Oil pressure issues on 0-200

[Gordon Low]

Hi all

I am based in New Zealand and own a well maintained Citabria 7ECA – 318 which is powered by a Rolls Royce Continental 0 200.

The engine has run approximately 500 hours since last overhaul and uses very little oil between 25 hour oil changes. Currently running W100 oil. It normally runs flawlessly.

I have two issues that I hope that someone 'in the know' may be able to give me advice on. Firstly, very occasionally – perhaps once every 20 hours and interestingly near oil change time (Especially on cold morning after the aircraft hasn’t been flown for a while) – The oil pressure does not rise on the gauge. After advice from my engineer who understood there would be pressure in the engine, he suggested to carry on warming up then, when the revs are increased to around 1500rpm, the pressure would rise to normal which it did.

Secondly, around 2 years ago, my engineer was away on a trip when the oil pressure dropped to the bottom of the green range (30 psi). He made an immediate precautionary landing and decided that the oil should be changed from W80 to W100. This was done and there were no more issues for a couple of years until last week! I was flying and the oil pressure dropped from the normal 40 – 45 psi to 30 psi. I made an immediate precautionary landing and called my engineer. He sought advice from a NZ engine builder and it was suggested that the oil pressure relief valve (Which does not have any adjustment) should be looked at. This was pulled out and cleaned, put back and test flown. The engine performed flawlessly with the pressure around 40 – 45psi once again.

Before we start worrying, I thought that it would be prudent to contact the experts for their thoughts. There may be old time 0 200 engineers out there that have experience with these engines and have encountered similar issues..

Someone mentioned that the oil pump was worn and in need of fixing which is a major. If it was, you would think that the problem would incur all the time.

Any thoughts out there would be greatly appreciated.

Cheers, Gordon

 

[Dan Thomas]

Someone mentioned that the oil pump was worn and in need of fixing which is a major. If it was, you would think that the problem would incur all the time.

That's a common problem with the small Continentals. It can't keep the pressure up with so much internal leakage in the pump. The other major problem is oil leaking out of the pump when the engine is shut down for some time; the pump cover plate fits metal-to-metal on the pump cavity, and it gets warped from the pressure and from being overhauled, and it will let the oil out, leaving the pump dry and unable to suck oil up out of the sump. Your engine gets no oil after it starts, and major wear happens to the bearings. That might be what's happening on your cold mornings, especially with W100. Put some W100 in a cup and leave it in the refrigerator overnight, then try to suck it up through a straw. Interesting. And your pump has to deal with that. If those bearings don't get oil real quick, they wear and you'll see permanently lowered oil pressure and a short engine life.

From Continental's M-0 publication: http://pceonline.com/wp-content/uploads/2017/04/M-0standardpractice2017-01-15.pdf


See those oil grades? SAE 50 is aviation 100, or W100. SAE 30 is Aviation 60, or W60. Even 80 is too heavy for cold mornings.

You might be better off with a multigrade like Phillips 20W50. Aeroshell's 15W50 is good but has an anti-scuff additive that might make your starter clutch slip. Approved oils from the Continental publication:

 

[Gordon Low]

That's a common problem with the small Continentals. It can't keep the pressure up with so much internal leakage in the pump. The other major problem is oil leaking out of the pump when the engine is shut down for some time; the pump cover plate fits metal-to-metal on the pump cavity, and it gets warped from the pressure and from being overhauled, and it will let the oil out, leaving the pump dry and unable to suck oil up out of the sump. Your engine gets no oil after it starts, and major wear happens to the bearings. That might be what's happening on your cold mornings, especially with W100. Put some W100 in a cup and leave it in the refrigerator overnight, then try to suck it up through a straw. Interesting. And your pump has to deal with that. If those bearings don't get oil real quick, they wear and you'll see permanently lowered oil pressure and a short engine life.

From Continental's M-0 publication: http://pceonline.com/wp-content/uploads/2017/04/M-0standardpractice2017-01-15.pdf

View attachment 109327
See those oil grades? SAE 50 is aviation 100, or W100. SAE 30 is Aviation 60, or W60. Even 80 is too heavy for cold mornings.

You might be better off with a multigrade like Phillips 20W50. Aeroshell's 15W50 is good but has an anti-scuff additive that might make your starter clutch slip. Approved oils from the Continental publication:

View attachment 109328

Thanks Dan, much appreciated.

 

[Magman]

I agree with Dan’s comments. I did not see any mention of preheat being used .
That may help the issue and prolong engine life.

It’s also possible that you really have oil pressure but a zero reading. There is a fitting on the Case with .020 (?) orifice that oil passes through enroute to the gage. The line from the case to the gage has no oil circulation. Hence it’s possible that the line may be filled with the same oil as when built. I’ve seen the line filled with congealed oil that results in oil pressure increasing slowly. Easy to address by cracking the line loose at the rear of the gage while the engine is running. It can get messy so plan ahead.

The engine does not need to be majored to address the Oil Pump itself.
Removal of the Accessory Case is not that difficult. The issue I find is that the wear is not on the Impellers but the Accessory Case itself. Older Cases were Magnesium which complicates repairs. There is a place that repairs them but it’s not cheap. The last one I met resulted in the Acc.Case being replaced. There were none available at the time that caused a 6 month wait. Note that if you have a Wet Vacuum Pump a new unit will likely not have the boss for oil return unless you specify.

If the gage reads zero - Believe it! Pressure should come up within 30 seconds.
If not; oil has left the Impellers as Dan said. There are various methods that can be used to reintroduce the oil to prime the Pump. Learn the and see the best way for you!

 

[Dan Thomas]

It’s also possible that you really have oil pressure but a zero reading. There is a fitting on the Case with .020 (?) orifice that oil passes through enroute to the gage. The line from the case to the gage has no oil circulation. Hence it’s possible that the line may be filled with the same oil as when built. I’ve seen the line filled with congealed oil that results in oil pressure increasing slowly. Easy to address by cracking the line loose at the rear of the gage while the engine is running. It can get messy so plan ahead.

I've drained that gauge line and put 5606 in it. That oil stays fluid at very low temps and you get a reading real quick. There is very little movement of the oil in that line, so mixing is minimal.

If the gage reads zero - Believe it! Pressure should come up within 30 seconds.
If not; oil has left the Impellers as Dan said. There are various methods that can be used to reintroduce the oil to prime the Pump. Learn the and see the best way for you!

There are STC'd oil system primer pumps. I made a manual one for my A-65 in my homebuilt. That pump would not suck if the engine had been shut down for a day or more. New accessory cases for that engine are nonexistent.

The real problem is maybe a worn pump cavity, but more likely the heavy oil in a cold climate, with no preheating. Even with preheat, W100 is too heavy for winter.