Continental low oil pressure

[DonMuncy]

My 231 (Continental TSIO 360 LB) suddenly developed low oil pressure. When I started it this morning, the pressure ran up about mid-scale when it usually goes up to about 2/3s to 3/4 scale when cold. (But I thought perhaps the weather is a little warmer than it has been). After warm up, on run up, it only moved barely up into the green. After take off, on original reduction in power, the pressure dropped into the yellow.

I returned and landed. At any speed nearing idle the pressure dropped to the very bottom of the yellow.

I removed the cowl, removed the oil pressure transducer and replaced it with a mechanical gauge. On firing up the engine, it showed approximately 30 psi at 1500 to 2000 RPM.

I felt better, thinking the transducer was probably bad. But checking the maintenance manual, yellow runs from 10 to 30 and green runs from 30 to 80.

Obviously the pressure is low.

It seems far fetched that the engine would suddenly develop sufficient bearing clearances to substantially decrease oil pressure. (Bear in mind that the Continental "reads" oil pressure at the downstream end of the oil flow, rather than immediately after the pump, as Lycomings do.)

It seems possible that some debris in the oil is holding the pressure relief valve open.

Can anyone think of any other reason. Anybody experienced this particular problem.

[Will W]

Did you replace the oil type recently with mineral oil do to a cylinder change? Or are you mixing oil types.

[DonMuncy]

It had a cylinder (overhauled) replaced 40 or so hours ago. It had an annual 6 to 10 hours ago, and I'm not certain what oil they put in, but I'm virtually certain not mineral oil. I have not added any since then.

[bonal]

I would definitely contact the shop and check on the oil type. Darn annuals. Hope it's some thing simple

[DonMuncy]

OK, you caught me. I got off my duff and checked my logs. They used Aeroshell 100,the same as I always do.

[jetdriven]

Could be debris holding the pressure relief valve open and dumping pressure. Investigate that.

This is for the -RB. Yours should be similar. http://www.redskyventures.org/doc/cessna-maintenance-manuals/Continental_TSIO-360-RB_Maintenance_Manual_1996.pdf

[Will W]

On a cylinder overhaul, you should be doing a oil change at 25 hours and if everything is good on the engine and oil, then taking it off mineral oil is ok.  I'm trying to follow here... Your cylinder replacement was aeroshell 100 (mineral oil)?  Then at the annual, did they take change the oil (should be around 25 hours)?  If they find no problems in the oil, filter, and cylinder leaking, then they usually take it off aeroshell 100 (mineral oil).  Are you saying though that you always use aeroshell 100 which is the mineral oil?  I didn't know people usually operated with mineral oil.

[triple8s]

There is Aeroshell W100, Aeroshell W100 plus, and Aeroshell Oil 100 MIneral Oil ( has a blue stripe on the bottle ). I have seen folks use the Mineral oil (the bottle with blue stripe) during cylinder break in and change to the aeroshell 100 or other oil after break in.

[Guest]

Don,

I'm sure that Byron is correct, there is a particle stuck under the relief valve. Simply removed the valve and clean the plunger and the seat, reinstall with a new gasket and run the engine again.

Clarence

[aaronk25]

Relief valve....great idea. Mineral oil is not required. That's from the old days.

[Yooper Rocketman]

I agree with Brian and Doc.  Most likely debris in the relief valve.

[DonMuncy]

Great news. As I, Byron and others (including a Continental rep), hypothesized, it apparently was something stuck in the pressure relief valve causing my low oil pressure. Naturally, when I, er, my hangar elf, removed the relief valve, it popped out and fell on the asphalt floor, so I couldn’t see what might have been in there, but cleaning up the seat, plunger, etc. and reassembling solved the problem.

While I was at it, since I had to get a new crush washer, I replaced the spring as well, and my oil pressure is a little higher than before.

Perhaps of interest to other 231 owners, the engine manual indicates the relief valve is adjustable and has an inner and outer spring. Mine is an “older” model having one spring and no adjustment.

This valve is a little hard to access, and re-compressing the spring while assembling is very difficult. I finally devised a fixture to get the job done. If anyone else runs into this, let me know and I may be able to save you some time.

Thanks to everyone for the input.

[chrisk]

I'd love to know where the pressure relief valve is. I also have a 1982 231.

[DonMuncy]

It is on the accessory case on the pilot's side, under and just to the rear of the oil filler tube. If it is like mine and has the non-adjustable type valve, it is a brass dome shaped nut, 1 1/8 inch. It will be safety wired to the accessory case.

[chrisk]

I'll have to look for it when I get my plane back from its annual. Thanks!

[N231BN]

http://www.continentalmotors.aero/Support_Materials/Publications/Illustrated_Parts_Catalog/

 

Put in your serial number or go through the menus and then click accessory case. It will give you a nice drawing as well as all of the parts in it with estimated costs.

[smccray]

Don-

 

Glad you got this solved.  Sorry I missed you on Saturday morning!

[Mikey]

Very helpful. I am going through this right now. Hopefully new spring and a clean seat will fix the issue. Thanks!

[Cardinal767]

I just bought a M20K in 08/2015 with 1400 hours on the engine. The oil pressure would drop in flight but would still be just in the green. I pulled the relief valve out to check the plunger for possible debris being the aircraft had longs period of not flying before I bought it. What I found was that the spring on the relief valve plunger was worn to half it's normal diameter in the middle of the spring. No way was it at full strength. I replaced it and have no problems since with the oil pressure dropping. High oil consumption (1 quart per 3-4 hours) on the other hand is still an issue, but it does have 1530 hours on the engine now. 

[Jsavage3]

On April 2, 2015 at 3:17 PM, DonMuncy said:

This valve is a little hard to access, and re-compressing the spring while assembling is very difficult. I finally devised a fixture to get the job done. If anyone else runs into this, let me know and I may be able to save you some time.

DonMuncy,

Would you mind sharing this technique...I'm about to replace my spring.

Thank you,

Jsavage3

[DonMuncy]

Attached is the device I put together. There is a motor mount tube just outside the valve one can clamp this device onto with a C-clamp. Then screw the rod in carefully to push the "dome type" nut into position while turning it to engage the threads. The other thing is a wrench to do that turning, as there is quite limited space available. I don't remember the size of the socket, but it will be apparent what sizes will be appropriate. It is large enough to push on the dome, but not big enough to actually fit over the nut flats. You can't see it, but there is a nut inside the socket to hold it to the rod.

Glad to elaborate further if this doesn't make sense.

[BDPetersen]

At the risk of stating the obvious, I hope all who are dealing with debris in the relief valve are thoroughly checking for metal in all the screens and filters. My similar experience was on an IO-470D which had a broken ring and made metal resulting in a tear down inspection.

 

[jlunseth]

You got the problem solved Don, which is great.

For reference, I run Philips XC, have a JPI 930 doing the measuring, and OP of 38-45 is normal.  That's where it sits pretty much all the time in cruise once the engine and oil are warm.  It might drop a pound or two below that on a warm day, butiIf it drops below 34 I start wondering.  

I burn so little oil in my 231 I can often go from one oil change to the other without adding.  About a quart in 25 hours.

Edited April 24, 2016 by jlunseth

[Jsavage3]

Does my bird have a problem? I had my oil press relief valve spring & plunger replaced as well as tried adjusting (increasing pressure) the oil pressure itself...all with no change. I'm still seeing about 40 psi in cruise flight and well down into the yellow (estimate 10 psi) after landing and taxiing in with 800 to 1000 RPM. The oil pressure responds immediately to an increase in power with the throttle. Side note...the oil was changed and the filter was clean.

Now what? Any ideas? Live with it as in that's normal for a 252?

Informational...1175 TSN, 375 SMOH and no engine monitor so my indications for from a peanut gauge...

I'm thinking check the gauge for accuracy. Thoughts?

Install an engine monitor...I know, it's on my list...

Your input is appreciated. 

Edit...I run Phillips 20W50 with Camguard and I keep my oil quantity between 6 & 7 quarts with my POH telling me 5 quarts min for flight...

Edited June 29, 2016 by Jsavage3
Type oil and quantity comments

[DonMuncy]

In my opinion, this is perfectly normal for the Continental engine. In the yellow in cruise would really get my attention, but taxi and idle is perfectly alright. This is from what I have read, folks I have talked to and my experience. I don't issue guarantees and I'm not an expert.