Hot start procedures for IO-360

[LeRoy Johnston]

Hi all--New Mooney owner here (1996 M20J MSE).  I am having hot start issues.  The book says crack throttle, mixture lean, crank till it starts and move mixture smoothly to rich.  My engine coughs a few times and I move the mixture to rich but it doesn't start.  What procedures have you had good success with?   Any advice will be much appreciated.  

[N201MKTurbo]

Go about 1/4 throttle with the mixture at cutoff. Crank till it starts and when it starts to die advance the mixture. Do this without the boost pump. The engine is always flooded after shutdown, so you are doing a flooded start. Use this procedure for about 4 hours after shutdown.

[N201MKTurbo]

9 minutes ago, LeRoy Johnston said:

Hi all--New Mooney owner here (1996 M20J MSE).  I am having hot start issues.  The book says crack throttle, mixture lean, crank till it starts and move mixture smoothly to rich.  My engine coughs a few times and I move the mixture to rich but it doesn't start.  What procedures have you had good success with?   Any advice will be much appreciated.  

When it coughs, it is just getting lean enough to run, don't advance the mixture until it starts.

[McMooney]

set to 1000ish rpm at shutdown, leave it there. 

Assuming the engine is still hot when you return, leave everything as it was on shutdown and just try to start the plane.

it should start almost immediately, advance mixture once it starts.

if you miss the start after a couple tries, save your self a headache and just flood the engine and perform a flooded start.

[toto]

 

[LeRoy Johnston]

Thanks much! --LeRoy

[ArtVandelay]

it should start almost immediately…

In my experience that occurs if it’s only been a couple of minutes, like in the Maxwell video.
If it’s hot and been 10 minutes what happens is all the fuel has percolated out and it will take ~5 seconds to reenergize the fuel lines.
If at higher density altitude, you’ll flood it if you go full rich, so adjust accordingly.
If your starter is not turning over with enthusiasm you’ll take more than 5 seconds.
Every starting problem because of mechanical issues I have had (2 bad starters, clogged fuel drain, 1 bad battery) occurred on a restart. Hot restarts are a good stress test.

[LeRoy Johnston]

Thanks again.  Curious why does it start with the mixture at idle cut-off when that is what you do to stop the engine. 

[jaylw314]

The fuel injector rails are above the engine which is the cold side in flight.  After shutdown, though, the top gets hot and the remaining fuel in the lines heats up, causing it to vaporize out into the intake manifold, so you end up with too much fuel and too little air there (flooded).  with the throttle near closed, it'll stay that way for a while (a couple hours?).  A hot start uses that fuel to start, so you don't need to add any extra.  Since it's flooded, though, you have to suck enough air in by cranking to get the right balance, hence some techniques that involve opening the throttle 1/4 or even fully open.  The more flooded the intake, the more open you need the throttle, otherwise you'd be waiting forever.

In the video above, there hasn't been a whole lot of time to leak out a lot of fuel, so leaving the throttle mostly closed to 1000 RPM (I only need a tiny amount, about 1/4", to get 1000 RPM) is good.  If you come back when most of the fuel has leaked out 10-15 minutes later, you might need more throttle or cranking a bit longer.  After that, enough fuel evaporates away that the 1000 RPM throttle setting is good again.  So the rule of thumb to set it to 1000 RPM before shutting down seems to work in most cases.

FWIW, a difficulty with hot starts is that now there is vapor in the fuel lines, so when you advance the mixture, it takes a few extra seconds for the proper amount of fuel to come out the injectors.  If it catches, runs, but stumbles and dies when you advance the mixture, that might be why.  A solution is to just go ahead and fully flood the intake with the mixture full and pump on for 3-5 seconds, and do a proper flooded start.  Tougher on the starter, but at least you know the fuel lines are full when it catches.

If you're still having problems, check the ignition/spark plugs, too.  Really, with typical hot starts the IO-360 should start up in about 3-4 turns, you shouldn't have to sit there cranking away...  

[jaylw314]

2 hours ago, LeRoy Johnston said:

Hi all--New Mooney owner here (1996 M20J MSE).  I am having hot start issues.  The book says crack throttle, mixture lean, crank till it starts and move mixture smoothly to rich.  My engine coughs a few times and I move the mixture to rich but it doesn't start.  What procedures have you had good success with?   Any advice will be much appreciated.  

Oh, and congratulations/welcome! 

[81X]

3 minutes ago, jaylw314 said:

The fuel injector rails are above the engine which is the cold side in flight.  After shutdown, though, the top gets hot and the remaining fuel in the lines heats up, causing it to vaporize out into the intake manifold, so you end up with too much fuel and too little air there (flooded).  with the throttle near closed, it'll stay that way for a while (a couple hours?).  A hot start uses that fuel to start, so you don't need to add any extra.  Since it's flooded, though, you have to suck enough air in by cranking to get the right balance, hence some techniques that involve opening the throttle 1/4 or even fully open.  The more flooded the intake, the more open you need the throttle, otherwise you'd be waiting forever.

In the video above, there hasn't been a whole lot of time to leak out a lot of fuel, so leaving the throttle mostly closed to 1000 RPM (I only need a tiny amount, about 1/4", to get 1000 RPM) is good.  If you come back when most of the fuel has leaked out 10-15 minutes later, you might need more throttle or cranking a bit longer.  After that, enough fuel evaporates away that the 1000 RPM throttle setting is good again.  So the rule of thumb to set it to 1000 RPM before shutting down seems to work in most cases.

FWIW, a difficulty with hot starts is that now there is vapor in the fuel lines, so when you advance the mixture, it takes a few extra seconds for the proper amount of fuel to come out the injectors.  If it catches, runs, but stumbles and dies when you advance the mixture, that might be why.  A solution is to just go ahead and fully flood the intake with the mixture full and pump on for 3-5 seconds, and do a proper flooded start.  Tougher on the starter, but at least you know the fuel lines are full when it catches.

If you're still having problems, check the ignition/spark plugs, too.  Really, with typical hot starts the IO-360 should start up in about 3-4 turns, you shouldn't have to sit there cranking away...  

I use the cutoff mixture method for hot starts on my TSIO360 and @LeRoy Johnston ‘s question had me perplexed as well, thanks for the explanation as to why/how it works, @jaylw314!  
 

I also run the boost pump for 5-7 seconds at cutoff to pressurize the lines (and circulate out vapor?) before attempting to crank. Works great about 100% of the time on hot starts. 
 

[Bolter]

If it helps, on my J, the ideal hot start throttle opening is where it clicks for the gear warning horn.  I push the throttle until the I hear/feel the switch click.  YMMV, but for me that gives something a little more repeatable than "about a 1/4"" or "crack the throttle a little".  

[jaylw314]

25 minutes ago, 81X said:

I use the cutoff mixture method for hot starts on my TSIO360 and @LeRoy Johnston ‘s question had me perplexed as well, thanks for the explanation as to why/how it works, @jaylw314!  
 

I also run the boost pump for 5-7 seconds at cutoff to pressurize the lines (and circulate out vapor?) before attempting to crank. Works great about 100% of the time on hot starts. 
 

Just as a reminder, your TSIO-360 is a Continental which has a different fuel injection system--there's a fuel return line, so unused fuel is returned to the fuel tank.  Running the boost pump before hot starts does actually flush bubbles out before some point in the system (I don't know enough about them), so is apparently good technique.

Lycomings don't have a fuel return line, so with the mixture closed, the pump doesn't really clear anything out, and it's nowhere near enough pressure to liquefy the vapors.

[jaylw314]

2 minutes ago, Bolter said:

If it helps, on my J, the ideal hot start throttle opening is where it clicks for the gear warning horn.  I push the throttle until the I hear/feel the switch click.  YMMV, but for me that gives something a little more repeatable than "about a 1/4"" or "crack the throttle a little".  

That's funny, I think I do that too, I just have never thought about it, although the process defies precision anyways...

Edited September 21, 2021 by jaylw314

[ohdub]

For mine I've found that what works every time is to shut down with the throttle at 1,300 RPM. When I start cranking, I slowly advance the mixture until it starts-usually with the mixture about 1/4 to 1/2 the way in. I don't know why that works for me and that other suggested techniques don't? But that's what I do now and it never fails.

[thomas1142]

All great advice, just like I received when I was new to my 97 M20J and having starting issues. But for me nothing worked I was so frustrated I was ready to put a for sale sign on it. I was "stranded" for hours on three different occasions till I was able to start it. Once I could not start it on my home field, called the mechanic (AI), but by the time he came over I managed to start it. Got the same advice from him; patience you are new, and  you will learn. 

On the last "stranded" event I had the mechanic look over the aircraft real good. Did a timing test on it and he said he could not believe it even started at all by how far off the timing was. Had the AP try to set the timing on it, he could not, so the AI tried and had a hard time. Removed the magneto to find that the cap was rotating a full 1/4 to 3/8 of an inch. One Mag almost shot, the other barely firing, but my preflight runups were fine.

Moral to this story: if you are doing everything right, and all the advice you are getting isn't working, maybe its not you.  Get your plane checked before it frustrates you like it did me.

[FloridaMan]

If you're having issues. Get a Slickstart. The only time my M20F has had issues starting are when the left mag has failed or the wire connected to the SlickStart has fallen off. Supposedly the Surefly provides good starting as well, but I don't have one on my M20F. 

[jaylw314]

2 hours ago, ohdub said:

For mine I've found that what works every time is to shut down with the throttle at 1,300 RPM. When I start cranking, I slowly advance the mixture until it starts-usually with the mixture about 1/4 to 1/2 the way in. I don't know why that works for me and that other suggested techniques don't? But that's what I do now and it never fails.

Whatever works  The potential problem with that technique is that if the motor doesn't happen to catch, you won't know that you've flooded the engine.  On the other hand, flooded starts should be non-issues.

Also, 1300 RPM is a little spicy for anyone standing behind you.  Probably not enough to be dangerous or anything, but I'm guessing you pull it back quickly when it starts

[LeRoy Johnston]

Great discussion--My mechanic (who owned an M20J for years), deliberately floods it so every warm start is a flooded start.  The idea is to start from a known condition.   We tried that too and it worked for me the first time but not the next day.   It's a little sporty because you need to be ready to back off the throttle.   Because it is not starting 100 percent reliably, we are going to do a complete ignition service--overhaul mags (at 500 hours they are due now anyway), new plugs with fine wires on the bottom, and of course set timing and check engine controls.  We know it's getting air and fuel, so this may be the answer.   I have learned a lot about the system from reading these posts, for which I am indebted to you all.  --LeRoy 

[LeRoy Johnston]

Great discussion--My mechanic (who owned an M20J for years), deliberately floods it so every warm start is a flooded start.  The idea is to start from a known condition.   We tried that too and it worked for me the first time but not the next day.   It's a little sporty because you need to be ready to back off the throttle.   Because it is not starting 100 percent reliably, we are going to do a complete ignition service--overhaul mags (at 500 hours they are due now anyway), new plugs with fine wires on the bottom, and of course set timing and check engine controls.  We know it's getting air and fuel, so this may be the answer.   I have learned a lot about the system from reading these posts, for which I am indebted to you all.  --LeRoy 

[LeRoy Johnston]

I'm going to look into that Slickstart product, too.  --LeRoy

[ArtVandelay]

If you're having issues. Get a Slickstart. The only time my M20F has had issues starting are when the left mag has failed or the wire connected to the SlickStart has fallen off. Supposedly the Surefly provides good starting as well, but I don't have one on my M20F. 

How does slickstart fix hot starts because hot starts are a fuel supply problem, not a spark problem?

[ohdub]

49 minutes ago, jaylw314 said:

Also, 1300 RPM is a little spicy for anyone standing behind you.  Probably not enough to be dangerous or anything, but I'm guessing you pull it back quickly when it starts

It never gets to 1,300, once it starts I pull the throttle back and it never goes over 1,000 RPM.

[WaynePierce]

McMooney posted exactly what I was going to say and someone else posted the video I was going to reference. When you shut down properly... idle to 1000 and lean to cut off, when you get back in after refueling or a very short stop, Don't Touch Anything but the key and start, it will almost start immediately then smoothly go from lean cut-off to rich (in my case about an inch out of full rich) and it works every time. 1985 J model.

 

[PT20J]

Some of the mystery disappears with a bit of thinking about how the fuel injection system works. First of all, the engine will only start when the fuel-air mixture is within a combustible range. During start, the throttle controls the air and the mixture controls the fuel. It's best to crack the throttle and only mess with the mixture control so that you are only dealing with one variable. When you shut the engine down with the mixture control, you shut off fuel to the injectors at the fuel servo. The flow divider on top of the engine has a poppet valve that closes when the pressure drops and this shuts off the fuel to all the injector lines simultaneously to get a clean shutdown. This stops the flow to the injectors, but leaves fuel trapped in the lines.

When you start the hot engine after it has sat for only a few minutes, the fuel trapped in the injector lines has been heated by the engine and some of it has formed gas bubbles which have expanded and forced the liquid fuel out through the injectors. It is the same as if you had primed a cold engine. This is why if you crack the throttle and crank the starter with the mixture in ICO it will start. Of course, if you don't richen the mixture it will soon run out of this fuel and stop. However suppose you let the hot engine sit longer -- say 30 minutes to an hour. The heat will have boiled all the gas out of the injector lines and it will have evaporated. Now the hot engine is not primed. In this case, crank with the throttle cracked and the mixture in ICO and if it doesn't start, keep cranking and slowly advance the mixture control until it fires. What you are doing is keeping the air constant and gradually introducing fuel until the mixture gets within the combustible range. 

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