Airplane engines seem to have their individual preference for oil level. Forcing more oil into the sump only results in it being blown out the breather and wasted while oiling up the outside of the plane. It does nothing useful. There should be a point where the oil level stabilizes for some time. That's your target and the engine's happy place. It will not be the Maximum fill mark. If there is no "happy place" for your engine then the oil is going somewhere that it shouldn't. That's unlikely to happen on both engines.

Hi John,
Yes, I agree. I learned that early on in my ownership If I put in 13qts, I end up oiling the outside of the plane. I put in 12 for the oil changes and it slowly blows it out until it gets down to 10qts Which seems to be the happy place for both of my engines. Stays pretty steady until its due again. Hence my curiosity how it works out for Jeff.

For roughly the first 15 - 20 hours of my usual 25 hours oil life span, both engines will stay at or close to 13. For the last 5 - 10 hours, the right engine will burn a bit (my usual flight is 2 - 3 hours...it'll usually burn a quart...I've seen it burn 2 on a flight that was about 4 hours at the very end of the cycle). The left engine will burn very little under any circumstances, I've never put in more than half a quart.

For the flight in question, I checked the oil the next day in the hangar. The right engine was down one quart, the left was basically at 13 (call it 12.75?).

I've been using Aeroshell 100 since I've had the airplane as my recurrent training shop recommends for the long and hot summers in Texas. However, they also recommend 20W50 for colder months...which I did not do before this trip, but perhaps I should have.

I appreciate all of the feedback so far, thank you.

Norman has nailed the explanation. TAS / Twin Cessna Flyers has written about this.

It happened to me only once during my twelve years of 421 ownership.

Best,

Dan

: Re: Non-congealing Oil CoolerPostPosted: 25 Nov 2018, 09:36
Offline. FROM JESSE HERCULES


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Ok, let’s review.

Your Vernatherm valve senses temperature and controls oil flow to the oil cooler. If the oil is cool, the vernatherm closes and the oil bypasses the cooler. When the oil reaches say 180 dF the vernatherm opens and lets oil to the oil cooler.

The original type of oil coolers in airplanes were the congealing type. Also, single weight oils were the only choice. So it could happen that when the vernatherm opened the oil would try to flow... and get totally blocked by a fully congealed bunch of very cold single weight oil plugging the oil cooler. The oil in the cooler was not moving, it was just sitting there. But the oil cooler was getting blasted by cold air and so the oil got very cold. This was a serious problem. The engine needed cooling, but it was not getting any. It was like not having an oil cooler at all in the winter.

The designers in their wisdom had a solution. Let a little bit of oil bypass the Vernatherm and ALWAYS flow though the oil cooler to keep it from getting cold enough to congeal. Even when your vernatherm is fully closed, some oil gets cooled. This may cause your oil to run a bit too cool and accumulate moisture, but that’s a long term problem. It’s a maintenance problem, not a safety of flight problem. The designers avoided the BIG, immediate problem of congealed oil coolers causing oil overtemp and causing lack of cooling to the engine...a safety of flight issue.

Now in the meantime multi weight oils are invented and become widely used. They flow just fine when cold, they are MUCH harder to congeal.

So where are we now?

I run a multi weight oil in a Bo with a non congealing oil cooler. No big safety of flight issues, tape or no tape. With no tape, my oil does run a bit cool, which could cause moisture and rust over time. So I tape about 2/3 of the oil cooler to keep temps up in the winter. Essentially, I am reducing the amount of cooling that happens to the oil that is bypassing the vernatherm. So even though there is always some oil running through my oil cooler... that oil does not get a lot of airflow and it stays hot all the way through. It accomplishes the purpose of Non Congealing while also avoiding the problem of excessive cooling. Best of both worlds.

For Stu, if you have a congealing oil cooler, I’d really recommend a multiweight and a good whole engine compartment preheat for winter flying. And partially tape the cooler if that’s what you need to keep the vernatherm open. The idea is, Vernatherm open from takeoff to shutdown, or at least to cruise. Keep some oil flowing at all times.

Maybe, and I’m not sure about this... having a modern multiweight oil could mean you never need to tape a congealing oil cooler. In that case it would be simply unnecessary... the vernatherm could open and close as needed and the oil would always flow through. I don’t know that the new oils are that good, and what the min temp for that strategy is. Might work in Indiana but not Fairbanks, not sure.

I forgot to answer one question about power settings. I was cruising at 31" that day (normal), and I left that power setting in through the descent. I usually start to slowly pull back 1" per minute at something like 8 - 10 minutes from landing, usually stopping at 25" until short final.

To directly answer the question: when the oil pressures dropped (and temperatures rose) during the descent through the cold layer of air, the power setting was cruise setting, I was not changing the power.

Thanks Jeff! I’m always interested in knowing how other owners fly their 421’s. I’m no expert but, I’m pretty confident that your temp/press anomaly wasn’t pilot induced in anyway. These other guys know waay more than I do, especially about things like the vernatherm valve, (which I knew nothing about prior to this conversation). BT is a great place to learn new things! Thanks for your inquiry here.
John

Ditch the single grade oil. If you really want a single grade at least use W80 in the winter. If you want to get an idea of what your oil pump was trying to force through the cooler, put a quart of W100 in your freezer (which is about 0°F)overnight and then try to pour it the next morning.

I don't know how you are keeping it at 13 quarts. That was not possible on my 421. It would throw at least 2 quarts out during the first hour or so if I did that. It liked 10-11

Given that you have to be putting a lot of oil thru it I wonder if vents are clogged. But I like the theory above as well.

Not an expert by any means I only have about 400 hours in a 421. Your SOP sounds good to me.

I only ran 100 in the summer and multi viscosity in the winter.

Mike

You can fill to 13 quarts, fly for an hour, land and the oil will be 12 quarts.
It can take a couple of days for that last quart to drain down to the sump.

At an oil change fill to 13 and run down to 10. Then add a quart.

Jack, 228 KTAS on 23gph/side with cool CHTs? Is this normal? Very impressive.

Not to speak for Jack but, those numbers are typical for those altitudes (in my experience).

Not to speak for Jack but, those numbers are typical for those altitudes (in my experience).

Never had a similar oil pressure issue in 421s, so I’ll defer to others to comment about that.

However…



Why?

I usually kept power up until pretty close to the airport and/or I needed to slow for some other reason (redline, traffic, etc).

The 1”/minute thing doesn’t do anything to help the engine.

Robert

That 1” per minute power reduction is an OWT!!!! Common sense applies here. Smooth power changes and gradually reduce power when close to the airport.