Cold Starting Procedure and I'm an Idiot

[Stingray Don]

Welcome to this week's edition of Idiot's Anonymous. Hi, my name is Don, and I'm an idiot. There, I've said and I feel better.

I bought my 172N 2.5 years ago shortly after completing my PPL and it is the first and only plane I have flown with the manual primer. The POH just states, "Prime as required (2 to 6 strokes; none if engine is warm)". However, it has always been hard starting and nearly impossible during the cold weather. I recently stumbled on the fact that you have to wait at least 2-3 seconds for the fuel to fill the primer before pushing it back in. I had never heard that before and I've always just pumped the thing as quickly as I could and then started cranking (doh!). With the master on and the gyros spinning up, I couldn't hear the fuel flowing in the plunger. The last couple of flights I primed before turning the master on and I can hear how long it takes for the plunger to fill with fuel. Today with temps in the 30s, it started right up.

I guess this is just one of those common knowledge things that everyone assumes everyone else knows and nobody discusses. I hang my head in shame...

 

[coloradobluesky]

Pull it out slowly, it has to "fill up". Its like filling a syringe.

 

[RyanB]

And you'll notice it takes a little bit more force to push it back in once it's been pulled out for a couple of seconds. Using a pre-heater in the cold temps makes the engine even easier to start.

Don't let it get to ya, we've all had our stupid moments.

 

[Shawn]

...and not just wait three seconds...three seconds to slowly pull out to fill the primer, three seconds to push back in is what I do.

 

[Tom-D]

And remember that you don't push the primer in, until you are cranking the engine.

 

[GeorgeC]

The flip side is to wait a bit between priming and cranking to give the fuel a chance to evaporate.

 

[GeorgeC]

And remember that you don't push the primer in, until you are cranking the engine.

Ok, I'll bite. I thought if you had a primer, you primed, and if you didn't have a primer but had a carb with an accelerator pump, you pumped while cranking...

 

[Tom-D]

Ok, I'll bite. I thought if you had a primer, you primed, and if you didn't have a primer but had a carb with an accelerator pump, you pumped while cranking...

Ask your self, what carries fuel into the cylinders? why add fuel to the induction system if it is just going to drain down into the carb airbox? Add this thought, with out fuel in the induction system how can you have an induction fire.

try my method, you might like how fast the engine will start.

 

[SkyDog58]

And remember that you don't push the primer in, until you are cranking the engine.

Say what?!

 

[RyanB]

And remember that you don't push the primer in, until you are cranking the engine.

What? That's the first time I've heard of that.

 

[MAKG1]

Ok, I'll bite. I thought if you had a primer, you primed, and if you didn't have a primer but had a carb with an accelerator pump, you pumped while cranking...

You do what your POH says.

I don't think I've ever seen one that agrees with Tom's statement, but a 172 (prior to restart) POH agrees with you.

There are all kinds of wacky procedures. A 172RG explicitly tells you to pump the accelerator prior to cranking (even though it does have a primer). It's a sidedraft carb; it's not on the bottom of the engine, to make room for the nosegear retraction. The U206G I was just playing with a few days ago tells you to turn on the electric pump with the mixture already rich and push the throttle in.

 

[Tom-D]

Just because you've never heard of it, before doesn't make it wrong.
Remember the POH says " prime as required"
My method is a better method, pull the primer out, allow it to fill, turn the mags on, crack the throttle a wee bit, start cranking and pushing the primer in. the first cylinder to suck in fuel will fire and the engine will start and run.

 

[GeorgeC]

Ask your self, what carries fuel into the cylinders? why add fuel to the induction system if it is just going to drain down into the carb airbox? Add this thought, with out fuel in the induction system how can you have an induction fire.

I'm no A&P, but it was my understanding that the primer bypassed the induction system and squirted gas directly into the cylinder(s).

try my method, you might like how fast the engine will start.

That being said, I recently learned of using this method for cold weather starts and was planning on trying it soon.

 

[coloradobluesky]

No. It bypasses the carburetor and squirts it into the intake manifold. You can see the lines if you open the cowl and look at the engine.

 

[Tom-D]

I'm no A&P, but it was my understanding that the primer bypassed the induction system and squirted gas directly into the cylinder(s).



That being said, I recently learned of using this method for cold weather starts and was planning on trying it soon.

No primer system in GA places fuel in the combustion chamber. plus the statement that was made about using a side draft carb is simply wrong. all small Lycoming and Continental engines the start with an 0- ??? use the Marvel Schebler MA3 or MA4 carbs which are an up draft configuration.
When you pump the accelerator pump by cycling the throttle you simply throw fuel against the throttle plate in the carb, if there is no air traveling up the induction system that fuel simply falls down into the carb airbox then leaks out into the cowling.

 

[jordane93]

Pull it out slowly, it has to "fill up". Its like filling a syringe.

This.

 

[dmspilot]

It's better to pull slowly,
but is it better to push fast or slow?

 

[Tom-D]

No. It bypasses the carburetor and squirts it into the intake manifold. You can see the lines if you open the cowl and look at the engine.

Continental 0-200 primes the system at the remote mounted intake spider that allows all 4 cylinders to suck fuel from there. the 0-300-A-D primes the system by adding fuel to the left side "Y" pipe only 2,4,6 get primer fuel.
the Lycoming engines add fuel to only 3 cylinders they add this fuel at the intake port of the cylinder head outside of the intake valve.
In all cases you must crank the engine to get fuel into the cylinder's combustion chamber, simply because it is the air that is being drawn into the cylinder on the intake stroke that carries the fuel from the intake system to the combustion chamber.
Adding any fuel prior to cranking the engine simples fuel In the system with no ability to get it into the cylinder, so it simply drains down hill until it reaches the cowling.

 

[Tom-D]

You do what your POH says.

I don't think I've ever seen one that agrees with Tom's statement, but a 172 (prior to restart) POH agrees with you.

There are all kinds of wacky procedures. A 172RG explicitly tells you to pump the accelerator prior to cranking (even though it does have a primer). It's a sidedraft carb; it's not on the bottom of the engine, to make room for the nosegear retraction. The U206G I was just playing with a few days ago tells you to turn on the electric pump with the mixture already rich and push the throttle in.

I'll believe you were operating a fuel injected engine if you needed a electric pump. or maybe a PA-28 series low wing.

 

[brcase]

Induction fires are very rare.

It is very common to have fuel dripping from the engine compartment when priming. Cranking while priming will reduce/prevent this but may only work on some installations. But fuel dripping is so common that if this was a problem we would see a lot more fires than we do.

There usually isn't much of anything in a normal engine compartment that is going to start a fire. And there usually isn't much in the induction system that a fire will damage. Although I have seen some minor damage to an air filter.

I have over primed many times, the only two aircraft I ever had fires while starting, were actually both C-150's and both had mechanical issues. One had a bad mixture control and trying to start it in below 30degreeF conditions, It never would have started with the mixture problem but we didn't know that.

The 2nd aircraft would start an engine compartment fire almost every time we tried to start it below 30 degreesF, we would usually get it started ok. There really isn't much in the lower part of the engine compartment that will be damaged by fire. we reported it to maintenance every time, they kept checking it and couldn't find anything and of course once the engine started you couldn't replicate the fire, so it was hard to diagnose. About the 4th time it happened they finally disassembled the starter and found a rock inside the starter, they couldn't figure out how the rock got in there unless it was assembled with the rock in it. Only the last time did we ignite enough fuel to require a quick shot with the halon extinguisher. The only time I have to use a fire extinguisher around an airplane, btw Halon extinguishers work exceptionally well.
It never had a fire after that, even during cold weather starting.

However since then I have instigated a personal limit that it has to be unusual circumstances for me to try to start an aircraft engine below 30F without preheating it.

They just get too hard to start, and most people agree it is hard on the engine.

Brian
CFIIG/ASEL

 

[NKTFlyer]

This story was way better than I thought it would be. I watched a 150 literally drip fire a few weeks ago.

 

[Tom-D]

Induction fires are very rare.

It is very common to have fuel dripping from the engine compartment when priming. Cranking while priming will reduce/prevent this but may only work on some installations. But fuel dripping is so common that if this was a problem we would see a lot more fires than we do.

There usually isn't much of anything in a normal engine compartment that is going to start a fire. And there usually isn't much in the induction system that a fire will damage. Although I have seen some minor damage to an air filter.

I have over primed many times, the only two aircraft I ever had fires while starting, were actually both C-150's and both had mechanical issues. One had a bad mixture control and trying to start it in below 30degreeF conditions, It never would have started with the mixture problem but we didn't know that.

The 2nd aircraft would start an engine compartment fire almost every time we tried to start it below 30 degreesF, we would usually get it started ok. There really isn't much in the lower part of the engine compartment that will be damaged by fire. we reported it to maintenance every time, they kept checking it and couldn't find anything and of course once the engine started you couldn't replicate the fire, so it was hard to diagnose. About the 4th time it happened they finally disassembled the starter and found a rock inside the starter, they couldn't figure out how the rock got in there unless it was assembled with the rock in it. Only the last time did we ignite enough fuel to require a quick shot with the halon extinguisher. The only time I have to use a fire extinguisher around an airplane, btw Halon extinguishers work exceptionally well.
It never had a fire after that, even during cold weather starting.

However since then I have instigated a personal limit that it has to be unusual circumstances for me to try to start an aircraft engine below 30F without preheating it.

They just get too hard to start, and most people agree it is hard on the engine.

Brian
CFIIG/ASEL

Brian, YGTBSM. there are a multitude of ignition sources that can light off an engine compartment fire, bad mag lead. the mag points them selves, any loose wire that can arc, generator brushes, starter re-lays, battery master re-lays.

What gets destroyed in an induction fires? how about the red Scat hoses in the piper induction system, the filter, and when they're gone what stops the fire from spreading to the fuel in the cowl?

 

[MAKG1]

No primer system in GA places fuel in the combustion chamber. plus the statement that was made about using a side draft carb is simply wrong. all small Lycoming and Continental engines the start with an 0- ??? use the Marvel Schebler MA3 or MA4 carbs which are an up draft configuration.
When you pump the accelerator pump by cycling the throttle you simply throw fuel against the throttle plate in the carb, if there is no air traveling up the induction system that fuel simply falls down into the carb airbox then leaks out into the cowling.

Here is a link to a scanned and OCR'd POH for a 172RG. http://www.jasonblair.net/wp-content/uploads/2015/11/Cessna-172RG-POH-1980.pdf Page 7-22 describes the carburetor as a "horizontally mounted side draft" unit. Why should we believe you over this POH? It also identifies the engine as a Lycoming O-360-F1A6.

It also has an electric pump, but it's a Cessna with a carbureted engine. I suspect the reason is the location of the carburetor. Unlike the U206G, this one has a "both" position on the fuel selector.

 

[Lindberg]

Just because you've never heard of it, before doesn't make it wrong.
Remember the POH says " prime as required"
My method is a better method, pull the primer out, allow it to fill, turn the mags on, crack the throttle a wee bit, start cranking and pushing the primer in. the first cylinder to suck in fuel will fire and the engine will start and run.

I already need two hands and an elbow to hold the stick back, crack the throttle, and crank the engine. I'd need at least one more hand for your method.

 

[N747JB]

It's better to pull slowly,
but is it better to push fast or slow?

Ask her, they are all different!!

 

[Tom-D]

I already need two hands and an elbow to hold the stick back, crack the throttle, and crank the engine. I'd need at least one more hand for your method.

when you start at just above an idle, what will happen if you don't hold the stick back? do you have a weird beast that will nose over at idle?
once you crack the throttle isn't your hand free to do other things?

 

[James331]

Normally you can feel the difference between pushing a primer full of fuel vs air.

 

[RyanB]

I already need two hands and an elbow to hold the stick back, crack the throttle, and crank the engine. I'd need at least one more hand for your method.

What are you flying that requires that much aft force to hold the stick back??

 

[Tom-D]

Normally you can feel the difference between pushing a primer full of fuel vs air.

But you must experience both to know the difference.

 

[Tom-D]

Here is a link to a scanned and OCR'd POH for a 172RG. http://www.jasonblair.net/wp-content/uploads/2015/11/Cessna-172RG-POH-1980.pdf Page 7-22 describes the carburetor as a "horizontally mounted side draft" unit. Why should we believe you over this POH? It also identifies the engine as a Lycoming O-360-F1A6.

Just looked it up, the Parts catalog for 0-360 Lycoming series shows two different configurations of the oil sump used on the 0-360 one of which is a side draft that until now I never knew existed, And is noted in the application list is only found on a bastard child of Cessna C-177RG
But you still missed the point, neither carb is used in the primer system. which is just above the sump illustration at(http://rvplane.com/pdf/XP360_OverhaulManual.pdf) 6-4, fig 33 and shows a totally separate system that ports fuel to the intake port of the cylinder assembly just like all other configurations of the 0-360.
so, just the same, don't place fuel in a system that does not have airflow to carry the fuel into the cylinder.

 

[James331]

But you must experience both to know the difference.

If you're priming before each flight, think you would have noticed the difference, reminds me of people who do a mag check lightning fast, not even let each mag stabilize and sing its happy mag, or sad mag song, with corresponding CHTs/EGTs.

 

[Tom-D]

If you're priming before each flight, think you would have noticed the difference, reminds me of people who do a mag check lightning fast, not even let each mag stabilize and sing its happy mag, or sad mag song, with corresponding CHTs/EGTs.

now you invite thread creep

 

[slacktide]

No primer system in GA places fuel in the combustion chamber.

Only a Sith deals in absolutes. The Austro AE300 is diesel direct injection.

plus the statement that was made about using a side draft carb is simply wrong. all small Lycoming and Continental engines the start with an 0- ??? use the Marvel Schebler MA3 or MA4 carbs which are an up draft configuration.

Also incorrect. My airplane has an Lycoming O-360-A4K with a HA-6 side draft carburetor. Used in the Grumman Tiger and some Beech singles.

 

[Tom-D]

It also has an electric pump, but it's a Cessna with a carbureted engine. I suspect the reason is the location of the carburetor. Unlike the U206G, this one has a "both" position on the fuel selector.

No I just looked up the side draft carb you have is a Bendix pressure carb. it works on a different principal that the Marvel Shebler that real aircraft have
correct that, Marvel is now making them, and have renamed them the HA-

 

[Tom-D]

Also incorrect. My airplane has an Lycoming O-360-A4K with a HA-6 side draft carburetor. Used in the Grumman Tiger and some Beech singles.

see post 31. add your's to the list.

 

[slacktide]

The Lycoming engines add fuel to only 3 cylinders

Also incorrect. Refer to figure 34 in the O-360-A parts catalog. The number of primer lines is dependent on the engine model, and there are several models that prime all 4 cylinders.

 

[Mtns2Skies]

I agree with @Tom-D . I give the last shot of prime while I'm cranking the engine and I notice it starts WAY better(3 hands required ) Particularly in cold weather. One CFI showed me this and explained it's because the primer aerosolizes the fuel. If you wait too long it re-liquifies and is harder to start..

 

[Tom-D]

I agree with @Tom-D . I give the last shot of prime while I'm cranking the engine and I notice it starts WAY better(3 hands required ) Particularly in cold weather. One CFI showed me this and explained it's because the primer aerosolizes the fuel. If you wait too long it re-liquifies and is harder to start. because the fuel is now in the cowl. .

FTFY.

 

[Tom-D]

Only a Sith deals in absolutes. The Austro AE300 is diesel direct injection..

then it won't need a primer system.

 

[Tom-D]

Also incorrect. Refer to figure 34 in the O-360-A parts catalog. The number of primer lines is dependent on the engine model, and there are several models that prime all 4 cylinders.

Post #1 we were talking about a 0-320-
some do some don't 0-320 just 2 unless added to the system as an after thought.