O-300 Recommended oil level

[Fearless Tower]

Curious what the ideal or recommended oil level is for the O-300 in a 170.

max capacity is 8 qts, but I have not seen any recommended min quantity, or documented 'normal' level. The previous owner told me that about 6 was normal on the ground.

Any recommendations would be helpful. The '48 Owner's manual and O-300 manual are pretty vague on this.

Thanks,
Andrew

[GAHorn]

The Owner's Manual recommends minimum of 4 qts for operation for a landplane, and 6 qts for a seaplane.
I have found that more than 7 qts in a landplane results in excessive blow-by and loss of 1 qt which stabilizes around 6 qts. I therefore keep mine at 6 qts and carry a spare in the bag compt. There are those who believe more is better for oil cooling,...which may appeal to the logic... but I have seen oil temps remain the same regardless.

[Fearless Tower]

The Owner's Manual recommends minimum of 4 qts for operation for a landplane, and 6 qts for a seaplane.

George,

Is that the in the OM for the A or B model? I would imagine that it would be the same for the '48 since it is the same engine, but I haven't found that detail in my OM.

Thanks,
Andrew

[bagarre]

C-125/C-145/O-300 Service Manual states

Oil Sump capacity (all models) 8 quarts.
Minimum oil supply at any time (all models) 4 quarts.
Oil Consumption (all models) 0.017 #/BHP /hr

I see the same behavior as George. My O-300-D will blow the first quart out very quickly and settles down at 6 1/2 quarts.

[rupertjl]

Can someone check my math?---

0.017 lbs/HP/HR

Lets use 75% rated power on a 145 HP engine gives 109 HP

0.017(109)=1.853 lbs/hr

Density of Aeroshell 80W @ 15 deg C is .892 kg/L converted to 1.86 lb/qt

So 1.853 lbs/hr divided by 1.86 lbs/qt equals 0.996 qts per hour as max oil consumption at 75% power

It's 1.3 qts at rated power! I was worried about my oil consumption but I guess not now!

v/r,
Jud

[jrenwick]

I have O-300A engines in both my 170B and my Swift. I keep the 170 at 6 quarts, but I keep 8 in the Swift because it runs hotter than the 170. I've seen no tendency of the Swift to blow out the top quart, so this might have something to do with how healthy the rings and cylinders are in a particular engine.

I think the theory is not that the engine will run cooler at cruise with more oil in the sump, but that it will take longer to raise the temperature of the oil (e.g. during a climb) because there's more of it to heat up. More oil will also take longer to get to operating temperature after starting on cold days, so that might be a disadvantage for some. It might make sense for some to use the 8 quart level in the summer, and six in the winter.

[ptporebski]

I have a O-300A model in a 59 C-172 and have noted the same oil level. The engine likes to be around 6 qts. More than that and it dumps it overboard resulting in a oily belly. At 6 qts. I find it burns a qt about every 4 hours or so regardless of the power setting.

Pete P.

[DavidBlom]

This is interesting - the fellow who owned my 170A before me said to fill it to 7q and put another quart in when it gets down to 6. I never let it sit at 6 quarts, but in light of this discussion I'm going to give it a try & see how quickly it drops to 5 1/2. One thing I do know is any amount over 7q is out the breather and all over the belly in one short filght.

Dave Blom
1950 C170A C-FNIE

[bsdunek]

I have O-300A engines in both my 170B and my Swift. I keep the 170 at 6 quarts, but I keep 8 in the Swift because it runs hotter than the 170. I've seen no tendency of the Swift to blow out the top quart, so this might have something to do with how healthy the rings and cylinders are in a particular engine.

I wonder if all 145 Swifts are like that? In my experience, all 170's blow out the first quart quickly. Maybe differences in the installation?

[n3833v]

I keep mine at 6 qts also. I found years ago that oil beat by the crank tends to vaporize and lose oil until a certain point that will stabilize and basicly stay there for ever except for consumption.

John

[GAHorn]

Can someone check my math?---

0.017 lbs/HP/HR...So 1.853 lbs/hr divided by 1.86 lbs/qt equals 0.996 qts per hour as max oil consumption at 75% power

It's 1.3 qts at rated power! I was worried about my oil consumption but I guess not now!

v/r,
Jud

The only part you got incorrect was assuming you'd ever be able to generate "rated" power.

This engine only makes "rated" power of 145 hp at 2700 RPM...which probably means that with approved props it will only occur in a dive!

As for the approx. 1 qt per hour permitted by Continental.... YES! That is their standard for virtually ALL their horizontally opposed engines. Obviously, very few operators would stand for that, however....it probably keeps Continental from having to warranty too many new engines!

[jrenwick]

I have O-300A engines in both my 170B and my Swift. I keep the 170 at 6 quarts, but I keep 8 in the Swift because it runs hotter than the 170. I've seen no tendency of the Swift to blow out the top quart, so this might have something to do with how healthy the rings and cylinders are in a particular engine.

I wonder if all 145 Swifts are like that? In my experience, all 170's blow out the first quart quickly. Maybe differences in the installation?

This may be important. Corroboration at [url]( broken link)

3. Engine breather exposed to low pressure. Ensure the location of the engine breather is in the precise position as specified by the airframe manufacturer. If the end of the hose is exposed to airflow in an area of low pressure it sucks a mist of oil from the crankcase.

[GAHorn]

I have a great deal of respect for Sacramento Sky Ranch and most of their opinions... but this one does not bear fruit.

A breather line which exits to a low pressure area will evacuate the breather efficiently....exactly as it should! But unless the engine is pumping oil out the breather....it will have NO effect on oil consumption...and if the engine is pumping oil out the breather, ...the oil will exit the engine regardless. This statement of theirs is without merit, in my opinion.

[jrenwick]

I have a great deal of respect for Sacramento Sky Ranch and most of their opinions... but this one does not bear fruit.

A breather line which exits to a low pressure area will evacuate the breather efficiently....exactly as it should! But unless the engine is pumping oil out the breather....it will have NO effect on oil consumption...and if the engine is pumping oil out the breather, ...the oil will exit the engine regardless. This statement of theirs is without merit, in my opinion.

In the 150 Aerobat, Cessna, in effect, moved the vent inboard toward the center of the crankcase (nice photos at http://luscombe.org/index.php?page=modi ... l-breather. Other small Continental users have found that this mod can clean up the breather output significantly. That suggests that we're not talking about a uniform oil mist, but a flow of oil over the inside surface of the crankcase in that area. Does increased airflow help to move that oil toward the outlet? I don't know, and I suspect it's in the realm of black magic.

Maybe SAC Sky Ranch knows of experience with relocating the breather pipe to reduce oil emission. I'm in a mood to ask more questions about this, rather than rule anything out. What I do know is that I've got two different installations of the same engine type, and the one in the Swift holds eight quarts of oil happily without dumping it on the belly. I've never tried putting 8 in the 170, but maybe I'll give it a whirl and see what happens.

(Full disclosure: I'm dealing with this right now in my J3, trying to postpone a top overhaul if I can.)

[GAHorn]

John...which exact engine do you have in the Swift...and which exact engine do you have in the Cessna...and what differences exist in their vacuum and breather systems?

Minor differences can give different results. Even in the same exact installations... major differences can exist based upon engine health. An engine with worn rings might have a lot of ring-blow-by which pressurizes the crankcase and helps oil leave.... A leaking prop-shaft/crankshaft seal can pressurize a crankcase with the same effect.... A breather line that is full of crud...versus a clean line... One that is routed differently, or has a seperator installed, ...etc. etc. etc.

ALL breather lines should exit to a lower-pressure area than that found at the source.

The C-150/O200 breather fitting has been shown to be a good solution for that airplane...but it is not approved for the O-300 engine to my knowlege. (Internal clearances need to be assessed. Also, that fitting can be made in the field by silver-soldering or brazing a short tube into the end of the fitting.) The O200 crank throw slings oil almost directly at the breather crankcase-exit and provided plenty of oil to the breather-line. OIl which subsequently flowed down the interior crankcase wall would be pushed out the breather line.
The "aerobatic" fitting basically is an alteration....one that behaves like a "standpipe" to reduce the ability of the oil to flow into the line without restricting the flow of air. (There needs to be an exit of crancase gases to atmosphere in order to avoid rupturing other accy-seals in the engine.)