Shutting down - Round engine edition

[Salty]

For me, this procedure is a bit magical. I'm flying an engine and aircraft with no POH, so the smarties can leave that out of the equation.

Short form of my procedure is to run the engine up lean for 10 seconds - supposedly to scavenge oil into the oil storage tank and clean the plugs, reduce RPM, shut off mags, smoothly open throttle to full.

My engine is configured by design to not shut off via the mixture.

My question is really around the "scavenge oil into the storage tank" part. Can anyone explain how that works? How does higher rpms "scavenge" oil? What exactly is going on here?

 

[Skymac]

What engine?

I’ve done both in Lycoming’s and Continental’s but honestly see no difference via running up before shutdown, or not. I just taxi in lean, yank the mixture and once it stops, turn the mags off. The next hot, or cold start is always reliable and I see no difference in the clean kit on the Lycoming, or pulling the prop around.

I’ve always read this though as well.

 

[Salty]

What engine?

I’ve done both in Lycoming’s and Continental’s but honestly see no difference via running up before shutdown, or not. I just taxi in lean, yank the mixture and once it stops, turn the mags off. The next hot, or cold start is always reliable and I see no difference in the clean kit on the Lycoming, or pulling the prop around.

I’ve always read this though as well.

Housai Hs-6a

 

[jbDC9]

My knowledge base is various dry sump Pratts and Wrights, dunno how this compares to the Housai; the odd shaped yet kinda round thingy at the 6 o’clock position on these engines is the oil sump; some engines (R-1820/2600) have a front/rear sump. The purpose of these is to collect the “used” oil after it’s done its job lubricating the engine. There’s a vertical gear driven shaft with an impeller at the bottom of the sump that pumps this used oil out of the sump, back through the oil cooler and then return to the tank to start the flow over again. At higher engine speeds this scavenge pump does an efficient job at returning the used oil, but at idle or low taxi RPM it doesn’t have the volume, so oil will collect in the sump and not get returned to the tank. So, prior to shutdown, we run the engine up to 1200-ish RPM for 30 seconds or so to get the scavenge pump turning and the oil back to the tank, then shut ‘er down. With the mixture of course!

 

[Salty]

My knowledge base is various dry sump Pratts and Wrights, dunno how this compares to the Housai; the odd shaped yet kinda round thingy at the 6 o’clock position on these engines is the oil sump; some engines (R-1820/2600) have a front/rear sump. The purpose of these is to collect the “used” oil after it’s done its job lubricating the engine. There’s a vertical gear driven shaft with an impeller at the bottom of the sump that pumps this used oil out of the sump, back through the oil cooler and then return to the tank to start the flow over again. At higher engine speeds this scavenge pump does an efficient job at returning the used oil, but at idle or low taxi RPM it doesn’t have the volume, so oil will collect in the sump and not get returned to the tank. So, prior to shutdown, we run the engine up to 1200-ish RPM for 30 seconds or so to get the scavenge pump turning and the oil back to the tank, then shut ‘er down. With the mixture of course!

Most of what you described applies to the Housai as well. That helped, thanks.

 

[Magman]

My understanding has been that the Scavenge Pump could move a greater

volume of oil than the Pressure Pump. IIRC there was no procedure

addressing the issue on the R-2000.