Cold Wx Start

[dmccormack]

This morning I planned an early flight.

Wx was 20 F and clear with light southerly winds.

The Airplane is a Cessna 205 (IO-470) stored in a hangar with a space heater in the cabin set to 65 F and a new Aerotherm Engine heater with inlet and outlet and temperature setting. It was set to 80. The heavy insulated blanket over the cowl was nice an toasty, and the oil flowed freely and all fuel drians (there are 5) flowed freely with no water (as usual).

After clearing the snow and ice from in front of the hangar, I pulled it out solo (no easy feat -- this is a heavy bird and there was a bump of ice to push over).

I clsoed up the hangar, double-checked all a/c doors, and got in.

The engine heater had been off for maybe 5 minutes.

I tried to start using normal POH start technique (Mixture rich, throttle 1/2" in, fuel pump on low).

It turned over fine (as it would on a sumemr day) but never caught.

I waited and tried a few more times (including mixture lean and no fuel pump) and nothing -- not even a hint of firing.

This is the first time I've tried starting this airplane in these conditions (extensive preheat -- days -- and cold ambient temperatires), and this is the first time it hasn't started.

All otehr indications were good -- this airplane flew last about a month ago with no start problems (the pre-heater wasn't used -- ambinet temps were mid-40s then).

Can the change from toasty warm 80 degrees to 20 degrees cause this behavior?

I'm stumped...

 

[Rob Schaffer]

I don't have much experience, but the one thing I learned on the Cessna 172SP models with fuel injection was that it is often helpfull to prime with the fuel pump like normal, turn off. Then set your mixture and throttle for starting and when you first kick the starter, turn on the fuel pump, and turn off once she starts and is running smooth. In the 172SP, the fuel pump switch is right beside the key, so I can turn it on and off using my thumb of my left hand, so I still have my right hand on the throttle and mixture.

I learned this from the Maintenace guy at my FBO, after I was pulled out of the heated hangar where the rentals were stored overnight. It was comfy in there, so much so I took my jacket off after I completed the preflight and waited for other renters to complete. Outside, it was barely 20*, with it being in the upper teens overnight.

I don't have experience with preheat and it's affects other than this,.. but maybe something to share since it wasn't in the POH either of the 172SP.

 

[Trapper John]

I tried to start using normal POH start technique (Mixture rich, throttle 1/2" in, fuel pump on low).

It turned over fine (as it would on a sumemr day) but never caught.

I waited and tried a few more times (including mixture lean and no fuel pump) and nothing -- not even a hint of firing.

I'm stumped...

Maybe a coincidental ignition system failure like an impulse coupling?


Trapper John

 

[bbchien]

Dan, I used to own one of these. Under you conditions I would do the flooded start technique (Run the fuel pump, mixture wide open, ten seconds), then crank with the mixture at idle cutoff and throttle full open....

 

[dmccormack]

I don't have much experience, but the one thing I learned on the Cessna 172SP models with fuel injection was that it is often helpfull to prime with the fuel pump like normal, turn off. Then set your mixture and throttle for starting and when you first kick the starter, turn on the fuel pump, and turn off once she starts and is running smooth. In the 172SP, the fuel pump switch is right beside the key, so I can turn it on and off using my thumb of my left hand, so I still have my right hand on the throttle and mixture.

I learned this from the Maintenace guy at my FBO, after I was pulled out of the heated hangar where the rentals were stored overnight. It was comfy in there, so much so I took my jacket off after I completed the preflight and waited for other renters to complete. Outside, it was barely 20*, with it being in the upper teens overnight.

Interesting, Rob.

Makes me wonder if vapor lock was the issue?

 

[dmccormack]

Dan, I used to own one of these. Under you conditions I would do the flooded start technique (Run the fuel pump, mixture wide open, ten seconds), then crank with the mixture at idle cutoff and throttle full open....

Bruce -- flooded start technique right at the begining? Or after it won't start?

 

[gismo]

Can the change from toasty warm 80 degrees to 20 degrees cause this behavior

Not directly no. I'll bet your CHTs and oil temp were still within 10 degrees of what they were in the hangar. Something else must be causing the failure to start. Either your mixture is too lean, something is plugging the fuel (ice in a line?) or you aren't getting any spark for some reason.

From your description, I'd guess that you needed to prime. The combination of cold fuel and cold air typically requires a lot more priming than when the temps are more moderate. My normal cold weather starting procedure for the IO-470Ls on my Baron involves full throttle, full rich, run the boost pump on high until I see at least 10 gph fuel flow. Then pump off, throttle almost closed (your 1/2" is a bit much) and crank.

 

[dmccormack]

Not directly no. I'll bet your CHTs and oil temp were still within 10 degrees of what they were in the hangar. Something else must be causing the failure to start. Either your mixture is too lean, something is plugging the fuel (ice in a line?) or you aren't getting any spark for some reason.

From your description, I'd guess that you needed to prime. The combination of cold fuel and cold air typically requires a lot more priming than when the temps are more moderate. My normal cold weather starting procedure for the IO-470Ls on my Baron involves full throttle, full rich, run the boost pump on high until I see at least 10 gph fuel flow. Then pump off, throttle almost closed (your 1/2" is a bit much) and crank.

Hmmm... I didn't try running the boost pump on high.

 

[Ted]

Remember that the amount of fuel you need has more to do with the air density (i.e. temperature) than CHT. Cold cylinders make combustion more difficult and do require more fuel, but the air temperature is the big one here.

I don't have any experience starting injected Continentals, but on the injected Lycomings I fly I would have used the cold start technique, and put more fuel in. On the Mooney, for example (IO-360-A1A) I would have all knobs forward, boost pump on for probably 5-6 seconds, mixture to idle cut-off (throttle still full open), crank and as soon as it catches mixture rich and pull back the throttle.

The one time I had difficulty starting on a cold day it was -12F out. The engine had a pre-heat (but only about 2-3 hours of one with a blanket over the engine, and in an unheated hangar). I primed it and it wouldn't catch. On the 5th try (I was convinced I'd frosted my plugs by then) I had primed it even more, left all the knobs forward and as soon as it coughed hit the boost pump and it caught. Once it caught, it was fine.

When the intake air temps are cold, starting becomes more difficult and you may have to do some more work to get them to start.

 

[rainsux]

> Then set your mixture and throttle for starting and when you first kick the starter,
> turn on the fuel pump, and turn off once she starts

No other option for the 205. The start/low position of the fuel pump only pumps
when the ignition key is in the the Start position.

Dan,

I have a 205. Use the same procedure as you ... no problem even when the temp
is in the single digits.

 

[Dave2]

If it doesn't even pop, my gut feeling is that the fuel air ratio was too lean.

 

[DGlaeser]

Sounds to me like the plugs got frosted. When you took the warm engine out in the cold, the engine cools quickly, and the warm, moist air in the cylinders cools and literally forms frost on the plugs - shorting them out. If that happens again, put the engine heater back on for a few minutes and try again. Cold weather sucks (I live in Michigan

 

[bbchien]

Bruce -- flooded start technique right at the begining? Or after it won't start?

Right at the beginning. You don't have many moments until the plugs frost. Run that pump, flood that puppy, mix to idle cutoff, crank throttle wide open.

30 or so compression cycles and the moisture in the intake is starting to condense....

 

[kgruber]

You have to prime it with the fuel pump on hi. Run the fuel flow up to about 20 and back down with the throttle.

Now start it without any fuel pump.

Note that you are REQUIRED to run the fuel pump up on high before start. Otherwise you'd never know if it wasn't working.

You should NEVER have to start a cold big block IO-Continental using the flooded start procedure.

 

[gismo]

You have to prime it with the fuel pump on hi. Run the fuel flow up to about 20 and back down with the throttle.

Now start it without any fuel pump.

Note that you are REQUIRED to run the fuel pump up on high before start. Otherwise you'd never know if it wasn't working.

You should NEVER have to start a cold big block IO-Continental using the flooded start procedure.

If the engine is really cold (cold enough that you ought to preheat) the fuel doesn't vaporize very well and liquid fuel just won't ignite in the cylinders. Running hi boost with throttle and mixture full forward does a much better job of atomizing the fuel dumped into the intake manifold than any other combination. Therefore, a brief prime in that condition works better than a prolonged prime delivering the same total volume of fuel with the flow restricted by any combination of low boost, less than full rich and partially closed throttle. Priming while cranking also works (same condition: full throttle, mixture full rich, hi boost) but in my airplane it takes three hands because you have to pull the throttle back very quickly to avoid damaging high revs at startup.