C152 Hot Start tips

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avcraig
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C152 Hot Start tips

Post by avcraig »

Hey all,

Does anybody have any tips on hot starting the C152? There's been a few dual flights, and solo flights, when the engine would have the hardest time starting when it was just flown 20 minutes prior, or been sitting in the scorching heat all day.

I was taught to use no priming, Mixture ICO, and just a little bit of throttle when starting. Once the engine starts, mixture rich and about 1700 rpm for about half a minute or so, then back to idle 1000 rpm. This always seemed to work with my instructor but never when I'm solo. Pumping the throttle a few times has also worked sometimes however according to my instructor that is the very absolute last resort since many fires can happen that way.

Do any of you have any tips on hot starting the C152? Yes, I have read the POH but none of that seems to work for me the majority of the time anyways. I've been told that these 152's are notorious for their hot starts, which is another reason why I've been thinking of switching over to the 172 since I'm told they don't have these problems.

Thanks.
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tired of the ground
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Re: C152 Hot Start tips

Post by tired of the ground »

Don't pump the throttle, prime, no pumping. The way we always got tough engines to go was to prime quite a bit then throttle full open and mixture ICO as you crank. As soon as it catches throttle to idle (1000rpm) and mixture full rich. It seems like you need three hands but it doesn't happen as fast as you might think.

Try it with the instructor on board to supervise first.

You shouldn't be running an engine at 1700 rpm when you first start it. It's bad for everything. Warm it up at 1000rpm, then when you taxi out for a runup you have some heat in it and you're probably ready for a runup.
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avcraig
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Re: C152 Hot Start tips

Post by avcraig »

tired of the ground wrote: Fri Sep 07, 2018 6:05 pm Don't pump the throttle, prime, no pumping. The way we always got tough engines to go was to prime quite a bit then throttle full open and mixture ICO as you crank. As soon as it catches throttle to idle (1000rpm) and mixture full rich. It seems like you need three hands but it doesn't happen as fast as you might think.

Try it with the instructor on board to supervise first.

You shouldn't be running an engine at 1700 rpm when you first start it. It's bad for everything. Warm it up at 1000rpm, then when you taxi out for a runup you have some heat in it and you're probably ready for a runup.
I see, so by "prime quite a bit" do you mean 3 pumps or so (what is usually used in the winter)? Also, by "catches" do you mean when the engine starts or when it's just on the tip of starting but still not quite there? Seems like a lot to do at once when the engine starts but I'm sure I'll manage.
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tired of the ground
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Re: C152 Hot Start tips

Post by tired of the ground »

Try 2 pumps and if that doesn't work, try 3.

"catches" means lights off, sort of almost running. The fuel you've put into the carb will run the engine for about 1-2 seconds with the mixture at ICO. You have time.

Working at starting an engine isn't a reason to fly a more expensive airplane. If you're having trouble starting it, get help. If my tips don't help, get your instructor to walk you through it some more. If that doesn't work, go talk to maintenance. If you come in with some humility they will be happy to walk you through it.

I promise, you'll figure it out.
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7ECA
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Re: C152 Hot Start tips

Post by 7ECA »

avcraig wrote: Fri Sep 07, 2018 5:49 pmI've been told that these 152's are notorious for their hot starts, which is another reason why I've been thinking of switching over to the 172 since I'm told they don't have these problems.
These little four bangers are far from complex - and I've yet to see or hear anyone describe the carb'd Lycoming on a buck-fifty-two as "notorious" for difficult hot starts.

Now, what's really entertaining (at least for bastards like myself) is watching students kill the battery on fuel injected 172s. They're a bit finicky the first time you try a hot start - but just follow the POH and she'll go.
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photofly
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Re: C152 Hot Start tips

Post by photofly »

Does anybody have any tips on hot starting the C152?
There's no such thing as "the" C152. Every 152 in existence is at least 30 years old, and is probably using at least its third engine. Each magneto has been repaired or overhauled or replaced ten times during the lifetime of the aircraft, and so has the carburettor. All of those things, along with the state of the plugs, the ignition lead insulation, the magneto timing, the setup of the impulse coupling and about a dozen other factors can affect the starting of the engine.

I've flown a C152 that starts first blade every time, hot or cold, and a bunch of C150's that between them include some easy starts, and some that for a period become really difficult. It's really a maintenance issue, but not always one that it's easy to get an FTU interested in fixing, unfortunately.
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PilotDAR
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Re: C152 Hot Start tips

Post by PilotDAR »

Do not run any piston engine at 1700 upon starting! Oil really has not circulated much. It's much better for the engine to idle as oil pressure builds, then once oil pressure is indicating, open the throttle only as required. The engine probably won't idle smoothly with the throttle fully closed, but a quarter inch or so open should be all that's needed to idle nicely ate 800 to 1000 RPM. So, only for a flooded engine, would opening the throttle more than that for staring be a good idea.

If a carburetted engine is "hot", it might not need priming at all, first try a brief start with no prime, and see what it does. Five revolutions of the engine (ten propeller blades passing for a 152) should be enough, if it catches, keep cranking.

The flight manual does state that you can clear a flooded engine by cranking with the throttle open, and the mixture at ICO. And it says to repeat the starting procedure after doing that. There are engines whose starting procedure does include actually starting with the mixture at ICO, and enriching as the engine begins to run, the Lycoming 235 in a 152 is not one of these engines. The Amplified Procedures for starting engine in the flight manual is worth a re read, it does explain all this, and is the authoritative reference for "tips".

Though most flight manuals do not state starter motor limitations (the Cessna 310 I used to fly did), it is potentially harmful for most starter motors to exceed the following starting cycle: Crank for 30 seconds, stop for 30 seconds, crank for 30 seconds, stop for 5 minutes, crank for 30 seconds, stop for 30 minutes. A cycle of 5 to 10 seconds should be enough to get a cooperative engine running, so 30 seconds gives you a margin for success. Starter motors are poorly cooled, and can literally be melted inside by prolonged cranking (I've taken them apart following failure when I worked at the engine shop). This seems to be little considered for instruction and limitation in flight manuals of piston aircraft, as it's not really a "safety of flight" issue, but it's still expensive for someone to have to replace a starter, and makes the plane unavailable for use.
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CpnCrunch
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Re: C152 Hot Start tips

Post by CpnCrunch »

I think the problem is that you've confused the 152's engine for something that is fuel injected! You don't start a carburreted lycoming with mixture at ICO, except perhaps in the case of a flooded engine as pointed out above.
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Big Pistons Forever
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Re: C152 Hot Start tips

Post by Big Pistons Forever »

After 1978 Cessna modified the primer system on the C 152 to prime all cylinders, rather then just one. This mod made the engine significantly easier to start.
The hot start method you describe requires you to deliberately flood the engine. The idea is you start with a known engine condition, flooded with excess fuel. The mixture ICO will ensure no new fuel is added and as the engine cranks the excess fuel will be used up until the correct fuel air mixture is reached at which point the engine will start and you advance the mixture to keep it running.

If you have an old style primer system you are probably not getting enough fuel to reach the flooded stage so the engine won't ever start as it will never have enough gas.

However that been said you never specified if it is every C 152 you are having difficulty or just one. If it is just one airplane then the problem is that airplane is broken and needs to be fixed as there are numerous issues that can cause hard starting.

If it is every C 152 then your technique is the problem. Personally I do what Pilot DAR does, start with no prime and see what happens. If no joy after 5 revolutions I found a half shot of prime works every time. The initial cranking will have cleared the engine and the little bit of prime will get her going almost immediately. If that doesn't work then go for the flooded start procedure.
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CpnCrunch
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Re: C152 Hot Start tips

Post by CpnCrunch »

I have noticed something similar on my 172 (O-360). Engine cold it always starts immediately with 2 shots of prime, but if the engine was shut down, say 15-60 mins ago and it's a hot day, it won't start with 0, 1 or 2 shots. It seems to require a third shot of primer to start (and then it starts immediately).

I wouldn't say it's hard to start. It starts perfectly if you prime it the right amount. But if you try to start it with no priming, you'll be cranking a long time!

I assume the fuel in the fuel lines is just vaporising due to the heat, and more priming is just required to get fuel into the engine.

Anyway, I think the solution is just to learn how much priming your engine needs in various situations. Priming is always preferable to pumping the throttle.
I've flown a C152 that starts first blade every time, hot or cold, and a bunch of C150's that between them include some easy starts, and some that for a period become really difficult. It's really a maintenance issue, but not always one that it's easy to get an FTU interested in fixing, unfortunately.
We're not talking about hot starts per se. The problem generally doesn't happen if you shut down and restart immediately, only if the engine is left shut down for a while. I can't really see how it could be a maintenance issue if it starts immediately with one extra shot of primer.

It does seem to be a somewhat common issue:

https://www.pilotsofamerica.com/communi ... rts.35923/

And people have weird and wonderful hacks, this one somewhat similar to the technique used in fuel injected engines:
I have an O320-D3G that is carburated.

I find the easiest hot start is no prime, throttle full open, mix at idle cut off and then crank. The second it starts to catch pull the trottle and push the mixture to full rich.
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PilotDAR
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Re: C152 Hot Start tips

Post by PilotDAR »

check that your idle mixture is set rich enough. If it idles less well, this could be a factor. My Lycoming O-360 seems to "adjust" it's idle mixture on its own every now and then. It'll start with prime, idles poorly, and runs perfectly once the throttle is opened - then idles poorly again on rollout and taxiing. For mine, with the side draught carb, 4 1/2 turns of the idle mixture seems about right - I'm trying to figure a way to lock wire it there, but it's a "feel, but cannot see" type arrangement.
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CpnCrunch
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Re: C152 Hot Start tips

Post by CpnCrunch »

PilotDAR wrote: Tue Jul 26, 2022 7:40 pm check that your idle mixture is set rich enough. If it idles less well, this could be a factor. My Lycoming O-360 seems to "adjust" it's idle mixture on its own every now and then. It'll start with prime, idles poorly, and runs perfectly once the throttle is opened - then idles poorly again on rollout and taxiing. For mine, with the side draught carb, 4 1/2 turns of the idle mixture seems about right - I'm trying to figure a way to lock wire it there, but it's a "feel, but cannot see" type arrangement.
I don't seem to have any problem at idle. Maybe your threads are just worn or something.
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