Starting a hot engine?

[TotalBeginner]

Can anyone provide a link or give some tips on the best way to start a hot engine? I made a quick pit stop to collect a passenger today and as the engine had only been shut down 15 minutes I had a hard time getting it started. I've looked on the lycoming website but can't find anything relevant.

Many thanks!

[jxk]

It kinda depends on what type of aircraft and engine eg fuel injected.

[TotalBeginner]

It kinda depends on what type of aircraft and engine eg fuel injected.

Doh! I guess that would help! :rolleyes:

It's a PA28-181 Archer III (lycoming 0-360-A4M)

[jxk]

I would just push the throttle in a couple of times (no primer) this will squirt a minimum about of fuel into the venturi and crank with the throttle set just forward of the cold start position. Oh and crossing your fingers helps!

[Fright Level]

The definitive answer is in the POH which should be onboard. Many engines have a different technique for hot starts. I've always found hot engines to start on the button if the correct method is used (even if I have only dug out the manual after cranking for a couple of minutes with no joy).

[shortstripper]

I find many people try too hard to start a "hot" engine. Often, no priming and throttle closed does the trick whereas priming/pumping, throttle set ect is just too much.

SS

[TotalBeginner]

The POH said that the throttle should be said to 1/2" open (as opposed to 1/4" with a cold engine) but made no other recommendations. Maybe I was just unlucky?

[echobeach]

I found it very difficult doing a hot start last weekend in a fuel injected Arrow. I have flown a different Arrow for a year, that always started with no problems hot or cold.

Flew a different Arrow last weekend. On the 4th hot start of the day following exactly the POH instructions it would not start. After so many starts with no problem I could not believe I might get stuck far from base. In the past after a few attempts when I thought I had flooded the engine I found that that opening throttle fully and then mixture ICO to full when firing always worked, but even this failed.

I don’t know why this was so difficult. Started in the end but lost some of my confidence with hot starts. Any thoughts ?

[IO540]

The fuel servo might need a service.

Most rental spamcans are knackered, and most maintenance companies don't understand the "technical" stuff like fuel injection. Their expertise is so often limited to squirting aerosol oils into bearings.

Working on fuel servos is specialised work; not many firms in the UK do it and it's not cheap - a few hundred quid just to adjust one screw to e.g. set up the full power fuel flow. Almost nobody will want to pay for this, all the time the plane gets off the ground.

My TB20 cold starts instantly, and hot starts every time after some cranking - using the POH procedures. Never failed. Though I have to say that the new Skytec lightweight starter does do it quicker because the engine goes round at least twice as fast as previously.

[echobeach]

IO. I can see an emerging theme from your recent posts and I think I can see the sense in this. The rental market seems to have many frustrations and when possible I think purchase/group only way forward.

[jxk]

The Archer has an O engine and therefore isn't fuel injected; just a good old fashioned carb! Fuel injected engines need different techniques.

[172driver]

There are just too many variables to give a blanket advice here, every installation is different and has its own quirks.

As a general rule (now contradicting my own words above ;) ) however, you can rarely go wrong with a hot engine by starting the process from totally lean. IOW, no primer, throttle just a tiny bit open, crank and perhaps (if you sense the engine is about to 'come') push throttle a couple of times while turning over. Usually works for carb engines. YMMV......

[mad_jock]

Ok as an ex instructor pa 38/28 and that heap of crap the c172.

Mix max, throttle closed.

Under no attempt touch the primer if you even look at it walk away for 30mins.


Wind it over when it catches give a ball hair of throttle.

No pumping of the lever.
No fannying about with any other lever.
If the primer is unlocked on a hot engine to require start the engine is fecked.

mixture rich throttle zero with a small advance when it kicks in.

If in doudt call it a **** while turning

[RTN11]

read the POH.

do not pump the throttle, as the aircraft is fitted with a primer, use that if you need to prime, which you shouldnt need to if it's only been shut down for 15 mins.

Pumping the throttle puts an unmeasured amount of fuel right next to the cylinder, the amount will vary depending on how hard/fast you pump the throttle, which seriously increases the chances of an engine fire.

They wouldn't fit a primer if they wanted you to prime it using the throttle.

The throttle does need to be set more open than a cold start for a PA-28.

[SNS3Guppy]

Most rental spamcans are knackered, and most maintenance companies don't understand the "technical" stuff like fuel injection. Their expertise is so often limited to squirting aerosol oils into bearings.


As a long time mechanic and inspector, I've never personally seen a shop filled with mechanics ("engineers" to you) so stupid and inept that they are unable to maintain an injected engine, or who find it too "technical." Surely you must have found the most inept on earth.

I've worked for several companies instructing and flying charter and flying maintenance in rental airplanes, and haven't flown any that are "knackered," or maintained by those who can't fathom the increadibly simple fuel injection systems that the airplanes use...or carbureted systems, for that matter.

You truly know mechanics who can do nothing more than "squirt aerosol oils into bearings?" Report them immediately...and then trap them under glass. You've discovered a rare, primitive breed, the likes of which is seldom to be found. Most I know are professionals who do far more than "squirt aerosol oils into bearings."

IO. I can see an emerging theme from your recent posts and I think I can see the sense in this.


As can I; a strong theme of arrogance which presupposes a lot of incorrect information. Some might call it self-righteousness.

Pumping the throttle does two things; it opens the air valve known as the throttle, and on some engines it activates the accelerator pump. It does NOT prime the engine.

If you need prime, use prime.

If the manufacturer recommend method for starting an engine which is heat soaked isn't working, then you may either be doing it incorrectly, or you may have components in need of replacement or adjustment.

Use caution moving or being around the propeller when the engine is hot. At all times, really, but I've seen some who feel that if it won't fire off right away with the starter, then they're okay to move the propeller by hand. I've seen some who flood the engine, then pull it through by hand for some inexplicable reason, prior to hand cranking again. Don't do it, if someone recommends the practice to you.

If the engine isn't firing, consider what makes it fire, and look at what you can do to change your choices. The engine requires fuel, air, and spark. Some engines are started on one magneto because of a shower of sparks system or impulse coupling and to prevent unwanted action by the other mag due to a timing difference or for other reasons. Note the requirements of your engine installation as spelled out in the aircraft flight manual and any relevant supplements. If you have a weak spark plug, with an incorrect gap or too high resistance, or slightly or largely fouled, it may be affected by the temperature increase or the change in location (launching from a different elevation, for example). Old spark plug leads experience a change in resistance when exposed to heat, as well. A magneto, condensor, coil, and other components may also experience changes in properties in the presence of heat...these are things you can't control as a pilot, but which may prevent spark. Corrosion in spark plug leads or attaching components, burned and pitted points, etc, also affect this, as does incorrect internal mag timing or mag-to-engine timing.

Airflow can be impeded by a dirty filter, or the formation of carb ice...which can form even during the engine start under some conditions. If you're unable to obtain a start through the normal filtered air, try it with carb heat on or your alternate air. It's one change you can easily make which may on some occasions make a difference.

You can help vent some heat from the engine by leaving the oil filler door and other doors open on the nacelle or cowl when you're away from it...but use caution so as to not forget the doors and lose one in flight later. I've seen that happen a few times. I've also seen folks cover the intake as part of a post flight, only to forget it on start up. The engine needs air to breath, just like you and me.

Fuel...there exist a lot of possibilities...from contaminated fuel to plugged injectors to improper use of your fuel controls...throttle (which is really an air control, in many installations...not a fuel control), mixture, the fuel selector, primer, etc.

If the engine isn't starting, something isn't right, be it a mechanical discrepancy (as alluded to by IO540), a fuel discrepancy, an air discrepancy, or a spark discrepancy. The mechanical you can't immediately address, but you control when spark is introduced, the amount and placement of fuel, and the airflow.

Simple solutions are to go to the extreme. If you suspect not enough airflow, an open throttle will provide the maximum. This also presents some hazard. If you're operating carbureted, it also rejects the idle throttle jet...no way to get idle fuel flow when the throttle is open, and no way to get adequate main jet fuel flow without adequate flow through the carburetor venturi...so simply opening the throttle without a means of providing additional fuel from another source...the accelerator pump is an often-abused method. The primer is another source. The open throttle does, however, provide the maximum amount of cooling airflow to be drawn through the combustion chamber prior to the introduction of fuel. It's also an excellent way to get a backfire or an afterfire when starting with fuel being introduced, so use caution. A backfire can dislodge your induction or cause an induction or carburetor fire, whereas an afterfire can damage your exhaust or cause an exhaust stack fire.

Additional prime may also help the problem, but too much can contribute to a fire, if not used judiciously. The introduction of prime while cranking may be a help, as it presupposes an increased airflow with the partially open throttle. there are two ways to start with respect to airflow and fuel flow; one is on the mixture, the other is on the throttle. One means with the mixture preset, and advancing the throttle until the proper mixture is reached (such as starting on a flooded engine; the present mixture to rich provides ready fuel flow, and advancing the throttle gradually slowly admits more and more air until the engine fires). The other method is starting on the mixture, with the throttle preset, the mixture at cutoff, and slowly advancing the mixture until the engine fires. Both methods may be done with or without a flooded engine, but can be used to take advantage of a slightly flooded situation.

Applying additional fuel, or flooding prior to cranking means that fuel is present prior to the spark. This is a generally undesireable condition; spark should usually be present prior to advancing the throttle or providing something in the engine to burn.

Applying primer to a hot engine isn't necessarily a bad thing, though it's typically thought of as a cold engine tool. It's not. It's there to be used as necessary.

Think through the firing process before arbitrarily trying a random starting technique. Your engine will have prescribed procedures for starting under varying conditions, but if these aren't working, reason out why it doesn't appear to be starting, and then address each of the possibilities; fuel, air, and spark.

[Pilot DAR]

While you're busy thinking about how to get it running, because you really want to be in the sky, consider one other important cost saving measure:

Starter motors are NOT continuous duty designs. Though a pilot is rarely reading limitations on starter motors, they do exist. They usually read like this (going from memory of my C310 days, where the pilot's operating handbook did spell it out):

Crank for a maximum of 30 seconds, wait a minute, crank for 30 more seconds, wait 5 minutes, crank for 30 more seconds, wait 30 minutes. The pilot's operating does not tell you to give up after that, and go for an expesive airport lunch, but that's what you should do, because it will still be a lot cheaper than the melted starter motor you're going to create, if you keep cranking.

30 seconds goes by pretty quickly when you're frustrated doing a troublesome hot start. That's one reason that aircraft batteries are not so big, hopefully you'll run the battery flat before you melt (and I use the word literally) the armature in the starter motor, and it will get a chance to cool down by the time you get a boost arranged!

Pilot DAR

[SNS3Guppy]

I've watched pilots melt the terminals off batteries by too much cranking on a hot engine. I saw one catch fire and melt during excessive cranking in a Cessna 207, once. We first saw it when smoke was coming from the battery compartment beneath the nose baggage floor.

[jxk]

I've had quick look at various check-lists (POHs) for the Archer and most them seem to say 'Prime as required' - not very helpful! So why is a hot engine difficult to start? This is probably due to a vapour lock; once had a Renault car that suffered this problem. The Renault fix was to allow the cooling fan to run on after the car engine was turned off thus cooling the system down; the fuel line ran over the top engine. You can disregard the impulse mag selection because its not selectable - just turn the key. Another thing I've tried is to fully open the throttle and crank until the engine until it fires and then quickly retard the throttle.
There was a theory with fuel injected engines that you could close the throttle and run the electric fuel pump, this would pump fuel through the system, the unused fuel being returned to the fuel tank. The idea being to cool the fuel system down and eliminate the vapour locks. I only mention this as this indicates again that the problem seems to be with the dreaded vapour lock.
So a Black Art.

[RTN11]

aircraft engines can always be tempremental to start. As has been said above, the starting system is nothing like car starters which we are all used to starting 1st time with no problems.

At my school, there's a arrow that is a real bugger to get going. It seems that only one instructor has the touch sometimes. I've seen other experienced instructors trying for up to 3 hours (trying, then giving it a rest and trying again) with no sucess, then this guy goes out and starts it 1st time.

Sometimes its just knowing what your specific aircraft needs to get started. treat her like a lady!

[IO540]

I come back to what I said earlier - when they make these planes in the factory, they all start! If they didn't they wouldn't send them out. So what has gone wrong in the years since?

It's got to be some problem in the way the carb (or fuel injection) has been adjusted.

A sort of related example: my engine used to always shudder on shutdown. When it went to the USA recently (Lyco crank swap) they said it shouldn't do that; it wrong and is a fault in the fuel servo not fully closing off the fuel flow when mixture is on idle. They lapped the valve and now it's a lot better. Yet practically all UK pilots would have simply accepted it as it was.

[RTN11]

i flew a PA-38, where on shutdown when you pull the mixture the engine carried on for a good 30 seconds before shuddering to a very noisy halt. I queried this with the flying school, and they just said it had been that way as long as they had it, and not to worry.

I never flew that particular aircraft again, but i'm guessing it still suffers the same problems.

[dwj]

I find that I need to give my continental O-300 one shot of primer if it has been sitting for 15 minutes - if I don't do that, it won't start.

Normal shutdown procedure for lycoming and continental engines is to set the mixture to idle cut-off. Therefore when you start there will be no fuel in the carb and you'll need to keep cranking the engine until you suck the fuel back into the system. Using the primer puts the fuel directly into the cylinders, so when you crank it (hot or cold) it should start immediately without having to drain your battery with endless cranking. As long as you don't overdo it there is no chance of backfire. As another poster said - the primer is there to be used, so use it!

[Tinstaafl]

Well said, SN3. My experience over many years has been that if an engine is consistantly difficult to start (or is becoming more & more difficult to start) when using correct technique then there is a problem with it and it's time to talk to your engineers/mechanics. With detail about how, what, when, any common factors etc. so they can diagnose the problem. I can't think of any problems that haven't been able to be solved by them (eventually. Bloody intermittent problems are a curse!)

[n5296s]

I come back to what I said earlier - when they make these planes in the factory, they all start! If they didn't they wouldn't send them out.
Not sure about that. I flew a nearly-new SR22 a couple of years ago that had some kind of fancified hot-rodded engine (I think they called the plane a "Millenium Edition"). It was incredibly hard to start, which the instructors all knew about. You had to prime it exactly the right amount, and have the mixture and throttle in exactly the right position, and even once it had started, you had to nurse it for 30 seconds, gradually advancing the throttle and mixture at JUST the right speed, or it would cough and die - and refuse to start again. What a pain.

When I started flying I had a share in a (then) new 182, with injection. It was amazingly hard to start after a short shutdown, although I never actually failed. Everyone assumed the problem was vapour locks. You would try every trick in the book - mixture lean, mixture full rich, throttle open, throttle closed, no prime, lots of prime - and eventually one of them would catch its attention and it would start. Stone cold, it started first time every time.

My TR182, which is a carb engine, starts like a dream, whether hot or cold.

n5296s

[Flash0710]

I flew an archer III last yr and it was a bitch when it was hot......

After a few days i found the knack was to have....

Mixture rich

Throttle ICO

Crank and as soon as she fired throttle fully forward then reduced back to 12....

It was specific to that particular aeroplane but. if yr running out of ideas it may work for you...


Not an expert disclaimer....


luv

xxx
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