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Question about oil pressure and when it bypasses

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2 weeks 4 days ago #22002 by amhst56@gmail.com
Question about oil pressure and when it bypasses was created by amhst56@gmail.com
Hi all,

Now that my leak is fixed and I'm flying, I noticed the oil pressure dropping from 35 at 2000 rpms to 25 at 3000 rpms when I was waiting for it to warm up yesterday.

As the rpms are raised the pressure goes down, I'm assuming this is from the bypass?

On take off, pressure was going down to 25 psi and for a short field takeoff, climbing at Vx and 950ft per minute, pressure dropped to 20 psi. When I leveled off it was in the green again

The guage on my plane is yellow from 30 psi to 12, then red. Because it was in the yellow, I was concerned.
I checked the operators manual and min is 12 and I believe max was 70.
Is hitting 20 psi normal for takeoff?

I have the old bypass bolt, should this be replaced to the new style with the cone instead of the ball?

I also have some fluctuations every 5 or 10 seconds during warm up, nothing like the video on here. So I tightened all the ground screws. Are these fluctuations normal also?

Sorry for so many questions, since it's new to me I don't what her normal is yet.

Any input would be appreciated!
Thank you

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2 weeks 3 days ago #22007 by Bill Hertzel
Replied by Bill Hertzel on topic Question about oil pressure and when it bypasses
The Oil Pressure Regulator typically opens to limit the Oil Pressure to the 40-50psi range.
The pressure should change slowly with temperature or throttle but generally will be as steady as a rock.

At a Warm/Hot idle, the pressure will drop because the engine is using all the Oil the Pump is delivering.
The 12-30 Yellow band is OK below 3500 rpm.
Above 3500 rpm you should ALWAYS be in the GREEN. (30-70psi) (Typically 40-60)
20psi or anything below 30psi at full Takeoff Power is an ABORT indication.

You may have a restriction in the Oil Pump Input line. (Oil Tank >>> Oil Cooler >>> Oil Pump.)
Look for Kinged, Crimped, Collapsed Hoses.
Any leak will draw in Air, not spray oil.
These hoses are under Suction, Not Pressure.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
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2 weeks 3 days ago - 2 weeks 3 days ago #22010 by Roger Lee
Replied by Roger Lee on topic Question about oil pressure and when it bypasses
You may also just have a poor ground. This is a symptom of a poor ground. I have fixed many by just tightening the grounds.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last edit: 2 weeks 3 days ago by Roger Lee.

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2 weeks 3 days ago #22012 by amhst56@gmail.com
Replied by amhst56@gmail.com on topic Question about oil pressure and when it bypasses
Thx Bill,

I will double check the input side.
Everything I remember was really gradual bends.

The oil tank is on the pilots side firewall --> thermostat on passenger side --> oil cooler on passenger side firewall (inlet/outlet sideways, not up) --> oil pump.

Seems like it's a longer run than normal.
Aren't most oil coolers in front of engine?
If so, could it be the long run?

If I can't find any leaks or kinks, next step would be to remove the oil sender and put an oil pressure guage on it to determine if the electric oil pressure guage readings are accurate and go from there?

Thx

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2 weeks 3 days ago #22013 by amhst56@gmail.com
Replied by amhst56@gmail.com on topic Question about oil pressure and when it bypasses
Thx Roger,

When researching if this was normal, I did come across one of your posts that state a ground might be the cause. So I tightened all the grounds on the bus.

Any other place? Or can I add one temporarily to see if it helps?

If I remember correctly, 2 purple, white, and red were in the back. The white went to pump, would the red or purple be ground?
Or is the mount grounded?

Thx

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2 weeks 3 days ago #22020 by Bill Hertzel
Replied by Bill Hertzel on topic Question about oil pressure and when it bypasses
Standard UMA Gauge colors...
2x Violet = Internal Gauge Lighting.
White = Signal from Pressure Sender
Red= 12v Power
Black = Ground

Remember that the Engine mount is Rubber cushioned and does Not naturally Ground the Engine Block to the Airframe.
The Ground cable for the starter to the battery usually serves the function of grounding the block to the Airframe.

Temporarily installing a Fully Mechanical Pressure Gauge is worth the effort to verify that the problem is real or the indication is false.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
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2 weeks 3 days ago #22023 by amhst56@gmail.com
Replied by amhst56@gmail.com on topic Question about oil pressure and when it bypasses
Hi Bill,

I took a 30 sec video of what I was seeing.

After you mentioned that there could be a kink in one of the hoses and I looked at them, I thought for sure that was the issue.
(Took video of it also)

I did throw the mechanical oil pressure guage on just to be certain and sure enough, that one was reading steady 35 psi at around 4000 rpms.
(Took video of that also)

With mechanical guage on, I ran it up to 5800 and it was a steady 40 psi. (Didn't video that)

photos.app.goo.gl/57sNJEnfjzyc4K7o9

I had the guage out the other day and don't remember a black wire. Will double check.

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2 weeks 3 days ago - 2 weeks 3 days ago #22024 by Bill Hertzel
Replied by Bill Hertzel on topic Question about oil pressure and when it bypasses
If I interpret the Videos correctly, it looks like that as you increase RPM, the Mechanical Oil Pressure indicates above 40 PSI and the electrical Oil Pressure drops below 30.
I would track down the Black ground wire at the gauge.

Installation Manual.
www.aircraftspruce.com/catalog/pdf/10-02417install.pdf

If it makes absolutely no sense and appears that Magic is at play, It is a Grounding problem!


Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
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Last edit: 2 weeks 3 days ago by Bill Hertzel.

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2 weeks 3 days ago #22025 by amhst56@gmail.com
Replied by amhst56@gmail.com on topic Question about oil pressure and when it bypasses
Thanks for the link.

I did track down the black wire.
Looks like all the black wires for all the gauges are soldiered together and electrical taped. Then one wire goes to the ground bus under dash and the other goes through the firewall.

Nothing is broke.
I will clean the connection at the bus and add an additional ground that jumpers out the soldiered connection.
Anything else I should try?

If it is the ground, wouldn't all other gauges be messing up also?

Thx again for all your help!

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2 weeks 3 days ago #22026 by Bill Hertzel
Replied by Bill Hertzel on topic Question about oil pressure and when it bypasses
Is the sender a 1 wire or a 3 wire device.
If a 1 wire device, the return is through the block and the ground may be floating.
As the RPMs come up, the ground voltage rises above Zero, making the sender appear to be going down.

And , No it doesn't make any sense to me either. :unsure:

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
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2 weeks 3 days ago #22028 by Roger Lee
Replied by Roger Lee on topic Question about oil pressure and when it bypasses
No. If it is a 2 pole sender it needs it's own ground. If it is a 1 pole sender it gets its ground from the engine and that's one reason if you have a single pole sender to not apply Teflon tape. If you have two sender just attach an alligator clip to the ground on the sender and then to a known good ground and start the engine. If it is a single pole sender attach the clip right to the sender body's edge.
If this fixes the problem find the bad ground.

Plus like Bill suggest you can always double check the system with a mechanical gauge just plumbed in. You can buy all the few parts you need for this ate Ace Aviation (Ace Hardware). You don't need anything fancy you're just going to take a quick look to see if everything is saying the same thing. Use tiny 1/8" tubing. At the end where the gauge is just leave it a tad loose and start the engine. The pressure will purge the air out of the tube and when you see a drop or two of oil come out around the gauge threads snug it up. Now all the air is out. Piece of cake.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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2 weeks 3 days ago #22029 by amhst56@gmail.com
Replied by amhst56@gmail.com on topic Question about oil pressure and when it bypasses
It is 1 wire yellow wire from sender.
(I think the pic cut off the wire though)

How do I know if block is floating?

The negative battery wire goes to a bolt on the frame then splits 2 ways, one going towards the engine for the starter I assume. Which would ground the rest of the engine right?

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2 weeks 2 days ago #22033 by Bill Hertzel
Replied by Bill Hertzel on topic Question about oil pressure and when it bypasses

amhst56@gmail.com wrote: ...How do I know if the block is floating?...


Use a quality Ohm meter.
If it has OHM and DIODE selections, do NOT use the Diode function.
They are Not the same.

Select OHMS and touch the two meter leads together.
Most meters will not read 0.0. you might see 0.2 or something close.
Remember this reference number.

Now, Ohm from the Body of the Sender Can to the ground point as close to the panel gauge as you can get.
The case of the gauge may be ground but the Black wire is what you want.
You should see the same number or very close. (ex. 0.3)
If you see something bigger than 1.0 plus your reference number (ex. 1.3), further investigation is needed.
- - - - -
You are trying to measuring very small resistance values and hand meters are Not the best tool for doing this, but it is all you likely have without spending a few hundred dollars for a 4-probe Milliohm-Meter that will have limited use.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
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2 weeks 2 days ago #22037 by Roger Lee
Replied by Roger Lee on topic Question about oil pressure and when it bypasses
The blue wire in your picture is from the temp sender. Look on the other side in your picture. That VDO sender screwed into the side of the oil pump is the oil pressure sender. Does it have a single wire or two? Sounds like a standard battery / engine ground.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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2 weeks 2 days ago #22042 by amhst56@gmail.com
Replied by amhst56@gmail.com on topic Question about oil pressure and when it bypasses
Bill,
great instuctions!
I will try that, thank you for that.

Roger,
Single yellow wire that is spliced into the white wire of the oil pressure gauge.

You seem to be and I'm hoping you are right about the ground wire.
Did you watch the video?
Thanks for the help

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2 weeks 2 days ago #22045 by Roger Lee
Replied by Roger Lee on topic Question about oil pressure and when it bypasses
The ground wire causes your symptoms and just needs to be ruled in or out as a cause. It is a quick, cheap and easy check and I have seen it be the cause many times. This of course doesn't rule out other things just this one.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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2 weeks 2 days ago #22048 by amhst56@gmail.com
Replied by amhst56@gmail.com on topic Question about oil pressure and when it bypasses
.7 ohms through the meter and alligator clips.

Stripped wire on guage side of solder joint then to sender ( just in case something was bad with that splice and got .7 ohms.

Guessing the ground is good and next would be to test sender?

Thx

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2 weeks 1 day ago #22053 by amhst56@gmail.com
Replied by amhst56@gmail.com on topic Question about oil pressure and when it bypasses
Not sure how to check sender, but was thinking to remote mount the sender and trying that.

The pic below is from kitfox relocation kit.
Can I use braided fuel line since I'm experimental?
I was assuming I would need a fire sleeve, but kitfox's kit doesn't have one.

Thoughts
Thx

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2 weeks 1 day ago #22054 by garrett
I remote mounted my sender years ago with stainless steel teflon line with fire sleeve. Have not had a problem with the sender since. The vibration and heat will damage the sending unit.

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2 weeks 1 day ago #22055 by amhst56@gmail.com
Replied by amhst56@gmail.com on topic Question about oil pressure and when it bypasses
Auto parts braided line?
I'm thinking it would be fine since my main oil inlet to the pump is held together by a nipple and a hose clamp

Where did u get the fire sleeve?
Thx

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