Cold Starting

Jeanie

Jeanie

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Jeanie
I have been told that on cold mornings you should pull the prop thru a few times to distribute the oil but then I was told that 'no' that would make the rings clear the oil off the inside of the cylinders and would be worse...

Can an A/P please explain this to me :rolleyes:

the engine is a Lycoming O-235 L2C
 
Jeanie said:
I have been told that on cold mornings you should pull the prop thru a few times to distribute the oil but then I was told that 'no' that would make the rings clear the oil off the inside of the cylinders and would be worse...

Can an A/P please explain this to me :rolleyes:

the engine is a Lycoming O-235 L2C
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Jeanie,

Not an A&P, but FWIW: There are more Old Wives Tales about how to start a cold engine than I can count. Every cold start does damage to your engine in a small way. The various OWTs just focus on not damaging the part du jour and ignore the other damage elsewhere.

Clearly the best advice is a thorough preheat. There is no substitute. That may include Reiff and Tanis systems, too, as a thorough preheat.

The OWT about pulling the prop through to distribute the oil, or to "limber up" the oil, is in this category. Does it really? It is the high wing or low wing debate! Each has its core of believers. Pulling through does ignore what may be happening to the cylinder walls. And how bad is it for the cylinder walls? Any observable damage? I don't know.

So sit back, get the popcorn at the ready. There should be a host of opinions posted shortly.

-Skip
 
So sit back, get the popcorn at the ready. There should be a host of opinions posted shortly.

-Skip[/quote]

~~~~~~~~~~~ That's one of the reasons I love this forum. Folks post their thoughts and opinions and you can learn alot from it.

I guess the other question is what is "cold"... I live in Alpine, TX and frankly for me if it's below 70 degrees I'm cold :yesnod: but for the purpose of the engine what's cold??? 40 degrees? 30 degrees? when does oil become too viscous to flow easily on start -
 
My POH recommends pulling the prop through. Besides, if it is cold, you can shoot a two or three shots of prime, pull the prop through 15-20 times, and the engine will fire right up. Just keep the throttle low.
 
I have encountered the situation that the starter won't be able to pull the engine through unless you give it a couple of blades by hand beforehand. May just have been weak connections or battery, but that plane definitely benefited from being pulled through when cold (10f cold).
 
After three blades (make SURE fuel is off, mags grounded and your P-leads work), start it with the Carb heat ON. It just increases the length of the draught tube, lowering MP and enrichening the mixture slightly (old Int'l Falls MN trick).
 
How cold does it get where you are in TX? "Cold" covers a lot of ground, and what to do is related to exactly how cold cold is...


Trapper John
 
My C-172 is too cold to start by itself at 20*F. Warmer than that, it starts OK. To warm the engine takes at least 30 - 60 minutes in the hangar or with the heavy-duty heater at the airport if the hangar is full.
 
Let's just say between 30 and 40 *F. is what I'm using as "cold" - frankly, if it's colder than that I'm inside.
 
bbchien said:
After three blades (make SURE fuel is off, mags grounded and your P-leads work), start it with the Carb heat ON. It just increases the length of the draught tube, lowering MP and enrichening the mixture slightly (old Int'l Falls MN trick).
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I hadn't heard that one before. I wonder if the real benefit is bypassing a frosted-over air filter.


Trapper John
 
Jeanie said:
staright weight. Aeroshell 100 SAE 50
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Straight 50 weight usually has a minimum recommended air temperature of about 60 F. Might want to look at 15W-50 multi-vis, but double check your engine documentation to see what is acceptable.


Trapper John
 
Trapper John said:
Straight 50 weight usually has a minimum recommended air temperature of about 60 F. Might want to look at 15W-50 multi-vis, but double check your engine documentation to see what is acceptable.


Trapper John
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To John's point, here is a website with more oil information than you can shake a stick at. While not aviation specific, it's good info.

http://www.bobistheoilguy.com/

Click "viscosity charts" on the left hand column.
 
Here my advice...start it and actually keep your rpm 800-1200..for about 3-5 mins ..let the thing warm up before run-up power and takeoff...IMO thats where the damage takes place.
 
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bbchien said:
After three blades (make SURE fuel is off, mags grounded and your P-leads work), start it with the Carb heat ON. It just increases the length of the draught tube, lowering MP and enrichening the mixture slightly (old Int'l Falls MN trick).
Click to expand...


That can start an induction fire if there's a small exhaust leak. If the engine backfires through the carb, which is common enough when it's cold and the mixture is a hair too lean to start right up, puddled fuel can be blown out of the intake and into the heat muff around the exhaust.

I prefer to pull the carb heat as soon as the engine has started. The heat helps the fuel spray to vaporize in the intake manifold and gets things running smoother.

We start our fleet at temps down to about -10°C (14°F or so) and we're using Aeroshell 15W50. RPM is set to between 800 and 1000. Too slow and no oil is thrown into the cylinders. Too fast and the pump might cavitate in that thickened oil and pump nothing. Getting the prime exactly right is the biggest hassle; the plugs are cold and can get frosted and shorted out after the first few firings if the engine doesn't keep running. Priming and then fooling around too long before starting just results in the fuel settling out of its atomized state and running down the induction piping. Too much prime lets fuel run back through the carb and presents a risk of fire, and fllods the engine; too little and you'll kill the battery. Since the battery loses about 80% of its capacity at 0°F, it'll die quickly and if left out in the cold in a discharged state, it could freeze and split.

But preheating, or hangaring in a heated place, is surely the best thing. Starting a really cold engine is a good way to be forced out of flying altogether. The repairs will either get hugely expensive, or it might come apart in flight due to damage suffered during startup. A heated hangar also reduces the frequency of gyro replacement, since the bearings in those things run in a fine grease that freezes in the cold and is forced out so they run dry for awhile after startup.



Dan
 
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Good advice, Dan -- thanks!!

My Lycoming O-145 Operators manual suggests that "Engine is warm enough for takeoff when the throttle can be opened without back-firing or skipping of the engine."

I start at throttle cracked which is about 600 RPM. Once I can reach the throttle I push it up a bit until it reaches 800 RPM. It will advance to 1000 RPM as it warms.

I'm running Phillips XC 15-50, and so far oil consumption less than 1/2 quart per ten hours (once it blows anything over 3.5 quarts out). I was going to switch to AeroShell but why mess with success?
 
Dan Thomas said:
. A heated hangar also reduces the frequency of gyro replacement, since the bearings in those things run in a fine grease that freezes in the cold and is forced out so they run dry for awhile after startup.Dan
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A ceramic heater placed in the cabin is another option here..makes a big difference
 
Jeanie said:
Let's just say between 30 and 40 *F. is what I'm using as "cold" - frankly, if it's colder than that I'm inside.
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That's not cold. :no: Or, at least, it's not the kind of cold that most people seem to be talking about in this thread!

Below 40F, we start plugging the engine heaters in, but that's it.
 
While many POH's of planes with Lycoming engines say to pull the prop through, Lycoming agrees with Jeanie's mechanic. Numerous Lycoming pubs say don't pull their engines through for cold starts -- it doesn't have any positive benefit, and it can abrade piston rings and cylinder walls. I choose to believe Lycoming over the airframe manufacturer in this regard. The only exception is radial engines (which Lyc hasn't built in a while) because you have to check for hydraulic lock on the bottom cylinders.

Once started, Lycoming recommends keeping the engine in the 1000-1200 RPM range until the oil starts to warm up. You'll know this when the engine runs smoothly at idle, the oil temp comes up off the peg, and the oil pressure peaks and starts down. It's best to wait until the oil temp reaches the green arc before run-up, but if the engine accelerates smoothly to run-up RPM, they say you can safely run the engine up without regard to the green arc.

As always, a thorough preheat is your best friend for both a good start and maximum engine longevity and reliability.

As for oil, if you use single-weight oil, note the ambient temp limit for the various grades. You don't want to be using SAE 50 oil in winter weather. Either use multigrade year-round (I use Exxon Elite 20W50) or change to SAE 40 when the weather starts to get cold (or even lighter oil, like Aeroshell 65, in really cold places). BTW, one reason I use multigrade year-round is from time to time, I make north/south trips where one night it's 25F and two days later it's 85F.
 
Well, my plane did backfire the other day when I started it and I was first worried about fire - there wasn't one and then whether I should shut down and pull the cowl and look for damage. Not sure what I would be looking for exactly but I worried about it briefly... then let it warm up, taxi'd around some, did the run up and everything sounded and did right so I flew it.

Should I pull the cowl and look for damage... ? Guess I'll change the oil to multi weight or lower weight till spring and warmer temps get here... spose I could keep the drained oil for future use since it's not old? I hate to just toss it.
 
I would hate to waste the oil too, but I'd toss it. It's be a pain to keep around in a clean fashion. The way I spill oil, I'd rather spill clean oil into the cowl. :)
 
Jeanie said:
Guess I'll change the oil to multi weight or lower weight till spring and warmer temps get here... spose I could keep the drained oil for future use since it's not old? I hate to just toss it.
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I knew a guy who drained his oil after every flight - He didn't have a preheater, so he'd drain the warm oil. He made an insulated box in his hangar where he'd store the oil in bottles, and he would come by every day and put a fresh set of hot water bottles in there as well to keep the oil warm. When he wanted to go flying, he'd pour the warm oil into the engine and go... :yes:
 
flyingcheesehead said:
I knew a guy who drained his oil after every flight - He didn't have a preheater, so he'd drain the warm oil. He made an insulated box in his hangar where he'd store the oil in bottles, and he would come by every day and put a fresh set of hot water bottles in there as well to keep the oil warm. When he wanted to go flying, he'd pour the warm oil into the engine and go... :yes:
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~~~~~~~~ Oh my gracious ! Well, you are in Wisconsin afterall and it gets quite cold up there
 
flyingcheesehead said:
I knew a guy who drained his oil after every flight - He didn't have a preheater, so he'd drain the warm oil. He made an insulated box in his hangar where he'd store the oil in bottles, and he would come by every day and put a fresh set of hot water bottles in there as well to keep the oil warm. When he wanted to go flying, he'd pour the warm oil into the engine and go... :yes:
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Did he log it in the maintenance log???? :rolleyes:
 
flyingcheesehead said:
I knew a guy who drained his oil after every flight - He didn't have a preheater, so he'd drain the warm oil. He made an insulated box in his hangar where he'd store the oil in bottles, and he would come by every day and put a fresh set of hot water bottles in there as well to keep the oil warm. When he wanted to go flying, he'd pour the warm oil into the engine and go... :yes:
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Read that in some old-fashioned bush-flying stories. If you have to stop for the night during the winter, you drain the oil into a little jerry can, wrap it in a blanket, stick that into your sleeping bag to keep you warm for the night. In the morning, you heat the oil-can over the campfire, pour it in the engine, fire up an go.
 
Jeanie said:
Guess I'll change the oil to multi weight or lower weight till spring and warmer temps get here... spose I could keep the drained oil for future use since it's not old? I hate to just toss it.
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Use it in your car.
 
Jeanie, another data point:
I use Phillips XC 20W50 year round in my IO520 and preheat when it is supposed to be below ~40F, using one ordinary 12" box fan/heater on medium, placed below the engine aimed upwards. Usually brings temps up to 70F per JPI readings.
Occasionally I will have to start up in minus C temps (after a day skiing at angel fire) but I don't worry about it that much.
No 'oil limbering' (prop exercising) here.

PS the 'backfiring' is most likely a result of a too rich start. High altitude often results in over-rich mixtures. I have experienced it several times and it goes away if I do not prime quite so much. Yes it can damage components and warrants a look-see. Any explosion outside the combustion chamber can be bad.
 
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Most GA engines will start up no problems at those temps. As far as the internal damage from a cold start, who knows? Logically, it seems to make sense that a cold start would cause problems. That said, I've never heard of anyone trashing their engine from a cold start...

As a realworld example, the Lyc O-360-A4A in my Cherokee does perfect @ 40. turns over albeit a bit sluggish @ 30, and struggles to fire @ 25degF. Getting it to start @ 20deg without a preheat would be difficult.

I think that the cold-soaked battery is also part of this problem, as it is less capable of delivering current.


Jeanie said:
Let's just say between 30 and 40 *F. is what I'm using as "cold" - frankly, if it's colder than that I'm inside.
Click to expand...
 
Ron Levy said:
While many POH's of planes with Lycoming engines say to pull the prop through, Lycoming agrees with Jeanie's mechanic. Numerous Lycoming pubs say don't pull their engines through for cold starts -- it doesn't have any positive benefit, and it can abrade piston rings and cylinder walls. I choose to believe Lycoming over the airframe manufacturer in this regard. The only exception is radial engines (which Lyc hasn't built in a while) because you have to check for hydraulic lock on the bottom cylinders.
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I strongly suspect that the OWT about pulling the prop through came from the need to do that on radials to prevent hyrdo lock issues. I also believe (and have confirmed for myself on a few engines) that moving the prop by hand does not measurably decrease the force required to crank the engine. If you try this some time (only on an engine with tested mag switches in the off position and no fuel in the engine) try to get a feel for the force necessary between the first couple compression strokes compared with the last couple and I think you'll find the force isn't diminished at all. It is plausible that by "scraping" the oil off the cylinder walls you increase the ring leakage enough to lower the compression hump which could indeed allow a weak battery to crank the engine better but I've not experienced that either. There is also some chance that by turning the prop you will cause the crankshaft throws to displace some congealed oil from their path through the crankcase but that would only occur when the oil is so cold it's more like grease and you really shouldn't be starting an engine with oil in that state as it's quite possible to cavitate the oil pump and ruin the engine. Most likely the only advantage of moving the prop by hand before starting is simply the result of positioning it to a point where the next cylinder to fire is far enough up the compression stroke that the starter can get the engine rotating fast enough for inertia to help get past the next compression.

Once started, Lycoming recommends keeping the engine in the 1000-1200 RPM range until the oil starts to warm up. You'll know this when the engine runs smoothly at idle, the oil temp comes up off the peg, and the oil pressure peaks and starts down. It's best to wait until the oil temp reaches the green arc before run-up, but if the engine accelerates smoothly to run-up RPM, they say you can safely run the engine up without regard to the green arc.
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I think the main issue for delaying the runnup is preventing excessive oil pressures. With straight summer weight oil the pressure regulating bypass and oil filter bypass often cannot pass enough oil (grease really) to limit pressures to tolerable levels if the RPM is very high. For the most part, cold oil that's flowing well will lubricate just fine, the exception being the decreased splashing of oil onto the cylinder walls.


As always, a thorough preheat is your best friend for both a good start and maximum engine longevity and reliability.

As for oil, if you use single-weight oil, note the ambient temp limit for the various grades. You don't want to be using SAE 50 oil in winter weather. Either use multigrade year-round (I use Exxon Elite 20W50) or change to SAE 40 when the weather starts to get cold (or even lighter oil, like Aeroshell 65, in really cold places). BTW, one reason I use multigrade year-round is from time to time, I make north/south trips where one night it's 25F and two days later it's 85F.
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Multigrade is the only way to go if you fly between climate extremes. AFaIK the only downside of mult-vis oil is the increased susceptibility to molecular shearing (the oil molecules get broken into smaller HC chains) which decreases the viscosity at higher temps. There is a downside to using thinner oil in the winter as well, once the engine and oil reach normal operating temps, the thinner oil doesn't protect the bearings as well.
 
gismo said:
I think the main issue for delaying the runnup is preventing excessive oil pressures. With straight summer weight oil the pressure regulating bypass and oil filter bypass often cannot pass enough oil (grease really) to limit pressures to tolerable levels if the RPM is very high. For the most part, cold oil that's flowing well will lubricate just fine, the exception being the decreased splashing of oil onto the cylinder walls.
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Cold oil can, for sure, make the pressure too high. Oil coolers have been known to split this way. But the larger issue is the reluctance of the oil in the sump or tank to be sucked into the pump in the first place. You know those really thick milkshakes that are easier to eat with a spoon because you can hardly get it up the straw? That's the way it is with cold oil too. Put a quart of 80 or 100 in your deepfreeze overnight, and see how easily it pours when you take it out. And the deepfreeze doesn't get nearly as cold as the weather around here. If the pump can't get the oil, nothing gets the oil.

Dan
 
gismo said:
There is a downside to using thinner oil in the winter as well, once the engine and oil reach normal operating temps, the thinner oil doesn't protect the bearings as well.
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Some engines never reach those temps in cold air, so I can only guess (no evidence) that the lower viscosity of a multiweight helps when you're pushing oil at less than optimal oil temp.
 
Dan Thomas said:
Cold oil can, for sure, make the pressure too high. Oil coolers have been known to split this way. But the larger issue is the reluctance of the oil in the sump or tank to be sucked into the pump in the first place. You know those really thick milkshakes that are easier to eat with a spoon because you can hardly get it up the straw? That's the way it is with cold oil too. Put a quart of 80 or 100 in your deepfreeze overnight, and see how easily it pours when you take it out. And the deepfreeze doesn't get nearly as cold as the weather around here. If the pump can't get the oil, nothing gets the oil.

Dan
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It's certainly true that iif the oil in the sump is fully congealed the pump will cavitate (I mentioned that in the first paragraph of the post you quoted) but you might be surprised how thick the oil can be and still flow to/through the pump. The limiting factor on that is whether or not the 14+PSI ambient pressure can push the goo up the pump inlet and if that happens it doesn't much matter what the RPM is. In any case it's definitely possible to build enough pressure to rupture an oil filter or cooler if you rev up when the oil is barely "thin" enough to make it to the pump.
 
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