Oil Consumption UP - WWYD?

Lance F

Lance F

En-Route
PoA Supporter
Joined
Apr 9, 2005
Messages
2,897
Location
GA
Display Name
Display name:
Lance F
The Lycoming IO-360A3B6D in my Mooney is a little under 700 hours SMOH in May of 2002. From the beginning the oil consumption was a consistent 12 hours per quart. I was ok with this.
Starting in about May of this year the oil consumption has increased about 1 hour per quart per month, and now is only about 5 or 6 hours per quart. Something changed.
A compression check shows all four cylinders at 74 or 75 /80. Since the exhaust pipe has a a nice dry tan coloring on the inside and since the bottom of the plane seems especially oily, I assume the oil is leaving via blowby.
We'll have access to a good boroscope shortly and will take a look inside the cylinders. Other than that I am open to ideas as to how to isolate this problem.
Would anyone have any problem flying the plane until the cause is disagnosed and fixed?
 
The IO-360A1B6D in the Cardinal RG I used to fly did something similar -- I reported to the owner that I was seeing about 6 hours per quart when she was used to about 10. We also believed it was blowby, but it was one of the reasons I hesitated buying the airplane when she put it up for sale, as I thought I'd noticed a trend toward even higher consumption.

I'm not a mechanic and didn't sleep at a HIE last night, but I'd probably still fly it. Maybe not over open water though.
 
Could it be blowby? I used to see it on the tsio-360 andthe gtsio-520. Both I would run at 2 quarts low. What level are you filling to on the stick? How does the belly look?
 
Every one must remember the compression has nothing to do with oil consumption.

oil consumption is controlled by the oil control ring at the bottom of the piston. The compression is determined by the three compression rings at the top of the piston.

short of topping the engine, there isn't much you can do about oil consumption.

High oil consumption can be caused by worn valve guides also.
 
Lance F said:
The Lycoming IO-360A3B6D in my Mooney is a little under 700 hours SMOH in May of 2002. From the beginning the oil consumption was a consistent 12 hours per quart. I was ok with this.
Starting in about May of this year the oil consumption has increased about 1 hour per quart per month, and now is only about 5 or 6 hours per quart. Something changed.
A compression check shows all four cylinders at 74 or 75 /80. Since the exhaust pipe has a a nice dry tan coloring on the inside and since the bottom of the plane seems especially oily, I assume the oil is leaving via blowby.
We'll have access to a good boroscope shortly and will take a look inside the cylinders. Other than that I am open to ideas as to how to isolate this problem.
Would anyone have any problem flying the plane until the cause is disagnosed and fixed?
Click to expand...

Are you doing oil analysis? A sudden change in consumption might show up as increased metal in the oil.

One thing you can do is check the crankcase pressure. A trick I've heard of is to get a spare oil filler cap and attach a hose barb fitting. Run a hose fro there to an old ASI and see what the "airspeed" reads at full power. I don't remember what's considered "normal" but I think it's something like 1.5" H2O which can be translated to IAS.
 
Last edited:
I put a heavier weight oil in my tractor when it started doing this.....but I know its only time.
 
We're seeing a similar trend in our IO-550, with 1800 SNEW and 1100 STO. We're now somewhere between 3 and 4 hrs per quart.

We're running between 5 and 6 qts which helped but didn't solve it.

Borescope inspections report signs of oil pooling and cross hatching worn on the even cylinders, valves normal color. Oil analysis by Blackstone have been steady and within normal range for engine time. Oil filter has minimal metal and carbon at change.

All the advice we've gotten agrees with Tom. Possible valve guide wear, probably worn or stuck oil rings.

At 3hrs/qt we are at the "threshold of concern". Basically we're hearing we should keep a close eye on oil analysis, filter with regular borescope and be ready for at least some cylinder replacements.

I don't know if this will help you but you're not alone.

Joe
 
We had a similar situation on the 231 (TSIO-360-LB1) which was caused by bad pushrod seals. We replaced them and it seemed to fix the issue as there was no residual oil residue on the nose gear door and oil consumption was back to normal.
 
Last edited:
Appreciate the comments. There is no oil leaking anywhere, so I'sure it's not that. Oil analyses (every oil change since SMOH) show no metal changes. If I were burning it because of oil control rings or valve guides (as opposed to being blown out), wouldn't I see evidence of that in the exhaust pipe? Ikeep the oil at 6 quarts like I always have.
I guess I'll have to work on getting that boroscope.

If I can isolate one cylinder as being the culpret, I'll pull that one. However, I am not going to do the whole top end to save a few courts of oil.
 
Lance F said:
If I can isolate one cylinder as being the culpret, I'll pull that one. However, I am not going to do the whole top end to save a few courts of oil.
Click to expand...


Watch your plugs, they will show you which cylinder it is.......... if it is just 1
 
Greg Bockelman said:
Wet??
Click to expand...


Why? Blowby indicates that the crankcase is getting pressurized by one or more of the cylinders. I assume by exhaust gases getting by the piston rings. Wouldn't a wet plug indicate oil getting into the cylinder not exhaust gases going out via the wrong path?
 
Lance F said:
How will a plug indicate blowby?
Click to expand...

If it is blow by, that much oil will be all over the aircraft, belly/nacelle or ?

If it isn't blow by, it will be burning it, and the plug will show a lot of very black deposits, and may be wet/oily
 
Lance F said:
How will a plug indicate blowby?
Click to expand...
It might not be blowby. Engines lose/use oil three ways: Out the breather due to high crankcase pressure, Burned in the cylinder due to oil control ring issues and/or loose valve guides, and external leaks. Like Tom said earlier, blowby is a function of the compression rings and a problem there ought to be detectable with a compression tester. If the oil control ring is allowing oil to remain in the cylinder or oil is leaking into the cylinders along the valve guides, chances are the lower plug will be very oily when pulled and if the problem is really bad the top one will show evidence as well.

One thing I meant to mention earlier is you can get a overpressurized crankcase if the front crank seal is worn or the oil filler cap (or dipstick) doesn't seal well. Both are easy fixes.
 
You must log in or register to reply here.
Back
Top