So my Beaver/Pratt 985 friends, I have a chronic wet belly on my beaver. Stay out of the gutter..........if you can.

Here's the situation. On amphibs. 790hrs smoh-Covington. Compressions all good, 75/80 or better. This airplane has lower induction. There doesn't seem to be any sort of leak, or at least not one that can coat/baste the belly on 30 minute flight.

During initial cold start up, if the plane hasn't run for a couple days there will be oil spray from the exhaust from sitting. After warm up I shut down and clean that off before flying. After any kind of flight upon shutdown, there will be enough oil (i know a little goes a long ways) to be dripping off the aft cowl lip and everything behind there. It appears to me, that it's being blown out the crankcase breather exhaust. It also seems to draw via low pressure some of the oil about a third to halfway up the firewall. Also, when I do the warm up, I will also do a mag check and bring the RPM up to 1750. After shutdown the exhaust stack will be dry just like after any kind of flight.

The oil spread seems to favor slightly going down the right side vs the left, but it's not much.

The crankcase breather box has a quick drain behind the breather box exhaust, and I will get a little oil out of it, maybe up to an ounce, but usually less. I run the oil tank level around 4.5 gallons, maybe 5 if the flight is going to be over 2 hours. One thing that I'm thinking of doing is draining the oil tank to see if the dip stick is reading correctly. Remember, I'm on amphibs, and was curious if having the tail up gives the dip stick reading an erroneous reading? When it says I have 5 could I have 6 and it's just blowing it out? However, it would seem to me that a 985 having a separate oil tank vs sump wouldn't really care what's in the oil tank as long as there was oil for the pump to pump.

Do you have and use the rocker drain system? I realize that might be an issue on floats. I'm going to ask a friend familiar with Beaver's on floats and return.

Do you pull the prop through every cylinder before start checking for hydraulic lock? As far as measuring the oil if it is at the same angle every time after a flight check the oil 15 minutes after shutdown and again the next day/flight. If the same that is good. Knowing how much is in it by draining is a good idea, then you'll know what you have.

Breather vent outlet isn't out in the open? Is it inside the cowling?
P-51 is on the bottom of the Radiator Scoop and is a mod. Originally was on the R/H side of the cowling, earlier was on the L/H side of the cowling.
T-6 is on the R/H side of the cowling.

Being a radial it'll mark its territory.
Other consideration is the age of the O/H. The older it is the more oozing you'll have from gasket/parting surfaces as gaskets compress with time/heat/pressure.

TCDS sez oil Capacity is 6.24 US Gallons. 5.2 Imperial.
Looks like oil tank is fairly low compared to other warbirds. On those the oil in the tank can move into the crankcase over time. Don't know how much that'll happen with the lower oil tank.
A rocker oil retrieval system can help reduce oil in the crank case that can migrate into the cylinders while sitting. After shutdown you screw a fitting into a quick disconnect fitting on the bottom of the sump. That is connected to some kind of a jug with a hose to the screw in fitting. It drains oil from the sump. When you go to start up you dump the jug contents back into the oil tank. At start up it reduces oil you blow out the exhaust and oil that will drip onto the cowling.

Type of floats matters and the “throat”angle matters to the accuracy of the dip stick.

Are you checking and servicing before or after flights? The only time you can get an accurate reading is immediately after shut down. It is best to run a full minute or two at 1200RPM to get good scavenge before final shut down of the day. On a float plane you probably cannot do that scavenge run. If shut down is preceded by extended slow idle periods you are most likely shutting down with excessive oil remaining in the engine and over servicing the oil level.

My SOP on Warbirds (Radials and Inlines) and the PT-6 is level check at shutdown. We have a ruled Expense type notebook we track Hours/Use/Pilot and Oil Level for Trends and Quantity. Pancake Motors we track quantity at Preflight after it has dripped down into the case. We also crack the oil filler cap at shutdown to let moisture in the hot air escape.

It has been awhile since working on the 985 in Spartan Executive S/N 34, the last TW version built. But similar to the 1340. Things that can dirty things up on the lower end are scavenge tube hose clamps, Rocker Arm Cover Gaskets and cylinder interconnect hoses, Sump to Crankcase Gaskets and Rocker Arm Shaft Gaskets.

Nope, sure can't.

[youtube]https://youtu.be/AvWfbIe4X_4[/youtube]

If the blower seal is bad that makes a mess. There are ways to check this, but I cant say for sure how.

You need to find a Round engine guru. An old Ag cat guy.

They can help.

Push rod tubes and rockerbox gaskets are perpetual maintenance items, but the are usually pretty obvious.

If blower seal is getting worn you will notice white smoke puffing out exhaust after landing taxiing in and oil dripping from carb drain after shutdown.

If you see this it is time to remove from service because this indicates worn and failing blower shaft bearings. The blower “seal” is actually an aluminum plate with an extremely close fit hole in it for the blower shaft, not a rubber type seal.

I went through this on my engines a long time back.

last night I did a solvent rinse on the back side/accessory area and lower firewall and got most if not all residual oil cleaned up and did a ground run. I let engine idle until oil temp in the green, and then brought power up to essentially long range cruise power, 1900 rpm and about 25" MP. I let it run at this power for a few minutes until oil temp rose to a normal flying temp of around 75 degrees C.

My post run inspection revealed virtually nothing. My shutdown oil level was 4.5 gallons. While it was running at a high idle, 1200 rpm and at normal idle, 650-700 rpm, I observed no oil in exhaust and no visible smoke. Maybe the lower level of oil in the tank is helping?

I recently started doing the 1200 rpm thing before shutdown while on the ground. In the water that's not a realistic thing to do, at least not until tied well to a dock that is very secure to the bottom and shore. 1200 rpm creates quite a bit of thrust and could easily start to shift a free standing dock.

Do you have a wet vacuum pump going bad. They can put a lot of oil into the separator system.

Have any lower cylinders been replaced and the wrong piston installed with holes under the oil control ring?

Leakage by the lower valve guides when sitting?

See if the gasket at the rear of the oil sump connection to the engine case has not sucked in on one side.

Do you have the 45 degree deHavilland tube where the breather comes out of the right upper engine case. This fitting routes the breather tube upwards before it drops down towards the separator.

With NuChrome cylinders having sprayed silicone carbide coating that wears off during break-in I’ve wondered how oil gets to the top end after the coating is gone? The NuChrome process does not shock the bores to make the cracks like old Channel Chrome allowing oil to lubricate the rings. They look like a mirror finish.

If real bad maybe after it sits for a bit pull the lower exhaust Y stack and see if you can ID if the oil is coming around from one side of the engine or another?

Any different deposits visible between the cylinder spark plugs

Charlie, thank you for the things to consider. I'm going to put about 5 hours on the plane in the next few days. My oil tank service level checked warm is 4.5 gals. I flew the airplane last night off the runway and made a few takeoffs and landings. Upon shutdown there was still some oil just behind the breather exhaust stack, but it seems to be lessening with the oil service level lower. I will get a chance in the next few days to see how it changes as the oil service level gets closer to 4 gals. If that doesn't seem to be helping, then more of the above will start to be looked at. Fortunately I have a good 985 man in Joe Quint on the field and will be able to dig deeper.

If oil is draining into the engine from the tank at high level replace the O ring above the oil screen. The oil tank is low in the Beaver so it’s not as pronounced as a high mounted oil tank like in a Beech 18.

With the oil screen out reach inside the accessory case and pull down on the center spring shaft and the check valve assembly will pop down. I had this trouble a few months ago and replacing the ring helped. Check the valve surface is clean and can hold some gasoline once clean.

23435 O ring is available from Sun Airparts or the R-985 overhaul shops and others.

I believe there is a MS equivalent also MS28775-225 but the Orange silicone O ring above
seems like a better idea.