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Oil Pressure Oddity

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JohnF

Joined: 13 May 2010
Posts: 124

Posted: Sun Jul 16, 2017 10:02 am Post subject: Oil Pressure Oddity

Van's RV-12 Rotax 912-ULS



After new oil line install I now have a strange (to me) oil pressure indication



When I start the engine and taxi out the oil pressure reads typically 58-psi at 150-degrees F.  When in cruise at 5100-rpm the oil pressure reads around 41-psi at 200-degrees F. That's at the bottom of the green arc. Reduced power in the pattern at 3300-rpm oil reads 58/205 or so.



Standing still after taxi in, oil temp/pressure stays around 58/195 (at)4000rpm



This all seems backwards to me. The oil level is full..right up to the flat on the dip stick. Not using any oil, engine runs fine...



Your ideas?

DHeal

Joined: 15 Feb 2017
Posts: 3

Posted: Sun Jul 16, 2017 10:20 am Post subject: Re: Oil Pressure Oddity

What "oil line" did you change?  Is oil line installation still per Van's plans?  Did you do an oil system "purge" after you changed the oil line?  Need more info.

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Sun Jul 16, 2017 11:49 am Post subject: Oil Pressure Oddity

Yes, oil system purged twice...all lines were replaced using Aircraft 

Specialty 'drop-in' made to spec lines.



John

---

davidjoyce(at)doctors.org
Guest

Posted: Sun Jul 16, 2017 1:22 pm Post subject: Oil Pressure Oddity

On 2017-07-16 20:49, John Fasching wrote: [quote] [quote]--> RotaxEngines-List message posted by: "John Fasching" <n29cx(at)ridgeviewtel.us (n29cx(at)ridgeviewtel.us)>  Yes, oil system purged twice...all lines were replaced using Aircraft Specialty 'drop-in' made to spec lines.  John ---

b.carl@sympatico.ca

Joined: 20 May 2008
Posts: 77

Posted: Tue Jul 18, 2017 7:14 am Post subject: Oil Pressure Oddity

Hi John

Have you found the problem?

Carl



---

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Tue Jul 18, 2017 7:47 am Post subject: Re: Oil Pressure Oddity

No, Carl, I have not resolved the oddity yet...no time to work on it..perhaps in a few days...will post any results.

John

b.carl@sympatico.ca

Joined: 20 May 2008
Posts: 77

Posted: Wed Jul 19, 2017 4:03 am Post subject: Oil Pressure Oddity

Hi John

Had the exact same problem when my engine had 142 hrs; it now has 850.

After a lot of experimenting I traced the problem to the relief valve. Rotax 

wanted to sell me a new pump.

The fix was to make shims out of ,016 and .025 aluminium to place under the 

check valve spring  to find the right combination to solve the problem.

Cheap and it worked..

Good luck

Carl



---

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Wed Jul 19, 2017 7:43 am Post subject: Re: Oil Pressure Oddity

Thanks, Carl, now I have to figure out where the check valve is...have printed rotax manuals so I should be able to find it...so many other life-related things going on right now so its going to be a bit before I can plunge into this.



I thank you very much for your assistance.



John

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Wed Jul 19, 2017 8:56 am Post subject: Re: Oil Pressure Oddity

Thanks again, Karl. I found a rotax service bulletin with drawings and instructions for the shim and its location, etc. All pretty straight forward. Now to find the time to open the cowling and have at it. Thanks again.

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Thu Jul 20, 2017 5:04 am Post subject: Re: Oil Pressure Oddity

Do not shim the oil pressure unless you double check the oil pressure with a separate mechanical gauge. It's very rare a Rotax has a real oil pressure issue at the sprint and ball bearing. Many people over pressure a system by doing this without double checking. 

It is quite normal for the oil pressure to drop or fluctuate some as the engine warms and with more rpm.

Air in the oil pressure hose can cause this and will work its way out.

More likely causes are a poor ground. A poor ground will cause the oil pressure to drop as throttle is increased and it goes back up when throttle is reduced. To rule this completely out take a wire and go around the ground that is in place and or tighten all grounds tight. A meter usually will only show that you have a ground, but not that it is solid or poor.

The second most common is the sender going bad. Depending on what sender you have they work on resistance and it just needs to be replaced.

VDO's did this and the Honeywell senders had issues to.



p.s.

41 psi is still acceptable even if the sender is off.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

b.carl@sympatico.ca

Joined: 20 May 2008
Posts: 77

Posted: Sun Jul 23, 2017 9:48 am Post subject: Oil Pressure Oddity

Hi John,

Good idea to read the tech manual, I did all of those thing that Mr Lee 

recommends and more; found nothing cured the problem. The Rotax people in 

Vernon said they knew of three other engines with the same problem and 

changing the pump was the cure. After two weeks of changing parts: oil lines 

,oil, oil filter, check valve and measuring oil intake suction and outlet 

pressures I finally exchanged the complete oil pump from a friend's engine 

and found my engine worked just fine with his pump. That proved to me that 

the problem was in the pump.

The Pump is a simple gear type; it either produces pressure or it does not 

Mine produced good pressure for 10 minutes then in less than a minute 

dropped by ~10 psi. I knew then it had to be the check valve.

My fix was 14 years ago and it was a combination of one or two .016/025 alum 

shims, (I do not remember exactly). that solved the problem  It  has worked 

like a charm.for a further 700 hrs  My press after a total of 856 hrs is a 

solid high 60 low 70 on start and settles to 50/52 after warm-up

I just remembered that  my oil press gauge needle fluctuated slightly before 

the fix; now it is steady This maybe a further symptom of this problem..I 

recommend you try this fix before you start disassembling the rest of your 

oil system.

---

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Sun Jul 23, 2017 3:32 pm Post subject: Re: Oil Pressure Oddity

Thank you,  Carl,



I have a bi-annual flight review scheduled for tomorrow and then after that I will, over the next few days, pull the cowl and try the shims you suggest. I had already de-oxed and re-tightened connections to the oil pressure sender and nothing there helped...will let you and the other readers on this site, how the shim change worked out.



Thanks again.

John

AmphibFlyer

Joined: 29 Dec 2009
Posts: 25

Posted: Mon Jul 24, 2017 4:19 am Post subject: Re: Oil Pressure Oddity

 	  JohnF wrote: 	
		  ... I will... pull the cowl and try the shims you suggest. 	




Before you do anything else, I suggest replacing the oil pump's pressure spring, part no. 838122. It tends to wear along the side, and that affects the oil pressure.

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Mon Jul 24, 2017 9:46 am Post subject: Re: Oil Pressure Oddity

OK, I just ordered a replacement new spring, due in a few days, and will dig into this when its received.



FBR went just fine today...good for another two years. 



thanks again, men.

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Sun Jul 30, 2017 8:57 am Post subject: Re: Oil Pressure Oddity

I received the new oil pressure relief spring and installed it yesterday. The actual installation only took two minutes, but I spent a miserable 1.5-hours putting back the lower cowl. Since installing the new oil hoses the oil cooler doesn't "hang" as before and getting the bottom of the cooler notches to slip into the cowl's engagement 'knobs" is a real pain. I finally wedged a small soft foam ball between the oil cooler and the muffler to properly position the cooler so that it would engage the 'knobs'....but what a pain. Was able to reach in from behind to remove the ball after the cowl was on.



I flew this morning....idle and taxi pressures 55-60-psi...in flight at 5030 rpm the oil pressure ran 45-psi, about 4-psi more than before....stayed there during the flight....upon landing and taxi it rose again into to 50-or-so range.



I am going to live with this for a while before trying anything else...as Roger said, it might be an air bubble that might work it self out..



More if progress is made.

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Mon Jul 31, 2017 7:40 am Post subject: Re: Oil Pressure Oddity

Hi John,

The results you are now getting can be fairly normal as the idle and cruise oil pressure can be a little different. Many times this ends up the sender causing the problem and can even be a digital instrument software issue.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

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