orionflt Posted March 23, 2015 Report Posted March 23, 2015 Dev, The C model in the cold with out preheat can be tricky to start. I found that giving it 3-4 pumps then with everything shut down and the mags off pull the prop thru so you cycle thru all 4 cylinders. then I hop back in and fire everything back up. It may not stay running on the first attempt to start but if you pump the throttle another 3 times and try again it will usually stay running. my rule of thumb is if the cylinder temp is below 40 (temps below 40 the night before) expect trouble starting if you do not preheat, the colder the temp the harder it will be to start. what is happening is the cold cylinder walls are condensing the fuel keeping you from getting the optimum fuel air mix you need for starting. by leaving the fuel in the cylinder longer before attempting the start gives it more time to vaporize. just remember when you are doing this not to over crack your starter ( follow the duty cycle limits of the starter) and know that when you engine is cold sometimes it just wont start with out preheating it first, Brian 2 Quote
Oscar Avalle Posted March 23, 2015 Report Posted March 23, 2015 Mine fires right up... Boost pump on and when pressure is built up, I shut it off. Then two pumps of the throttle. I make sure is see the fuel pressure drop with each pump. Crack the throttle a 1/4 inch had the fires right up. Then I lean it pretty aggressively. I use the same procedure. Quote
Andy95W Posted March 23, 2015 Report Posted March 23, 2015 This weekend it was a bit warmer- got down to 35 at night and was in the mid 40s when I got to the field. I hadn't put the heater on, and I was wondering how it would go. Not too well, it turns out. I tried same process as above but used 5 pumps of the throttle, cranked for 15 sec- nothing. Added four more pumps. Tried again- nothing. Sat on my hands for 30 sec, tried again- nothing. Sat on my hands for two minutes, used boost pump again, 7 pumps, cranked 15 seconds- nothing. Got out of plane, made sure nose gear not sitting in a puddle of fuel, tried flooded procedure- nothing. Grew despondent, considered giving up and taking up gardening instead. Added 2-3 pumps again, cranked 15 seconds- seems to sputter a bit but won't start. Sat on my hands again for 2 full minutes, no pumps, and it started instantly. Good Lord, that's a lot of pumping! For me, down to 30°, 2 pumps on the throttle and it starts. One pump if the temperature is above 70°. Below 30° I pre-heat. The priming method for our O-360's is pretty archaic and only utilizes the accelerator pump from the carburetor- which means it squirts raw fuel straight up into the intake manifold where it splashes and falls straight back down, through the carburetor venturi, and into the air box under the carb. More pumping = more fuel in the airbox = more fuel running onto the nose wheel (if the drain hose is actually installed). If the drain hose isn't installed = more chance of a fire. In warm weather, the fuel vaporizes and the vapor is pulled into the cylinders on the intake stroke. In cold weather, very little atomization and very little fuel goes into the cylinders. One way to help this process is to crank the engine WHILE pumping the throttle 2-3 times. This will at least ensure fuel is getting into the cylinders on the intake stroke, but can lead to a flooded engine if excessive. 1 Quote
DXB Posted March 23, 2015 Report Posted March 23, 2015 Dev, The C model in the cold with out preheat can be tricky to start. I found that giving it 3-4 pumps then with everything shut down and the mags off pull the prop thru so you cycle thru all 4 cylinders. then I hop back in and fire everything back up. It may not stay running on the first attempt to start but if you pump the throttle another 3 times and try again it will usually stay running. my rule of thumb is if the cylinder temp is below 40 (temps below 40 the night before) expect trouble starting if you do not preheat, the colder the temp the harder it will be to start. what is happening is the cold cylinder walls are condensing the fuel keeping you from getting the optimum fuel air mix you need for starting. by leaving the fuel in the cylinder longer before attempting the start gives it more time to vaporize. just remember when you are doing this not to over crack your starter ( follow the duty cycle limits of the starter) and know that when you engine is cold sometimes it just wont start with out preheating it first, Brian Thanks Brian- I will try the trick with pulling the prop through next time temps are marginal. But wouldn't turning with the starter the first time accomplish the same thing to distribute fuel? The waiting to vaporize and trying again should work. I guess the real answer is preheat, but it's inevitable at some point that I'll get caught out somewhere with temps in 30s and no preheat available, so I might as well figure this out now. Quote
orionflt Posted March 23, 2015 Report Posted March 23, 2015 when you crank with the starter you cycle thru the cylinders too fast and the fuel doesn't have time to vaporize, pulling thru by hand gives it the time it needs. I have tried pumping the throttle 3-4 times then spin the prop 3-4 turns with the starter, then waiting a minute but I have had less success with that and usually end up flooding the engine trying to get the right fuel air mix. Brian Quote
Hank Posted March 23, 2015 Report Posted March 23, 2015 I generally pull out of the hangar then pull the propeller through two revolutions. Run the boost pump until fuel pressure stabilizes, then turn it off. Pump the throttle 3-5 times, watching the fuel pressure decrease. Wind & set the clock, put on headset, pull out checklist and verify everything, mixture rich and turn the key. If it doesn't fire after several seconds, pump the throttle several times while continuing to crank. It may take a second try. I do this even with preheat, since the fuel is still cold. Preheat warms the engine, but cold fuel still vaporizes slowly. Quote
Alhall Posted March 25, 2015 Report Posted March 25, 2015 When it's in the 20's I use a small preheater I made from a ceramic heater and aluminum dryer hose. Stick the hose in the cowl flap for 10 or 15 minutes. Works good. Al Quote
par Posted March 26, 2015 Report Posted March 26, 2015 I need to revive this thread so I can figure out how to cold start. All 15 hrs in my 'C have been in the northeast winter so far, but I've always had a space heater blowing into the cowl the night before. If I do this, it starts instantly on the coldest day no matter what procedure I use (typically mixture rich, boost pump on briefly to get pressure in green arc, 3-4 pumps throttle and then crack open, crank). This weekend it was a bit warmer- got down to 35 at night and was in the mid 40s when I got to the field. I hadn't put the heater on, and I was wondering how it would go. Not too well, it turns out. I tried same process as above but used 5 pumps of the throttle, cranked for 15 sec- nothing. Added four more pumps. Tried again- nothing. Sat on my hands for 30 sec, tried again- nothing. Sat on my hands for two minutes, used boost pump again, 7 pumps, cranked 15 seconds- nothing. Got out of plane, made sure nose gear not sitting in a puddle of fuel, tried flooded procedure- nothing. Grew despondent, considered giving up and taking up gardening instead. Added 2-3 pumps again, cranked 15 seconds- seems to sputter a bit but won't start. Sat on my hands again for 2 full minutes, no pumps, and it started instantly. It's clear I don't know what I'm doing after the standard procedure won't work, and it was dumb luck that I ultimately got it started. Next time I suspect I'll go up in flames or cause other damage. What do other folks do when it doesn't start cold after the first couple of tries? Is there any way to know if it is too lean and I should pump more, or if it is flooded (other than the smell of fuel and seeing it on the nose gear)? I had a very similar experience and you can see a lengthy discussion about it on here if you desire. Long story short, I had multiple starting attempts on a cold engine (25 degrees) until the engine eventually backfired and set the pooling fuel in the air box on fire. Since then, I kept 2 light bulbs in the cowling if the weather was cold and even after the coldest night, the oil temp was a nice 40-50 degrees. Also, I hand turn the prop at least 3 or 4 times before attempting a cold start these days and I have not had a single issue since that day. The procedure I use is similar to what everyone else has stated above: master on, pump on, pump 3 times, pump off, wait 30 seconds, crank. Like I said, no issue at all. Quote
DXB Posted March 30, 2015 Report Posted March 30, 2015 Dev, The C model in the cold with out preheat can be tricky to start. I found that giving it 3-4 pumps then with everything shut down and the mags off pull the prop thru so you cycle thru all 4 cylinders. then I hop back in and fire everything back up. It may not stay running on the first attempt to start but if you pump the throttle another 3 times and try again it will usually stay running. my rule of thumb is if the cylinder temp is below 40 (temps below 40 the night before) expect trouble starting if you do not preheat, the colder the temp the harder it will be to start. what is happening is the cold cylinder walls are condensing the fuel keeping you from getting the optimum fuel air mix you need for starting. by leaving the fuel in the cylinder longer before attempting the start gives it more time to vaporize. just remember when you are doing this not to over crack your starter ( follow the duty cycle limits of the starter) and know that when you engine is cold sometimes it just wont start with out preheating it first, Brian I tried this trick this weekend. Definitely seems to help! Thanks again. 2 Quote
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