Rotax 912 oil pressure fluctuations

[raizo]

Thanks for your comments everyone, Geoff, the PRV is located at the bottom of the oil pump and the mushroom is a replacement part for the normal ball and spring component of the PRV its suppose to eliminate the flutter problem but as I have discovered on the Rotax Owner forum it often does not get rid of the problem, as you pointed out it may not be seated properly ,as stated we changed all the oil lines so there is no obstruction there, will check the breather lines though will also check all fitting on the oil tank(may as well check everything) and yes we purged the system after replacing the oil lines.Our next step is to remove the pump and have it checked and maybe change back to the ball and spring????? As yet no reply from Bert Flood

 

 

[raizo]

HI all, a quick up date, I had also posted this thread on the Rotax owners forum, and just had a reply from a USA based Rotax mechanic who was dealing with the exact same problem on the same aircraft RV12 they tried exactly what I had done with the same results they then tried a borrowed oil pump housing and the problem went away so on further inspection of the old housing sever chaffing of the PRV seat was found, they then inspected 5 other housings and not one was chaffed, A fellow club member who has been helping me has offered his oil pump housing to try to see if this may be the problem, if so Mr Flood will be getting a phone call

 

 

[geoffreywh]

Yes I know about "purge" I think its a poor choice of words...Probably translated from the German "säuberung" which means, in my German anyway, "cleaning" Cheers G

 

Anyway The remove oil pump and PRV and look at closely is a good plan.

 

 

[skippydiesel]

Good old Uncle Sam coming to the rescue - hope they/you have finally got to the crux of the matter.

 

 

[raizo]

Have removed the oil pump housing and sent it of to Bert Flood for inspection,will keep you posted

 

 

[raizo]

Latest news.,Bert Flood inspected the oil pump housing and found a discrepancy in the seat of the pressure relief valve as compared to a new one so they sent me a new one to try and glad to report a 90-95% improvement.instead of large fluctuations of between 20 and 60 psi i now have a small vibration type fluctuation of 2-4 psi which could be caused by an air bubble somewhere.

 

 

[geoffreywh]

I knew it!, Well I didn't know , but I suspected...

 

" When you have eliminated the impossible, whatever remains, however improbable, must be the truth."

 

― Arthur Conan Doyle, Sherlock Holmes

 

Congratulations

 

 

[IBob]

Latest news.,Bert Flood inspected the oil pump housing and found a discrepancy in the seat of the pressure relief valve as compared to a new one so they sent me a new one to try and glad to report a 90-95% improvement.instead of large fluctuations of between 20 and 60 psi i now have a small vibration type fluctuation of 2-4 psi which could be caused by an air bubble somewhere.

Excellent outcome, finally! And thank you for posting this: no doubt others will benefit.

 

 

[skippydiesel]

Latest news.,Bert Flood inspected the oil pump housing and found a discrepancy in the seat of the pressure relief valve as compared to a new one so they sent me a new one to try and glad to report a 90-95% improvement.instead of large fluctuations of between 20 and 60 psi i now have a small vibration type fluctuation of 2-4 psi which could be caused by an air bubble somewhere.

That's great news, however you should not have a "small vibration type fluctuation of 2-4 psi" - damping by the sender/gauge should take care of any tendency for this sort of low level oscillation.

 

 

[skippydiesel]

Vdo part number 360-003Plenty on eBay also

Jason

Hi Jason,

On the strength of your advice I went out and purchased the above VDO sender. It turns out to be:

 

700KPA, 100psi, 10-73 ohms, 1/4 18 NPT, Blade/screw 4mms terminal-

 

Decided to install it at next "heavy maintenance service" ( 800 hrs & 5 year rubber replacement) This has taken quite a while to come around hence the delay in writing.

 

You guessed it ! - VDO PN 360-003 doesn't fit my 912 ULS. (NOW FOR SALE - anyone interested??)

 

My existing pressure sender has what appears to be parallel male 9.67mm wide/thick x 9mm long (measured using callipers) threaded connection. This" drives" a Speco 0-100 psi gauge that is rated at 33 ohms (unable to get more detailed specifications)

 

It appears I may need one of the two following senders:

 

VDO PN 360-022

 

500 KPA, 75 psi, 10-183 ohms, M10 x 1.0, Blade/screw 4mms terminal

 

(This is about $60.00)

 

OR

 

VDO PN360081032002C

 

0-5 BAR, (75 psi), 10-180 ohms, M10 x .0, Blade/screw 4mms terminal

 

(About $150.00)

 

I have been unable to contact VDO or Howard Instruments both located in Vic (on holiday??) for advice.

 

All informed comments most welcome.

 

 

[skippydiesel]

Finally got on to VDO technical advisor.

 

Seems, VDO PN 360-022 & VDO PN360081032002C do in fact have almost identical operating performance/specifications. The exception would seem to be the number of terminal and functions.

 

• VDO PN 360-022 - has one terminal and is made in India
   
   
  
• VDO PN360081032002C - has two terminals. The second is a light switch connection for a warning light and is made in Germany.
   
   
  

 

 

The manufacturing location explains, at least in part, the radically different purchase price.

 

The other little gem of information offered, is that if the sender has a resistance of between 0-12 ohms the system will run between 0-180 ohms. I dont [pretend to understand all this but my existing/old sender has a resistance of 3.6 ohms.

 

 

[skippydiesel]

Seems I misread the Speco gauge specifications. It should be :

 

00 psi 240 ohms

 

50 psi 103 ohms

 

100 psi 33 ohms

 

VDO advise that their 10mm senders will make the Speco gauge read in reverse.

 

Advice comments urgently required.

 

 

[ianboag]

Seems I misread the Speco gauge specifications. It should be :00 psi 240 ohms

 

50 psi 103 ohms

 

100 psi 33 ohms

 

VDO advise that their 10mm senders will make the Speco gauge read in reverse.

 

Advice comments urgently required.

You can buy Chinese VDO compatible senders for ridiculously small amounts like $25 or so. We have several in use on our field ....

 

 

[skippydiesel]

You can buy Chinese VDO compatible senders for ridiculously small amounts like $25 or so. We have several in use on our field ....

Hi ianboag,

 

How about the contact details ????

 

 

[ianboag]

Hi ianboag,How about the contact details ????

Autogauge Oil Pressure Sender Unit - Yellow Label

that's the NZ equivalent of EBay ... it's the unit I run on my 912ULS. If you go to EBay Aus and look for oil pressure senders you will find ... as I recall it is a 10 bar unit which I mention to my MGL unit. It is written on the body .....

 

Universal Engine Oil Pressure Sensor Gauge Sender Switch Sending Unit 1/8 NPT | eBay

 

Looks to be the same thing for $7.50 with free shipping from China. At that price one doesn't care if they are AUD, NZD or USD .....

 

I suspected that the wild oil pressure fluctuations I saw in another aircraft were an artifact of the Dynon EFIS, so plumbed in on of these ,,,, pressure was rock steady. Nylon hose with fittings was another $20

 

TRISCO OIL PRESSURE GAUGE 52MM

 

 

[raizo]

Well it,s been nearly a year since i last posted ,March last year,and sadly my pressure problem returned as bad as ever and not long after fitting the new oil housing about 5 hours of flying,For those of you not familiar with my problem my oil pressure fluctuated horribly between 30 and 80 psi so bad the needle on the manual gauge was a red blur, and the MGL gauge was unreadable, GOOD news is i posted this problem on the Rotax forum along with a fellow RV12 owner in the US with similar problems and a gentleman(a retired engineer ) in the US came up with the answer, he studied the problem for some time and lots of phone calls and emails later he had the solution,the problem arises when the mushroom valve is pushed back from its seated position and then in my case(and others) the head of the valve starts to bobble around(like one of those toy dogs with the wobble head) this is evident by the marks on the valve stem, The 912 IS has a different oil valve ,its a piston style so can only travel up and down and does not bobble about (it is also larger than the 912ul valve),so he manufactured a valve using the piston idea to suit the 912ul motor,myself and a gentleman in the US have been testing this valve as well as talking to the Rotax engineering department for the past 9 months and are VERY pleased to say ,i myself have over 70 hours of flight time with rock solid oil pressure and Alex in the US has 40 plus hours,so anyone with oil pressure problems ,we have the answer. If anyone is interested i can put you in contact with Bill in the US who came up with the solution

 

ps this is still in testing phase but some more testers would be good,Rotax have shown great interest in the valve and are eagerly waiting for our results

 

You can follow my,and Alex path on the Rotax owner forum ,search Sever jittering oil pressure and on page 5 is a link to the answer.