08:10 AM
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Join Date: Mar 2005
Location: DVT Phoenix
Posts: 1,187
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While it might not be the GA or sending unit. I believe it would be prudent to verify such before tearing stuff apart. FWIW, being a retired mechanic for 50+ years that would be concidered proper procedure in any shop I worked at. Easy to get a mechanical GA and proper hose with a 1/8th pipe adapter at a parts store, remove the sender install the GA and compare setting while running on the ground. They will either be the same or maybe not. Give us a follow up and good luck.
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Larry
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05-24-2018, 12:54 PM
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Join Date: Jan 2005
Posts: 3,646
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Quote:
Originally Posted by Larco
While it might not be the GA or sending unit. I believe it would be prudent to verify such before tearing stuff apart. FWIW, being a retired mechanic for 50+ years that would be concidered proper procedure in any shop I worked at. Easy to get a mechanical GA and proper hose with a 1/8th pipe adapter at a parts store, remove the sender install the GA and compare setting while running on the ground. They will either be the same or maybe not. Give us a follow up and good luck.
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Out of curiousity, can one be reasonably certain that a gauge accurately measuring oil pressure at idle would also accurately read oil pressure at a higher power setting, or do you have to compare gauges at a variety of power settings to be sure they are acccurate?
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Steve M.
Ellensburg WA
RV-9 Flying, 0-320, Catto
Donation reminder: Jan. 2021
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05-24-2018, 12:57 PM
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Join Date: Feb 2011
Location: Suwanee, GA
Posts: 415
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Thanks for all the suggestions. The 100psi when cold is when the weather is cold, and as the oil warms up the pressure did go down to 70 at idle or with power up.
Now as soon as I get it started it is in the 25-30psi, but increases to 70 as power is increased.
This change did happen from 1 flight to the next, it did not degrade slowly.
I will check with a mechanical gauge, but don't have any hopes that it is really the problem.
Hope to look into it this weekend.
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05-24-2018, 01:35 PM
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Join Date: Dec 2013
Location: SLC, UT (KBTF)
Posts: 240
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Was there an oil change involved?
If so, did you change brands or viscosity?
Cheers, David
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05-24-2018, 04:47 PM
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Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,393
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Oil Pressure
The new limits which have been in effect for several years are 115 red line and 95 top of the green arc. I like to see high 80's in cruise, especially if any aerobatics are being done.
While verifying pressure with a mechanical gage is standard protocol, the steady 70# in cruise would indicate the gage and/or sender are not the issue.
I suspect you have a small piece of debris in the pressure relief valve. Depending n baffling this is pretty easy to check. Just behind the #3 cylinder is the pressure relief valve screwed into the case. Two different types. If you have a castle nut on the end of a threaded shaft turning the nut clockwise increased the pressure. If no nut the valve must be removed. Use a new crush gasket when reinstalling. You will probably need to remove some baffling to remove the valve
If the valve is the non adjustable type I would recommend installing three additional washers to raise the cruise pressure.
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05-24-2018, 10:42 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by alpinelakespilot2000
Out of curiousity, can one be reasonably certain that a gauge accurately measuring oil pressure at idle would also accurately read oil pressure at a higher power setting, or do you have to compare gauges at a variety of power settings to be sure they are acccurate?
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The sensor simply has a diaphragm and a spring (assuming traditional sensors - transducers, like the Kavlico are a different animal). A lever tied to a rheostat is connected to the diaphragm to measure it's movement. It would be rare to have one of these types of sensors be accurate at one PSI and significantly inaccurate at another. Tests are usually conducted in the middle of the range or at the pressure typically read, though sweeping the gauge is good practice and doesn't take much time.
Larry
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N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 05-24-2018 at 10:49 PM.
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05-24-2018, 10:56 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by bill@fusion4.net
Thanks for all the suggestions. The 100psi when cold is when the weather is cold, and as the oil warms up the pressure did go down to 70 at idle or with power up.
Now as soon as I get it started it is in the 25-30psi, but increases to 70 as power is increased.
This change did happen from 1 flight to the next, it did not degrade slowly.
I will check with a mechanical gauge, but don't have any hopes that it is really the problem.
Hope to look into it this weekend.
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As I mentioned, pre-pump blockage can cause these symptoms as well. If you haven't done so in while, it would be wise to also check the screen in the sump. If you have a lot of blow by, you would be surprised how fast the little carbon checks seemingly reproduce. These can clog the screen up.
Larry
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N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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05-24-2018, 11:59 PM
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Join Date: May 2010
Location: Benaraby Queensland. Australia
Posts: 209
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From what has been said before it appears that you have low pressure at low revs, but good pressure at normal revs. It happened suddenly, not over time.
So what could be the problem.
Bearings loose and letting pressure escape. Possible but in my opinion unlikely.
Pump worn and not able to provide enough flow, again unlikely to have happened so suddenly.
That leaves pressure escaping at low flow rates, but as flow increases pressure builds. So where could pressure escape? Most probable cause is something stuck under the pressure relief valve. Pull it, clean it and then see what happens.
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