Manually pulling prop though in cold weather

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JOhnH

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Down here in Florida, this doesn't come up very often, but in the Cold Weather Operation section of my POH, it says "Always pull the propeller through by hand, opposite the direction of rotation several times . . . "

Why the opposite direction and what is the danger of pulling it through in the normal direction?

We are flying the Bo up to Ocoee TN next weekend and the temps are predicted to be in the low '20s at night, :hairraise: :eek2: so I am trying to figure out how people fly in such God-foresaken conditions!
 
The idea is to keep the mag’s impulse couplers from winding up and firing, which in some rare instances could cause an engine to “kick” or even start.

Caveats:

1) May not be great for the graphite vanes in a vacuum pump.

2) Must be avoided on ROTAX engines.

3) May not accomplish anything worthwhile.

The key should be to get the engine oil under pressure and flowing as soon as possible. The best way to accomplish this is to start the engine. Pulling the prop through in either direction may just be dragging unlubricated parts over each other with no documented benefit.

Historically, pulling the prop through on radial engines verified no hydraulic lock on the bottom cylinders, which could cause extensive damage if gone unnoticed. Very unlikely on our opposed-cylinder engines.

Or such is my understanding of current recommendations.
 
I am 100% convinced that turning the prop a few times prior to start in ice cold weather made starting my old C172 (O360) easier to start. On a trip from Florida to Arizona in the winter, with every morning below freezing, every start was an adventure that often wound up with the FBO bringing an APU around. On the next to last stop, some old guy at the FBO told us to turn the prop a few times before starting. We did and it started just fine. We did it again on our last stop before home and same good results. We did it again a few times before we sold it and we never again had a "cold start" problem. So I am convinced it helps.

But I was just wondering about the POH recommending turning the prop "opposite the direction of rotation". How important is that? And why?
 
I was taught (rightly or wrongly) that if for any reason I was manually moving the prop that is should ALWAYS be opposite direction for the same reason FastEddie8 has offered.

Even on my plane with no mags I follow that rule. It has dual electronic ignitions. It cannot start without the master and at least one ignition switch in the on position.
 
The idea is that by pulling the prop through, the oil is transferred from the bottom of the sump and into the pump to assist in lubricating the system. This helps relieve much of the tension that’s built up in the engine by the cold weather and will aid in start-up. I never do it, but that’s the basic idea.
 
FastEddieB said:
The idea is to keep the mag’s impulse couplers from winding up and firing, which in some rare instances could cause an engine to “kick” or even start.
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This

I right or wrong, I pull my prop through several time before most starts. Cold or warm.
 
I do pull the prop on my ROTAX through one revolution on every preflight.

The sole reason is to put each blade into reach for inspection.

Still curious about the physics that would cause oil to “limber up” with a few slow turns of the prop.
 
Ravioli said:
I was taught (rightly or wrongly) that if for any reason I was manually moving the prop that is should ALWAYS be opposite direction for the same reason FastEddie8 has offered.

Even on my plane with no mags I follow that rule. It has dual electronic ignitions. It cannot start without the master and at least one ignition switch in the on position.
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I pull mine through in the normal direction of rotation. However, I'm very experienced at propping planes and I treat the plane as though I'm trying to start it. When turning a prop, I always expect the plane to start and I'm prepared.

I know this isn't about propping a plane, but I've seen two near accidents when guys got tired from trying to start a plane and not having much luck. When they got tired, they made big mistakes. After a lot of pulls, one of the guys got it into his mind that it wasn't going to start ever. When it did, he almost stuck his hands in the prop. I convinced him to shut the plane down and skip the flight. He was too tired to make good decisions. The other one was where a plane wouldn't start and he pushed the throttle all the way forward and turned the prop backwards 8 times. This works when a plane is flooded. However, he forgot to pull the throttle back and when he propped it, it almost jumped the chocks. Luckily he had big rubber chocks like they use on 18-wheelers. Simply put, touch the prop, expect the plane to start.
 
FastEddieB said:
I do pull the prop on my ROTAX through one revolution on every preflight.

The sole reason is to put each blade into reach for inspection.

Still curious about the physics that would cause oil to “limber up” with a few slow turns of the prop.
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Isn't this a requirement on some Rotax engines? My friend flies gryos with 912s and 914s and he burps the engine. Something about a dry sump system...
 
I think F.E.B. has a good summary above.

Backwards pulling: I think I am the only one this has ever happened to (because whenever I mention it, the idea is promptly poo-pooed), but if you turn a dry vac pump backwards when the vanes are already pretty darned worn, you can break them. When I first bought my Viking, I had no idea of the vac pump hours. I turned the prop backwards to make room for the towbar. I heard a 'snick' or a 'tink'- the bad, unexpected kind of 'snick/tink'. I didn't really know what the sound was but the vac pump was on the list; I'd played with vanes & rotors before. Next start up; no vacuum. Opened the pump to find short, busted vanes. Probably a good way to learn that the pump needs o/h - on the ground rather than in the air, so I am not saying 'never turn the prop backwards'. So the risk to the dry vac pump is not an OWT, but it is exceedingly rare.

Way better than pulling the prop through is to run a cord to a simple box heater in the bottom cowl or incandescent light bulb in the exhaust stack.
 
Lowflynjack said:
Isn't this a requirement on some Rotax engines? My friend flies gryos with 912s and 914s and he burps the engine. Something about a dry sump system...
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The burping is solely to get oil from the sump into the oil tank in order to get an accurate and consistent measure of the oil level. Nothing else.

As an aside, I burp my engine and check the oils after each flight. Makes the burping much quicker and my plane lives in its own hangar, so it’s unlikely to be tampered with between flights.
 
steingar said:
Cold weather. Florida?


:p:p:p:):D:p:p:):):p:p:p:biggrin::lol::lol::lol::lol::D:D:p
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No. No cold weather here in Florida. That is why I am rather ignorant about it. But as I said, I am going to Ocoee TN next week and the temps will be in the low '20s. It might get down under 50 here, but that is a severe cold snap for us.
 
The quickest way I know to get oil circulating is to start the engine. Don't rev it. Keep it near idle till you see the gauge move.
 
Norman said:
The quickest way I know to get oil circulating is to start the engine. Don't rev it. Keep it near idle till you see the gauge move.
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The problem is that the thick, cold oil keeps the engine from starting.

It's kind of funny. Usually people say "do what the POH says", or "read your POH", but when I ask a question about what the POH says to do, people say "don't do that".
 
If you fly in winter very much you'll have days where you didn't have time to preheat as well as you'd like. On those days I pull my prop through in the normal rotation direction several blades to free up the stiff oil. It absolutely helps to save precious battery charge for a good initial start. If hand propping or cold key starting I'd use strokes of primer appropriate for the temperature and rotate the prop in the normal rotation direction several times to distribute the fuel ahead of starting.
 
Stewartb said:
On those days I pull my prop through in the normal rotation direction several blades to free up the stiff oil.
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Again, I’m unclear on the concept of how just moving oil around makes it less “stiff”.

Not saying it doesn’t, but seems like it would have to be heated to become less viscous
 
Stewartb said:
If you fly in winter very much you'll have days where you didn't have time to preheat as well as you'd like. On those days I pull my prop through in the normal rotation direction several blades to free up the stiff oil. It absolutely helps to save precious battery charge for a good initial start. If hand propping or cold key starting I'd use strokes of primer appropriate for the temperature and rotate the prop in the normal rotation direction several times to distribute the fuel ahead of starting.
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Would you do that even if the POH says "Always pull the propeller through by hand, opposite the direction of rotation. . ."?
 
FastEddieB said:
Again, I’m unclear on the concept of how just moving oil around makes it less “stiff”.

Not saying it doesn’t, but seems like it would have to be heated to become less viscous
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I obviously don't know, because I am the one asking the question, but my theory is that it doesn't make it less stiff, but it slowly puts a coating of oil on moving metal surfaces, making them easier for the starter to move.
 
JOhnH said:
The problem is that the thick, cold oil keeps the engine from starting...
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That's why many of us based in cold climates use multigrade.

I never pull the prop through on a cold engine as a matter of habit. I think it just scrapes the residual oil off the cylinder walls, and it does squat for "loosening up the cold crankcase oil".

If spark plugs, magnetos, battery and starter are maintained properly you should not have a problem starting it under reasonable ambient temp conditions. If your engine is not equipped with a Tanis or Reiff system, blanketing the cowl and using a electric cube heater will warm it up nicely in colder weather.
 
The stiff oil is in the cylinders and valve train. I spin 520 cubic inches with a little Odyssey battery.I'm very aware of the battery and starter's ability to crank my engine in different conditions. Rotating the prop helps when the engine is cold. When priming is involved I want the engine turning in the direction the induction is designed for. If I don't need start or priming assistance I don't turn the prop.

If you cold start your engine you'll probably notice the first blade or two are slow and then the starter picks up speed. I'd rather not force my small battery to deal with the initial blades being sticky slow since its so easy to deal with by hand.
 
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JOhnH said:
No. No cold weather here in Florida. That is why I am rather ignorant about it. But as I said, I am going to Ocoee TN next week and the temps will be in the low '20s. It might get down under 50 here, but that is a severe cold snap for us.
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I live up here in TN. In the summer I run 50 wt oil, come winter I change to 20/50 wt. When it is in the 20's my o-320 with 10:1's will have trouble starting if I don't preheat. I feel sure there may be increased wear also if not preheated but this is not the primary reason for preheating. My primary reason is I am not flying if I don't due to failure to get the engine started.
My preheater is simply a small electric box heater with a 6 inch to 4 inch heater duct reducer to the face and a 4 inch flex hose duct attached to the reducer. I tuck the flex hose in the bottom of the cowl.
 
If it got below freezing here more than once every few years, I might consider an engine heater, or even switching to multi-grade in the winter. But it doesn't, so I won't.
Besides, my POH, and my A&P recommend against multi-grade oil. I did switch to Multi-grade a few years ago when I was headed north for an extended trip in February. But I switched back when I got home (at the 25 hour mark).

In the meantime, I am just trying to do what the POH says, but I was wondering why it said that.
Perhaps, 50 years ago, when my POH was written, oils were different than they are now.
 
Um.... cold weather operation in FL. S9Somethingmething about that sentence got my head scratching

Sent from my SM-G935V using Tapatalk
 
JOhnH said:
No. No cold weather here in Florida. That is why I am rather ignorant about it. But as I said, I am going to Ocoee TN next week and the temps will be in the low '20s. It might get down under 50 here, but that is a severe cold snap for us.
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Where you flying into? I’m not too far from Ocoee.
 
I’m nearby as well.

Which airport? I think the only one near Ocoee is the Chilhowee Glider Port.

As an aside, over 60° around here today - quite unusual for December. But set to cool off a lot in a couple days.
 
Ryanb said:
Where you flying into? I’m not too far from Ocoee.
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FastEddieB said:
I’m nearby as well.

Which airport? I think the only one near Ocoee is the Chilhowee Glider Port.
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Cleveland (KRZR). (I don't have a glider)
I emailed them today asking about hangar space for a couple of nights, and a rental car.
 
Cool. I'm right up the road at Copperhill, TN.

Which has cheap fuel and might have a short-term hangar. Not sure about rental car availability, however.

Let me know if you have time to touch base regardless, or if I can help out in any way.
 
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Stewartb said:
If you fly in winter very much you'll have days where you didn't have time to preheat as well as you'd like. On those days I pull my prop through in the normal rotation direction several blades to free up the stiff oil. It absolutely helps to save precious battery charge for a good initial start. If hand propping or cold key starting I'd use strokes of primer appropriate for the temperature and rotate the prop in the normal rotation direction several times to distribute the fuel ahead of starting.
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I learned to fly in Alaska, and this is pretty much what I always did, including pre-priming and pulling the prop through. I don't know how effective propping is for freeing up the oil, but the pre-priming and propping does make a huge difference on starting when cold. If your battery is a little weak, you really want the engine to fire on the first 2 or 3 blades. I never propped an engine opposite of normal rotation... but as Jack mentioned, you should always treat a propped engine as if it will start on every pull, no matter what the configuration of the mag switches, throttle, etc.
 
...and which way you are turning the prop. Just a little kick back on compression may swing the prop enough to fire the mag.
 
FastEddieB said:
Cool. I'm right up the road at Copperhill, TN.

Which has cheap fuel and might have a short-term hangar. Not sure about rental car availability, however.

Let me know if you have time to touch base regardless, or if I can help out in any way.
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Thanks, I'd love to get together, but we are flying in Friday afternoon and having a rehearsal dinner that night. Then Saturday, I will have to spend time with a lot of relatives I haven't seen for years (some of that on purpose). Then the wedding and reception is Saturday afternoon and we fly out Sunday AM.

But I have always wanted to check out that area (as an adult) and plan to go back when we have more time. I used to go white water kayaking up there in the '70s. I know I haven't changed any, but I'm not sure about TN.
 
I can see the pre-priming and pulling through as helping. But it seems like it would do so by the fuel washing the oil from the cylinder walls. So while the engine might spin more freely, it would be at the expense of lubricating the rings for the short period until fresh oil is splashed on them. Not sure if that would make much of a difference if done rarely.
 
You warm climate guys just don't get it. If I go out and try to pull start a snowmobile or generator that's cold soaked the way I'll do it is to pull very slowly once or twice just to turn the motor over a time ir two, which reduces the subsequent pull effort greatly. It's common practice where its cold. But this thread isn't really about cold, just autumn cool. BIG difference.
 
Pulling the prop backwards prevents a hot mag from firing. If the POH told you to pull it through in the normal direction, and it fired and injured or killed you, the manufacturer woud get sued.

Pulling the prop backward does not get the oil pump moving oil into the mechanisms. It too turns backward when you pull backward, and actually moves oil OUT of the galleries and back into the sump.

If the vacuum pump broke while pulling backward, be grateful that it broke on the ground and not in IMC. Buy a pump with an inspection port (Rapco or Tempest) and follow the inspection instructions. You'll never bust a pump pulling backward that way.

Pulling through doesn't change the viscosity of the oil. It will make the engine easier to move, though, probably because the piston rings, which have considerable pressure on the cylinder walls, have had lots of time to penetrate the microscopic oil film and have firmly contacted the metal cylinder wall and are reluctant to go anywhere. Pulling the engine through re-smears oil over the walls and gets the rings unstuck. Oil is a lot stiffer in the cold, for sure, but there are other factors at work that we don't notice so much in warm weather. Cold batteries are far below their capacity; chemical reactions are slowed by cold, and that battery is just converting chemicals to other chemicals to make electricity. It can lose 80% of its cranking power in the cold. Stiff oil and parts stuck together just add to the agony.
 
I always check mag grounding as part of my shutoff routine. Doesn't mean something can't change between then and the next start, but it reduces the risk.

I pull thru when it's just parked and I'm fooling around in the hangar with no plan to fly. I used to do that with my stored cars...but too lazy now.
 
I think a poorly recognized aspect of the cold start problem is the need to get fuel into a cylinder in an ignitable form. This means the fuel-air mix has to be in a gaseous VAPOR form rather than just in a spray of liquid drops on a manifold or cylinder wall. Priming puts liquid fuel into a spray, but doesn't get it into a vapor - especially at cold temperatures. If there was a way to reduce the pressure below atmospheric, vapor formation would be much easier despite the cold temperatures. If the throttle is kept closed while the engine is cranking, the pressure in the intake manifold is considerably reduced, allowing any introduced prime to immediately flash into vapor and go on to the cylinder and hopefully ignition. However, as the throttle cracked open further the vacuum in the manifold quickly becomes less and less, and there is less incentive for the fuel to vaporize.

IOW - Save that last primer stroke for after the starter is spinning the engine.
 
Leaving the primer out and ready is SOP when cold starting. But there's a fine line between a successful start and frosted plugs. Proper preheat makes life much easier.
 
My opinion,, If it was cold enough to require you to pull it thru. Why didn't you pre-heat.??
 
My little airplane has no starter. I pull the prop through for one of three reasons: either I'm priming it, in which case I'm pulling the prop forward with the choke out (after running the electric fuel pump for a few seconds) to pull fuel into the cylinders. I'm starting it. Or, I've flooded it, in which case I'm pulling the prop through backwards with the fuel, mixture, master and mags off, and throttle full open, to clear the fuel out of the cylinders so I can start over.

The easiest way to get my little airplane started, even at 35 deg F (so far the coldest), is to stick a hairdryer on low in the bottom of the cowl with the cowl plugs left in for about 15 minutes. She starts right up on the 3rd of 4th blade. (before all the safety-nazis get started: I have no fuel leaks, I have a fire extinguisher, and I don't leave it unattended.)
 
Tom-D said:
My opinion,, If it was cold enough to require you to pull it thru. Why didn't you pre-heat.??
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Usually, you do. But if your battery is in the aft fuselage(typical) it is still at 15 below, or whatever. You really want the engine to catch on the first couple of blades. The procedure described makes a big difference.
 
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