Priming engine

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evapilotaz

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Are you suppose to prime the engine every time before startup or do you prime only when the engine is cold? Here what happened to me recently. I landed the airplane and it sat for 30 minutes. I attempted to restart and it wouldn't start until I gave it 3 prime pumps.
 
Depends on the plane, my personal plane, under 30 min I don't prime, otherwise one shot and it'll turn over in a blade or two, if its REALLY cold well my plane is not happy when its really cold, thus the heaters.
 
evapilotaz said:
Are you suppose to prime the engine every time before startup or do you prime only when the engine is cold? Here what happened to me recently. I landed the airplane and it sat for 30 minutes. I attempted to restart and it wouldn't start until I gave it 3 prime pumps.
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What does the POH say?
 
...also depends on how good your starter is. :)

We put a new Sky-Tec in our Cherokee, new battery and solenoids and it is like a new plane. Even cold (well, as cold as it gets in central Texas) all she needs is 4 shots and she'll turn over in 2-3 blades. If she's hot, like after a quick stop at the pumps, there's no need to prime at all...she'll turn over on the first blade.

But like others have said, best to read your POH. That said, every plane I've ever been in has it's quirks that you just have to learn. There's also big differences, especially with hot starts, between carburated engines and fuel injected engines so make sure if you're reading stuff on the internet that you distinguish between the two. I know some people don't prime at all using my same engine - they just cycle the mixture control a few times and fire it up.
 
My AA5 requires prime every start. My AA1A needed prime only for cold stsrts. Whatever works.
 
evapilotaz said:
Are you suppose[d] to prime the engine every time before startup or do you prime only when the engine is cold?
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For a 172M, I use 2-3 squirts of primer when the engine is hot.
 
jordane93 said:
When in doubt, just look at the POH. It will give you the proper procedures for a hot start, cold engine, flooded engine, etc.
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That is a very generous statement to the people who wrote the POH.

What plane, what engine?
 
If your 172M is powered by a Lycoming O-320E2D (came stock with this engine) . I've flown an E2D powered 177 for years and here are my thoughts;

(1) The E2D in in many Cessnas came with ONE primer nozzle installed in 1 out of the 4 cylinders, so the manual primer is only priming the #4 cylinder (or is it #2?). Doesn't seem optimal does it? It's NOT. IF equipped better it will have a maximum of 3 primer nozzles, which yield much quicker starts.

(2) The ED2 is likely equipped with Slick magnetos, and only 1 of them is firing when you crank the engine with starter, meaning only 4 of the 8 spark plugs fire while the ignition switch is held in the "START" position, again, not optimal. If that magneto is weak it may be nearly impossible to get the engine started.


(3) Slick magnetos are known for a higher "coming in speed", meaning where it fires all spark plugs continuously without skip. IRRC the coming in speed is ~200 RPM for Slicks vs ~150 RPM for Bendix magnetos. So Slicks aren't ideal for easy starting engines.


(4) Back to the "firing 4/8 plugs during start", if there is fouling or contamination of one or more of those plugs its difficult, especially if the plug located with the manual primer nozzle is shorted, priming won't help.

(5) The carburetor is equipped with an accelerator pump which literally squirts fuel into the intake manifold when you advance the throttle quickly. This in effect can "prime" all 4 cylinders. Since it increases the risk of carburetor fires by loading the intake manifold and everything else up with gas, it's advised to only pump the throttle DURING engine cranking. Some people will flame me for this one but it can save a lot of battery and starter abuse. Leaving the throttle at higher settings between 1 or 2 pumps will help pull more fresh air saturated with fuel into the cylinders. As she starts to pop, slowly pull the throttle to near idle and it will go.

I get perfect starts and sometimes crappy starts. I know how it all works, flown it for years, converted to dual impluses so all 8 plugs fire during cranking, new carburetor, new mags, new harness, and new plugs, it still isn't as easy to start as many other aircraft, but sure runs good.


Hopefully that gives you some insight as to what is occurring when you start. Don't forget that fuel has to vaporize. With the E2D two shots of primer with a warm engine, wait a few seconds then crank. Pushing the primer harder will get a finer mist of fuel from the primer nozzle(s) for better vaporization than slow & easy.
 
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timwinters said:
A good place to start certainly but there can be quite a difference from one O-320 or O-360 to the next...or any other engine.
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Indeed. A friends 177B (Lycoming O-360A1F6D) with a D2000 Bendix mag starts about as easy as a brand new Japanese motorcycle. Note: it is equipped with the 3 cylinder manual primer.
 
Thanks the replies. Its a 1978 Cessna 172N 160 Horsepower.

I will try to find a POH online before tomorrow.

What had me nervous as well is when the airplane wouldn't start, the battery started sounding a little weak. I must have cranked it too much. I was also at a remote airport with no one around. I gave it 3 primes and said "Please god let it Start" and it did. Lesson learned.
 
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This is kind of like a 'how to lean' topic.

My plan usually is try it without prime and if it doesn't start give it a few primes and see.
 
There is A LOT of variation even between identical models. It depends on a lot of things, not the least of which are engine condition, plug fouling, starting system condition, ignition system condition, and ambient temperature.

Example: CAP has a nice 182R that starts with two strokes cold, nothing hot, nearly instantly. A civilian 182P at the same field needs three strokes cold, and starts OK. Another civilian 182Q at a field with higher humidity (much closer to the ocean) requires three cold, two hot and takes some effort to crank. These are all carbureted.

These are all recent summer results.

The only way you're going to really know is to ask that particular airplane's owner. You'll get some ROUGH rules of thumb, like 177 engines are a royal PITA to start hot -- basically, run the boost pump mixture rich until the flow is steady, then cut the mixture off, open the throttle between half and full and attempt a flooded start. Or wait 30 minutes and skip the priming.
 
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evapilotaz said:
I guess I should review it for the C172.
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Which engine -- Continental O-300, Lycoming O-320, or Lycoming IO-360? In any event, read your POH, and remember that oil temp is the best indicator of what type start (cold, warm, or hot) to use.
 
Ron Levy said:
Which engine -- Continental O-300, Lycoming O-320, or Lycoming IO-360?
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:thumbsup:
 
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