Flickering Oil pressure

[Ben Longden]

During an inflight check of the panel yesterday, I noticed the oil pressure gauge needle flicking wildly.

 

With power applied, the needle was buzzing in the green, but I decided to abandon the flight and head for home.

 

Turning base with power back, the flickering became fairly wild, with it falling into the red, and going up into the yellow.

 

Engine temp was normal, sound was normal and behaviour was normal as was the smell. The engine oil was checked twice (once by me before fuelling and again by an instructor after refuelling) and was... well... normal.

 

Another check of the dipstick after parking, showed the level was.. still prefectly normal.

 

Any ideas?

 

Ben

 

 

[slartibartfast]

Almost certainly electrical Ben. The gauge was flickering, not the pressure.

 

Loose wire somewhere I would wager if I were a betting man.

 

I did buy a lottery ticket in 1976 but I didn't win, so I gave it away.

 

 

[BigPete]

Has the aircraft just had a service - as in oil and filter change?

 

regards

 

 

[Guest pelorus32]

Which a/c Ben?

 

Mike

 

 

[Guest Cloudsuck]

Hi Ben,

 

You are not alone. There are three aircraft on my field with the same problem including mine. The fix is simple.

 

Before my 1st service, my pressure used to run smooth at 3.5 bar with the run-in oil. After changing at 25hrs, I got the wild flickering.

 

I had been told about it by the owner of two other new aircraft on the field who was having the same problem. Trying to fix the problem, they had changed the sender, relief valve spring and in the end the oil pump but still couldn't fix it. The flickering was still there with a mechanical gauge so it wasn't electrical.

 

After my 1st service and using better oil, my pressure would run smooth at 4 bar at 1800 rpm (idle). As soon as you opened the throttle, the pressure would start flickering wildly and drop down around the 2.5 bar mark (just in the green). I have a trade background in hydraulics and to me this appeared that the relief valve was popping off above 4 bar and chattering causing the pressure to drop at higher rpm in a flickering manner. The problem only came about as a result of changing to a better oil which caused higher pressure and popping off the valve. The higher the rpm the worse the oil pressure and flickering got.

 

I called Wally and he said that this was not a common problem and the only 912's he had heard of doing this were on my airfield. He told me to try changing the oil from GPS to Shell. He was very dismissive. In the end I placed two shims (total 1.8mm) under the relief spring and now I have a solid 4.75 bar, non flickering. I rang Rotax and told them of my findings but they were not really convinced. In six months there will be an advisory out for sure.

 

Regards,

 

 

[Ben Longden]

Which a/c Ben?Mike

5159, Mike.

 

The funny thing was the problem was not there at startup.. Just saw it start to happen when in cruise. Needle fine, then she started to flicker.

 

Gut feeling is a dodgy sensor and or connection.

 

Ben

 

 

[Guest pelorus32]

G'day Ben,

 

the problem was there to a certain extent last Sunday when I flew 5159. I queried it and was told that it is a sensor problem. The a/c had just had an oil and filter change a few days before.

 

What I saw was towards bottom of the green oil pressure and it fell a bit under load - quite disconcerting.

 

Regards

 

Mike

 

 

[Guest dracer]

earth wire?

 

 

[Guest Cloudsuck]

If it is going into the red, please don't fly it until they put a mechanical gauge on it and check it. They will soon see that it is not electrical.

 

 

[Yenn]

Jabiru have had a problem like this for a while and they advised me when I bought the new 2200 engine that if I had flickering pressure it was possibly caused by a loose piece of sealant getting into the pressure relief valve. The fix was to remove the valve and spring and thoroughly clean the area. It hasn't happened to me but that may be your problem. Talk to the engine section at Jabiru they may have more info now.

 

When I posted this I thought it was in the Jabiru location, my eyes must have gone slanted. But it still may apply.

 

 

[Ben Longden]

If it is going into the red, please don't fly it until they put a mechanical gauge on it and check it. They will soon see that it is not electrical.

Thats why I aborted the flight as soon as it happened... I would prefer to practice my forced landings in my OWN time... ;)

 

Nice to know the issue is under control, and that its a dodgy sender.

 

Ben

 

 

[timshel]

This happened to me last week. I have a p92 echo super rego 5391 so quite new. LAME had a look and it Turned out it was the earth/sender wire on the top of the sender unit. The thumb screw was a bit loose and at higher revs it was breaking contact. :sad:and it is not a lockable nut. I expect therefore it will happen again.

 

 

[Bruce]

Further to Tim's comments, the small white wire that commects to the sender can flex up and down in the airflow through the cowl. I had one Echo Super where the flexing caused the wire strands to progressively break. As this happened the gauge fluctuated, eventually going straight off the top of the guage when it broke right through. Happened on a NSW Sierra as well. Crimp a new connector and cable tie the wire to reduce flexing movement.

 

Also had a faulty sender on another aircraft

 

Regards

 

Bruce

 

 

[Guest Maj Millard]

Hey nothing wrong with the senders, just put a dab of silicon (clear or hightemp) on the little push on connectors at the engine. Have been doing it for years and guess what ? ...never get flickering guages.