When to Hot Start

[MBDiagMan]

I have rarely had difficult with hot start procedures on my IO360 as long as I know that it’s hot.

Today it was probably in the sixties and I flew to a nearby airport, took a courtesy car and went to a funeral service.   Got back in the plane almost exactly two hours and ten additional degrees ambient later.  After turning on the master I checked cylinder temps on the JPI.  Two were 100 and the other two were 102.  From that I figured it would light right off using cold start procedures but I was wrong.  I, of course, got it flooded.  Once I let it set a minute or so, I switched flooded start procedures and got it started without much trouble.

So……… what constitutes the need for cold start procedures and what constitutes the need for hot start procedures?

[carusoam]

The amount of prime used for a warm start is very different than a cold start…

In this case…

Prime enough to have the FF gauge show movement… a second or two…

It is all about how easily 100LL evaporates…

Hot starts are extra different because the hot fuel lines have fuel boiling in them… causing extra fuel to be delivered unexpectedly…

 

How does that sound?

IO550 experience only… No IO360 experience to draw from…

Best regards,

-a-

[MBDiagMan]

That might be the key.  For a cold start I run the fuel pump long enough to see normal fuel pressure on the JPI.  Maybe a short burst, or no burst is the key for a partially warm engine.

[carusoam]

Where some confusion occurs…

When we shut down using the mixture knob… we drain the fuel lines a distance back in the fuel injector system…

Fill it back up… but don’t fill it an push extra into the engine…

The extra is what is too happy to evaporate in a warm engine…

My engine doesn’t have a fuelP sensor, unfortunately…  FF only…

 

More PP thoughts only,

-a-

[EricJ]

I'll do "warm start" as well, which is just anywhere from one to three seconds of prime depending on how long it's been sitting.  So far I've had good luck that way.

 

[eman1200]

I don’t have all that fancy engine gadgetry u got but after sitting for two hours I also would have considered a cold start, especially since u only took a local flight. However, oddly enough, I took a local flight today, sat for almost 2 hours and did a mighty fine hot start, if I do say so myself.

[ShuRugal]

I use the same start procedure, regardless of how "cold" or "hot" the engine is. The only thing I change is how many pumps I give the throttle to prime it.

Mixture rich
Boost pump to 6 psi
Prime with throttle, 0 to 5 strokes
Mixture to cutoff
Throttle to idle position
Crank
Advance mixture after the engine fires
Adjust mixture for stable idle

The thing to keep in mind is that the engine will always fire if it has a combustible mixture. It's hard to control exactly how much fuel is in, and it's easy to make it too rich.

By always cranking with the mixture at cutoff after doing some amount of priming, you guarantee that the mixture will fall through the combustible range and fire, at which point you now know what the mixture is and can add fuel to control it.

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[A64Pilot]

Pumping the throttle doesn’t do anything on an IO does it?  I know some carbs have accelerator pumps and on them pumping is of course effective.

[carusoam]

Position of the throttle may change the FF / Time required to prime… (it does for the IO550)

Pumping without an accelerator pump won’t….

-a-

[ShuRugal]

Pumping the throttle doesn’t do anything on an IO does it?  I know some carbs have accelerator pumps and on them pumping is of course effective.

That's a good point. I was thinking on terms of carburetor.

With an injected engine, I would instead just run the boost pump with the mixture and throttle both fully forward for a couple seconds until pressure rises, then pull everything back to idle/cut and crank

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[RLCarter]

On my E, I could cold start at my hangar, taxi to the fuel pumps which was maybe 3~5 minutes run time, that was enough to have to use the Hot Start method. Never had an issue after it sat more than an hour regardless of ambient temp

[A64Pilot]

An IO Lycoming will boil the fuel out of its injector lines and maybe the spider after shutdown, so warm or cold start your injection lines are full of air.

The difference between hot or cold start is the amount of prime needed, normal hot start is to flood the engine slightly, but start with throttle wide open allowing the most air in, and mixture off, this obviously pretty quickly unfloods  the engine and as it starts you of course reduce throttle and add mixture.

The hot start procedure will work on either a hot or cold engine, it’s just easier on a cold engine to know how much you primed, but a hot motor may still boil the fuel or not, so you start with a flooded motor whether you need it or not.

As I understand it the difference between a Conti and a Lyc is two fold, first Conti runs the lines underneath and therefore out of the hottest area, and secondly I believe it’s possible to pump fuel through the Conti system without flooding the engine and clear the vapor lock, done correctly there really is no need for a hot start like a Lyc where you flood the engine.

 For me if my Lyc is having a hard time during a hot start it’s always been plugs that needed cleaning, if you have a weak ignition system it really shows up then

Edited April 3, 2022 by A64Pilot

[A64Pilot]

35 minutes ago, ShuRugal said:

That's a good point. I was thinking on terms of carburetor.

With an injected engine, I would instead just run the boost pump with the mixture and throttle both fully forward for a couple seconds until pressure rises, then pull everything back to idle/cut and crank

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I have a neighbor that pumps his throttle on his Bonanza when she stumbles after a start even though I’ve shown him low boost is more effective

[ShuRugal]

I have a neighbor that pumps his throttle on his Bonanza when she stumbles after a start even though I’ve shown him low boost is more effective

I watched a DA 40 do this at SFQ today. Cranked for about 15 seconds, stopped and fiddled with levers energetically enough that I could see him jiggling, cranked for another 15, spluttered to life in a plume of black smoke, then powered up so fast he squatted the nose gear.

Then I started as described above: mixture rich, boost to 6 PSI, idle cut, crank. It fired on the third blade, I released the key, advanced the mixture, and was idling at 1,100.

We were both in SFQ for the same amount of time, he arrived only moments after I did.

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[M20F]

The key is whenever In doubt, just flood it and then there can be no doubt. 

[MikeOH]

Unless it’s a true cold start(like 5 hours) I use the Don Maxwell hot start procedure: leave the throttle where it was at shutdown (around 1000rpm) , mixture at ICO, crank and slowly advance mixture.

I also find opening the oil door is a great way to vent heat if I’m only gone for an hour, or so .

[RLCarter]

3 minutes ago, M20F said:

The key is whenever In doubt, just flood it and then there can be no doubt. 

The problem with that is your chance of an induction fire goes way up….. just remember to just keep cranking if a fire occurs and it doesn’t start…

[A64Pilot]

50 minutes ago, RLCarter said:

The problem with that is your chance of an induction fire goes way up….. just remember to just keep cranking if a fire occurs and it doesn’t start…

Not too many years ago a Maule was burnt to the ground at Jack Brown’s seaplane base, instructor was showing if your not sure, flood it good then you know, but it caught fire and burned.

IO engines are not the best for float planes as they often push off then get carried down stream.

[Hank]

1 hour ago, ShuRugal said:

I watched a DA 40 do this at SFQ today. Cranked for about 15 seconds, stopped and fiddled with levers energetically enough that I could see him jiggling, cranked for another 15, spluttered to life in a plume of black smoke, then powered up so fast he squatted the nose gear.

Then I started as described above: mixture rich, boost to 6 PSI, idle cut, crank. It fired on the third blade, I released the key, advanced the mixture, and was idling at 1,100.

We were both in SFQ for the same amount of time, he arrived only moments after I did.

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Just another reason to love our Cs! Hot starts are simple. 

But this thread is about hot starting the IO-360 found in E, F and J models. As I understand it, there are several hundred sworn methods used by several hundred pilots & owners. We  however, have one fine method that works well!

[MBDiagMan]

Yep, I wish I had never hurt my shoulder causing me to have to get rid of my C.

[Ragsf15e]

15 hours ago, MBDiagMan said:

I have rarely had difficult with hot start procedures on my IO360 as long as I know that it’s hot.

Today it was probably in the sixties and I flew to a nearby airport, took a courtesy car and went to a funeral service.   Got back in the plane almost exactly two hours and ten additional degrees ambient later.  After turning on the master I checked cylinder temps on the JPI.  Two were 100 and the other two were 102.  From that I figured it would light right off using cold start procedures but I was wrong.  I, of course, got it flooded.  Once I let it set a minute or so, I switched flooded start procedures and got it started without much trouble.

So……… what constitutes the need for cold start procedures and what constitutes the need for hot start procedures?

If any doubt, use hot start technique of not touching anything after shutdown, just cranking and increasing mixture when it fires.  Always try this first on the 2nd flight of the day. 95% it works.

If it doesn’t, and it’s been a few hours and likely cool, short prime, normal start.

If those don’t work or it’s hot and you missed the start, use flooded.

Follow that decision tree and you’ll be in great shape.

[PT20J]

1 hour ago, Ragsf15e said:

If any doubt, use hot start technique of not touching anything after shutdown, just cranking and increasing mixture when it fires.  Always try this first on the 2nd flight of the day. 95% it works.

If it doesn’t, and it’s been a few hours and likely cool, short prime, normal start.

If those don’t work or it’s hot and you missed the start, use flooded.

Follow that decision tree and you’ll be in great shape.

Exactly.

The problem with starting (hot or cold) is that liquid gasoline will not combust, and a mixture of gasoline vapor and air will only combust over a narrow ratio of fuel to air. It is easy to get confused about whether the engine needs more or less fuel when it won't start. Using Drew's procedure methodically gets you to a known mixture state first assuming that the mixture is too lean and ending up knowing that it is too rich. 

When you shut down the engine, the RSA flow divider has a valve that cuts off fuel to the injectors for a clean shutdown. Heat will boil off this trapped fuel. This is why Don's hot start procedure works. As the engine is cranked, he slowly advances the mixture control which introduces fuel until a combustible mixture is reached. Although it is not necessary to use the boost pump for starting (except for priming before starting) it will not flood the engine if the mixture is in idle cutoff. The main reason for not using the boost pump is that if the engine does not start and you quit cranking and leave the mixture off idle cutoff you will quickly flood the engine. 

When priming a cold engine the throttle should be opened at least 1/4 travel. The RSA servo does not have enough airflow at low engine speeds to accurately meter fuel and has a mechanical idle circuit that restricts fuel flow at low throttle settings. This throttle/idle mixture connection what you are adjusting when you turn the idle mixture thumbscrew. If you don't have the throttle open enough it will effect the prime fuel flow and make it difficult to get a consistent amount of prime.

The RSA injectors are small orifices that restrict the fuel flow -- they do not atomize the fuel. So on a cold start, it may be beneficial to wait a up to 30 seconds after priming to allow the prime fuel to begin evaporation. Remember that liquid fuel will not combust. With a warm or hot engine, the fuel will evaporate quickly when it hits the metal components in the cylinder head and waiting is not beneficial as the prime fuel will boil off and the mixture may be too lean to start, or more likely, there won't be enough prime fuel to keep it running.

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[Fly Boomer]

I think it was Mike Busch who said "if it's summer, you probably over-primed; if it's winter, you probably under-primed".

[M20F]

On 4/2/2022 at 8:49 PM, RLCarter said:

The problem with that is your chance of an induction fire goes way up….. just remember to just keep cranking if a fire occurs and it doesn’t start…

Not an issue on the IO360 which was the question. 

[RLCarter]

1 hour ago, M20F said:

Not an issue on the IO360 which was the question. 

And why won’t an IO360 catch fire if flooded? They puke fuel like all the rest