How long for a hot start

[gwav8or]

So I got my first experience with “hot start” yesterday. Temps were in the low 90s. CFI and I flew about an hour, stoped at a local airport to grab some lunch. Plane had sat for a little over an hour. After a few attempts we used Don Maxwells procedure and got it started.

 

That has me wondering. What’s the approximate time range for how long a hot start will be needed? Obviously OAT will play a factor. Seemed to me it should have cooled enough in an hour to not need hot start procedures. But this is my first fuel injected engine and I’m just trying to learn.

 

Thanks!

 

 

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[carusoam]

Much of the hot start waiting time…

Has to do with the…

• Machine
• pilot
• weather conditions

Some engines…

When you hear the fuel boiling under the cowl…. You know the hot start technique is going to be required… this may be going on for a few minutes after landing….

So…. It is often a challenge during fuel stops on long X-countries…

 

Often, an hour after shut down… a warm start works…

 

Getting used to how your engine works makes it easy…

When to use the fuel pump… when not to…

How much fuel is needed to refill the fuel lines after shut-down…

The IO550 makes it a bit easier because you can run cold fuel through the system and send the warm stuff back to the tank it came from (in some cases)… 

Best regards,

-a-

[PeteMc]

18 minutes ago, gwav8or said:

Don Maxwells procedure and got it started.

What is Don's procedure?  I have a friend with an F (Trophy mods) and often has hot start issues.  Mechanic has given him a procedure (which I don't remember exactly) and it seems to work.  Curious what he'll say on the comparison with Don's.

 

[carusoam]

14 minutes ago, PeteMc said:

What is Don's procedure?  I have a friend with an F (Trophy mods) and often has hot start issues.  Mechanic has given him a procedure (which I don't remember exactly) and it seems to work.  Curious what he'll say on the comparison with Don's.

 

Don has a video posted around here…

Essentially begin the start process with the mixture pulled… advancing slowly until the mixture is right… continue advancing as needed…

Find Don’s video it is short, sweet, and memorable…

Best regards,

-a-

[ArtVandelay]

If the engine feels warm, I do a hot start.

[EricJ]

For a cold start I typically count to five running the boost pump.   For a hot start I don't use the boost pump at all (which is essentially Don's method).    For a "warm" start, somewhere in-between where I'm not sure a hot start will work, then anywhere from 1-3 seconds on the boost pump usually works well depending on how long it's been.

But, yes, "hot" start will work for quite a while after an airplane has been shut down.

 

[jaylw314]

2 hours ago, carusoam said:

Don has a video posted around here…

Essentially begin the start process with the mixture pulled… advancing slowly until the mixture is right… continue advancing as needed…

Find Don’s video it is short, sweet, and memorable…

Best regards,

-a-

It's still on YT 

 

[jaylw314]

3 hours ago, gwav8or said:

So I got my first experience with “hot start” yesterday. Temps were in the low 90s. CFI and I flew about an hour, stoped at a local airport to grab some lunch. Plane had sat for a little over an hour. After a few attempts we used Don Maxwells procedure and got it started.

That has me wondering. What’s the approximate time range for how long a hot start will be needed? Obviously OAT will play a factor. Seemed to me it should have cooled enough in an hour to not need hot start procedures. But this is my first fuel injected engine and I’m just trying to learn.

Hot starting has more to do with fuel than temperature.  On shutdown, the fuel in the lines above the motor warms up and pushes out the injectors into the intake manifold, so you have a mildly flooded intake.   Since the throttle is mostly closed, it can hang around for a surprisingly long time, even a couple hours.  On top of that, now you have no liquid fuel in the fuel lines, so it can take a few seconds for fuel to fill them up again even after the engine starts.

What you don't want to do is crank the motor with the throttle closed too much, give up after a few seconds and prime the intake to try a cold start.  You can end up flooding the intake even more.  That's the genius of Don Maxwell's technique, you keep the throttle open enough that only a few seconds of cranking should suck in enough air to light a typically flooded intake.  On the off chance that the motor doesn't catch in 5 seconds or so, it'd still be smart to open up the throttle and continue crank a couple more seconds to make sure you've cleared out the intake before trying a normal cold start.  Some people argue for flooding the engine to do a flooded start (which does of course work), but on the rare occasion DM's technique fails, I've never found that necessary, and a subsequent cold start always works out fine.

The empty fuel lines can result in the motor catching, opening the mixture, then having to wait a few seconds for the fuel to fill the lines while the prop spins freely.  Even though it seems like it won't happen, it almost always does, it's just a little unnerving.

[Vance Harral]

Due respect to Don, but the only hot start in that video is the first one, which he describes as "kind of a dirty start".  Every subsequent start he demonstrates is uninteresting, because the problems that cause hot starts require a couple of minutes or so to develop.  Shutting down the engine for 30 seconds and then restarting doesn't give enough time for the problems jaylw314 describes just above to actually develop.  Those only occur after the heat from the cylinders has a little while to "cook" the fuel in the lines into vapor.  The way I teach it, if you shut down at the pump, fuel up, and restart right away, it's generally not a hot start.  If you also need to pee and do it quickly, still not really a hot start.  If you get a cup of coffee, chat up the desk staff at the FBO, etc., you're looking at a genuine hot start.

[Shadrach]

13 minutes ago, Vance Harral said:

Due respect to Don, but the only hot start in that video is the first one, which he describes as "kind of a dirty start".  Every subsequent start he demonstrates is uninteresting, because the problems that cause hot starts require a couple of minutes or so to develop.  Shutting down the engine for 30 seconds and then restarting doesn't give enough time for the problems jaylw314 describes just above to actually develop.  Those only occur after the heat from the cylinders has a little while to "cook" the fuel in the lines into vapor.  The way I teach it, if you shut down at the pump, fuel up, and restart right away, it's generally not a hot start.  If you also need to pee and do it quickly, still not really a hot start.  If you get a cup of coffee, chat up the desk staff at the FBO, etc., you're looking at a genuine hot start.

So you prime after fueling?  
 

I don’t have problems with hot starts.  If an IO360 has been run in the previous 3 hours. I always initially try to start it without priming.  One can always add fuel if needed. 

[ArtVandelay]

So you prime after fueling?  
 
I don’t have problems with hot starts.  If an IO360 has been run in the previous 3 hours. I always initially try to start it without priming.  One can always add fuel if needed. 

Well, they’re hot starts, just not challenging hot starts.
I think the 10 minute (fuel stop) is the most challenging.
The 1-2 hour (oil change, long lunch) hot start isn’t bad because the engine isn’t so hot to percolate the fuel.

[Guest]

I believe that many of these hot starting issues are related to condition of the ignition system and the engine. Weak spark plugs, weak and mis-timed magnetos etc, weak battery, weak starter etc.  My IO-720, an engine reputed to have hot starting challenges, starts fine hot or cold.

[Sue Bon]

I open the throttle a touch more than for a cold start and turn on the boost pump. I just have to be careful to reduce throttle while going full rich to make sure RPM doesn't rev above 1100 during the start. This works for me whether the shutdown has been a few minutes or a couple of hours and in any temperature.

[alexz]

29 minutes ago, M20Doc said:

I believe that many of these hot starting issues are related to condition of the ignition system and the engine. Weak spark plugs, weak and mis-timed magnetos etc, weak battery, weak starter etc.  My IO-720, an engine reputed to have hot starting challenges, starts fine hot or cold.

I think You are 100% correct about about ignition system. Had a real trouble hot starting engine last week. Went and swapped too spark plugs on fresh new ones, while keeping bottom the same since they are fine wires- zero problems with hot start for the next 5 really hot starts with various time during shutdown (5 min to 45 min)

My observation spark plugs are good till 50-75 hours after that they need to be gapped and cleaned. If one happens to hit those 75 hours during hot weather - expect trouble. 

Let’s see if SureFly helps with a little. 

[M20F]

Full throttle, no mixture, fire, insert mixture, jiggle fuel pump a bit after mixture insertion if it starts to die.  Has yet to fail me unless I get a little slow on the uptake (miss the mixture or the pump if needed).  
 
When in doubt though just flood it.  Most folks wait far too long to flood and kill their battery/starter.  If you don’t get it by say third time, flood it. 
 
@carusoam is correct that outside temp has a big impact.  When I was basing up north it was a slightly different plan in the winter.  Now that I am in Dixie pretty much hot start whenever it flies and I need to retire. 

[RLCarter]

I could taxi from my hangar to the fuel pumps (1/4 mile, maybe) and the restart would require a “Hot Start” procedure. 

[ArtVandelay]

I open the throttle a touch more than for a cold start and turn on the boost pump. I just have to be careful to reduce throttle while going full rich to make sure RPM doesn't rev above 1100 during the start. This works for me whether the shutdown has been a few minutes or a couple of hours and in any temperature.

What’s so magical about 1100 rpm limit on a hot start?

[PT20J]

I use a variation of the technique developed on the big radials that were notoriously difficult to start hot or cold. It's called the controlled quantity start. It takes fuel and air in the proper proportions to ignite. The idea is to keep the air constant while controlling the amount of fuel. This is done by opening the throttle somewhat and leaving it fixed during the start. The exact amount of throttle isn't important (I open it about a quarter inch), but what is important is to not touch it during the start. I start cranking with the mixture in ICO. If there is enough raw fuel in the lines and cylinders (as in a restart soon after shut down) it will start in ICO and then I advance the mixture to keep it running and adjust the throttle to set the idle speed. If it doesn't start immediately, I keep cranking and slowly advance the mixture control until enough fuel is admitted and the engine starts. 

Skip

[Ragsf15e]

Look, if it’s even slightly warm, maybe even if I flew it 5 hours ago on a warm day, I’m not gonna prime it.  Just crank it and it’ll start.  Or use @PT20J method on that one and it’s fine.  If it doesn’t start, no harm, now you can move on to a normal start.  If you prime it first, you can never “un prime” it.  You will be stuck in a flooded start.
 

You can always prime and try a normal start after a missed hot start, but the reverse is not true.

Another thing is that a flooded start is occasionally necessary, but shouldn’t be a first choice or a “go to” method.  There’s some increased risk of a tailpipe fire.  There’s a few 100 threads on this.  One on tailpipe fire too…

Good ignition system is important, but technique and strategy are equally so.  You won’t get it started without any of those.

[Sue Bon]

1 hour ago, ArtVandelay said:

What’s so magical about 1100 rpm limit on a hot start?

I was just taught not to let the engine rev over 1100 rpm during any start. Apparently it's not good for the camshaft...???

[Ragsf15e]

7 minutes ago, Sue Bon said:

I was just taught not to let the engine rev over 1100 rpm during any start. Apparently it's not good for the camshaft...???

I love that!  You’re my hero for this!  I wouldn’t say it’s a hard and fast number, but you definitely don’t want to be like 90% of the Cirrus drivers and start your engine at takeoff power and let it run there for the next 20” while trying to figure out what button/knob/soft key to push to make the loud noise stop.  Pet peeve of mine, starting at takeoff power.

I think the long and short is that it’s not good to go above normal idle until you’ve assured good oil pressure.  1000-1200ish is all good.  Someone with more engine knowledge will help me out on that.

[TheAv8r]

53 minutes ago, PT20J said:

I use a variation of the technique developed on the big radials that were notoriously difficult to start hot or cold. It's called the controlled quantity start. It takes fuel and air in the proper proportions to ignite. The idea is to keep the air constant while controlling the amount of fuel. This is done by opening the throttle somewhat and leaving it fixed during the start. The exact amount of throttle isn't important (I open it about a quarter inch), but what is important is to not touch it during the start. I start cranking with the mixture in ICO. If there is enough raw fuel in the lines and cylinders (as in a restart soon after shut down) it will start in ICO and then I advance the mixture to keep it running and adjust the throttle to set the idle speed. If it doesn't start immediately, I keep cranking and slowly advance the mixture control until enough fuel is admitted and the engine starts. 

Skip

This method works really well in my E model, after playing with all the hot start methods. I start cranking and very slowly advance the mixture from ICO, once it catches, I slowly add more, maybe half-in or so and then adjust from there for smooth running. 

[TheAv8r]

1 minute ago, Ragsf15e said:

I love that!  You’re my hero for this!  I wouldn’t say it’s a hard and fast number, but you definitely don’t want to be like 90% of the Cirrus drivers and start your engine at takeoff power and let it run there for the next 20” while trying to figure out what button/knob/soft key to push to make the loud noise stop.  Pet peeve of mine, starting at takeoff power.

I think the long and short is that it’s not good to go above normal idle until you’ve assured good oil pressure.  1000-1200ish is all good.  Someone with more engine knowledge will help me out on that.

I always thought this was more related to Oil Temperature rather than pressure. You don't want to run the engine at a high RPM if it's cold and the oil is super thick as it's harder to get that oil to coat all surfaces, better to run at 900-1000rpm until the Oil Temps warm up. I think that same principle would apply with starting at a high RPM. 

[Sue Bon]

9 minutes ago, Ragsf15e said:

I love that!  You’re my hero for this!

Oh my gosh. I was so nervous saying anything about engines at all! I will sleep well tonight  

[ArtVandelay]

Since we’re talking about hot starts, oil is hot, and all internal parts are covered with oil, so I don’t see any reason to limit starting RPMs, staying within reason of course. If you ever do a flooded start you’ll exceed that 1100 by a lot.
I think higher RPMs help stabilize the engine since your pumping more fuel and cooling air and therefore cooling the fuel lines. I’m not talking 2000+, but 1200 seems enough. I give it a few seconds to settle down and then reduce power to 1000.