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Starting Hot Engine with Dual PMags

Tankerpilot75

Tankerpilot75

Well Known Member
I’m having trouble re-starting my engine after shutdown for refueling.

I’ve got a Superior IO-360 with dual PMags which are timed at 3 teeth (~ 6* ATDC). The PMag manual says:
a) MasterON.
b) Openthrottle1⁄4”
c) Mixture

(1) Cold Engine:
1. Mixturefullrich.
2. BoostpumpONuntilpressurerisesthenOFF.
. 3. Returnmixturetolean.

(2) Hot Engine:
1. Leavemixturelean.
2. Noboost.
d) Crankuntilfirstfire(typically3to4blades).

Following the Hot Engine procedure it just won’t start and if it initially tries, it runs rough then dies. The air temperatures were high (102 degrees) so I’m sure fuel vaporization inside a hot engine compartment is occurring.

A friend suggested leaving the mixture off, throttle full forward, boost pump on to get cooler fuel to the throttle body, boost pump off, throttle set to 1/2 then start. Feed in mixture once started.

Frankly this seems to me that I’d likely flood everything. But obviously the PMag manual procedure isn’t working.
 
I have a new to me IO-375 with dual P-Mags. It's summer in FL and I've been getting plenty of hot start practice. I had one hot start attempt that did not go well but since then, I've found a method that seems to be working consistently.

When hot, I push both the throttle and mixture in full and leave them full for 10 to 12 seconds.

I then return the throttle to just cracked and the mixture to cutoff. With the mixture in cut off, I hit the boost pump for about two seconds and then boost pump off.

I then engage the starter and when the engine catches, I slowly walk the mixture in to full.

About 50% of the time, the engine will start to quit after the mixture is fully in. When this happens, I turn the boost pump on and this has kept the engine from quitting. I leave the boost pump on for a minute or so, until the engine seems stable.

I've read a lot of past threads on the topic. Everyone has a procedure that they swear by. Each is slightly different.

The above seems to be working for me.
 
You are correct, fuel vaporization inside a hot engine compartment is occurring.
The problem is that the fuel lines are hot and does not contain liquid fuel.
It is important that fuel lines are insulated as much as possible.
Fire sleeve the fuel lines if not already done. This will help.
Other than that, moving cold fuel through the line with the electric fuel pump will provide liquid fuel to the servo.
However this may flood the engine unless full throttle is used.
Moving aircraft into wind and wait 30 minutes will help.
If you need professional advice to overcome this problem contact
Don Rivera.

https://airflowperformance.com/index.php/contact/

Good luck
 
Jim, try this method for your hot start. It is the most successful method for me and when all others fail.

(2) Hot Engine:
1. Leave mixture fully lean.
2. WO throttle
2. Noboost.
d) Start cranking and while cranking pull the throttle slowly to close. At some point the air to fuel mixture will be just right for it to start. At that point push the mixture in slowly.
 
Bavafa said:
Jim, try this method for your hot start. It is the most successful method for me and when all others fail.

(2) Hot Engine:
1. Leave mixture fully lean.
2. WO throttle
2. Noboost.
d) Start cranking and while cranking pull the throttle slowly to close. At some point the air to fuel mixture will be just right for it to start. At that point push the mixture in slowly.
Click to expand...

I was having a lot of trouble restarting the engine after my magnetometer calibration and I remembered reading something like this on VAF a long time ago. After a couple of catches, the engine started and remained running. The throttle was about 1/2 way closed when the engine catch
 
Bavafa said:
Jim, try this method for your hot start. It is the most successful method for me and when all others fail.

(2) Hot Engine:
1. Leave mixture fully lean.
2. WO throttle
2. Noboost.
d) Start cranking and while cranking pull the throttle slowly to close. At some point the air to fuel mixture will be just right for it to start. At that point push the mixture in slowly.
Click to expand...

I am very similar to this, but go about 1/2 throttle instead of full, once engine catches I slowly increase mixture, pull back throttle.
 
I have used these procedures to start thousands of Lycoming Io-360 engines successfully.
Procedure for a cold engine:
(1) Set propeller governor control in "Full RPM" position (where
applicable).
(2) Turn fuel valve "On".
(3) Open throttle wide open, move mixture control to "Full Rich"
turn boost pump on, approximately 3 to 5 seconds, turn boost pump off,
then return throttle to "Closed" and return mixture control to
"Idle Cut-Off".
(4) Open throttle 1/4 to 1/2 of travel. Keep you hand on the throttle during the staring process to make movement toward the idle position after the engine has started an easy immediate thing to be able to do.
(4) Set magneto selector switch (consult airframe manufacturer's
handbook for correct position).
(5) Engage starter.
(6) Engine starts.
(7) Retard throttle towards idle position.
(8) Move mixture control slowly and smoothly to "Full Rich".
(9) Check oil pressure gage. If minimum oil pressure is not indicated
within thirty seconds, stop engine and determine trouble.


Procedure for a hot engine that was shut down within a few minutes ago:
(1) Set propeller governor control in "Full RPM" position (where
applicable).
(2) Turn fuel valve "On".
(3) Open throttle wide open, move mixture control to "Full Rich"
return throttle to "Closed" and return mixture control to
"Idle Cut-Off".
(4) Open throttle 1/4 to 1/2 of travel. Keep you hand on the throttle during the staring process to make movement toward the idle position after the engine has started an easy immediate thing to be able to do.
(4) Set magneto selector switch (consult airframe manufacturer's
handbook for correct position).
(5) Engage starter.
(6) Engine starts.
(7) Retard throttle towards idle position.
(8) Move mixture control slowly and smoothly to "Full Rich".

Procedure for a hot engine that was shut down more than a couple of minutes ago:
(1) Set propeller governor control in "Full RPM" position (where
applicable).
(2) Turn fuel valve "On".
(3) Open throttle wide open, move mixture control to "Full Rich"
turn boost pump on, approximately 1 second or less, turn boost pump off,
then return throttle to "Closed" and return mixture control to
"Idle Cut-Off".
(4) Open throttle 1/4 to 1/2 of travel. Keep you hand on the throttle during the staring process to make movement toward the idle position after the engine has started an easy immediate thing to be able to do.
(4) Set magneto selector switch (consult airframe manufacturer's
handbook for correct position).
(5) Engage starter.
(6) Engine starts.
(7) Retard throttle towards idle position.
(8) Move mixture control slowly and smoothly to "Full Rich".

Try them I am sure they will work for you.
Good Luck, Mahlon
 
Last edited:
mahlon_r said:
I have used these procedures to start thousands of Lycoming Io-360 engines successfully.
Procedure for a cold engine:
(1) Set propeller governor control in "Full RPM" position (where
applicable).
(2) Turn fuel valve "On".
(3) Open throttle wide open, move mixture control to "Full Rich"
turn boost pump on, approximately 3 to 5 seconds, turn boost pump off,
then return throttle to "Closed" and return mixture control to
"Idle Cut-Off".
(4) Open throttle 1/4 to 1/2 of travel. Keep you hand on the throttle during the staring process to make movement toward the idle position after the engine has started an easy immediate thing to be able to do.
(4) Set magneto selector switch (consult airframe manufacturer's
handbook for correct position).
(5) Engage starter.
(6) Engine starts.
(7) Retard throttle towards idle position.
(8) Move mixture control slowly and smoothly to "Full Rich".
(9) Check oil pressure gage. If minimum oil pressure is not indicated
within thirty seconds, stop engine and determine trouble.


Procedure for a hot engine that was shut down within a few minutes ago:
(1) Set propeller governor control in "Full RPM" position (where
applicable).
(2) Turn fuel valve "On".
(3) Open throttle wide open, move mixture control to "Full Rich"
return throttle to "Closed" and return mixture control to
"Idle Cut-Off".
(4) Open throttle 1/4 to 1/2 of travel. Keep you hand on the throttle during the staring process to make movement toward the idle position after the engine has started an easy immediate thing to be able to do.
(4) Set magneto selector switch (consult airframe manufacturer's
handbook for correct position).
(5) Engage starter.
(6) Engine starts.
(7) Retard throttle towards idle position.
(8) Move mixture control slowly and smoothly to "Full Rich".

Procedure for a hot engine that was shut down more than a couple of minutes ago:
(1) Set propeller governor control in "Full RPM" position (where
applicable).
(2) Turn fuel valve "On".
(3) Open throttle wide open, move mixture control to "Full Rich"
turn boost pump on, approximately 1 second or less, turn boost pump off,
then return throttle to "Closed" and return mixture control to
"Idle Cut-Off".
(4) Open throttle 1/4 to 1/2 of travel. Keep you hand on the throttle during the staring process to make movement toward the idle position after the engine has started an easy immediate thing to be able to do.
(4) Set magneto selector switch (consult airframe manufacturer's
handbook for correct position).
(5) Engage starter.
(6) Engine starts.
(7) Retard throttle towards idle position.
(8) Move mixture control slowly and smoothly to "Full Rich".

Try them I am sure they will work for you.
Good Luck, Mahlon
Click to expand...

+1

after the initial heat soak, the fuel boils out of the lines and is pushed into the intake chamber. However, after a period of time it evaporates. If that fuel is still in the chamber it may kick and run. If it evaporates, you now have a void. If I can't get it on the first try, I go mixture rich and BP for 1 sencond, then ICO and start. This step refills the lines and puts on overly rich mix in the chamber. It may take several seconds, but IT WILL kick over with this method. Strongly discourage the Full throttle approach. If you get distracted and don't have a lot of pressure on the brakes, you can easilly start moving and go somewhere you didn't intend.
 
A hot mechanical FI engine is almost always in a flooded/too rich condition within about a minute of shutdown no matter what. If you understand and accept that basic truth you can move directly into the "clear engine" procedure and get the engine back to the baseline (lean) condition. Good news: the "clear engine" procedure almost always results in an engine start.

The clear engine process is the same for a car, tractor, lawnmower and airplane - Sweep the excess fuel out the exhaust. One typically does this by rotating the engine and introducing air. Some have done the throttle sweep thing while hunting for some magic sweet spot in throttle position that yields a combustible mixture but I have found that the real element is "time". Grind on the stater with the throttle wide open or cracked - makes no difference except the speed at which you flush the mixture out. WOT makes things happen faster; including the reaction when the engine DOES catch!

If the engine catches during the clear engine procedure, be ready to shove the mixture in to keep it running, but don't be in a rush! If it's chugging and blubbering, it's telling you that it's still very rich. It will smooth out as it cleans out and then die as it goes lean. Bring the mixture in at the "clean out" stage. If it dies on you after the clean out stage, NOW you are at your lean engine baseline and can do the normal engine start.

Bottom line: A hot engine is a flooded engine. Your goal is to clear it out and get to baseline. If you're good, the engine starts.
 
Question: How to shutdown with lean condition

Toobuilder said:
A hot mechanical FI engine is almost always in a flooded/too rich condition within about a minute of shutdown no matter what. .
Click to expand...

Thanks for the write up! . Question: is there a method to shutdown a FI engine so it will be in a "lean" condition for the next restart? Like to shutdown for refueling? Is shutting down with the fuel valve in the OFF position help?
 
PhatRV said:
Thanks for the write up! . Question: is there a method to shutdown a FI engine so it will be in a "lean" condition for the next restart? Like to shutdown for refueling? Is shutting down with the fuel valve in the OFF position help?
Click to expand...

One would have to find a way to evacuate all traces of fuel from the injector lines at shutdown. Any fuel remaining will dribble out the injectors.

That said, clearing a flooded engine is not difficult and should certainly not be a source of anxiety on the ramp. Unless you make the flooded situation worse by running boost and trying to "overprime", then the engine should clear/start within 5 seconds of rotation on the starter. If you go to 10 seconds without a pop, then the engine is most likely "lean/baseline" (or something else broke)
 
Last edited:
Hi Mahlon, did you paste in the same instructions for all three scenarios, or am I just missing the differences...

With my io-360 which is awsome, and I bought from Mahlon, I use the WOT/ICO process and swap both when it catches. I also have the AFP with fuel purge, which I often use to flush fresh, cool fuel into the system before starting. I have tested both with and without the fuel purge, and can get it started pretty easily using the "goldilocks - sweep" method.

And before anyone says "sure, but it's not hot in Switzerland" - I've attached a photo of the temperature inside my hangar from the other day. :)

IMG_9865.jpg
 
rv8ch said:
Hi Mahlon, did you paste in the same instructions for all three scenarios, or am I just missing the differences...

With my io-360 which is awsome, and I bought from Mahlon, I use the WOT/ICO process and swap both when it catches. I also have the AFP with fuel purge, which I often use to flush fresh, cool fuel into the system before starting. I have tested both with and without the fuel purge, and can get it started pretty easily using the "goldilocks - sweep" method.

And before anyone says "sure, but it's not hot in Switzerland" - I've attached a photo of the temperature inside my hangar from the other day. :)

View attachment 47025
Click to expand...

all three are basically the same with different boost pump settings for each.
Good L:uck,
Mahlon
 
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