Cold Weather Starts

[SeaAir]

A quick question for those who live in cold areas...

At what temperature would it be a good idea to get an engine pre-heat, and how damaging is it to the engine to start it on a cold day?

(Alright, so it's two questions.)

See http://www.avweb.com/articles/preheat.html

[summitgolfer]

I'm in Alaska, where you see preheaters at and below freezing. I've started my 180 at 15*F and it fired at the very moment the battery gave out, after only two prop rotations. I guarantee a preheated engine is easier to crank. Guys with older engines aren't as fussy about preheating as guys with new engines, but preheating any engine is the right thing to do. As far as damage... I'm lucky enough not to know the answer, and hope it stays that way.

[Chapster]

It is analagous to the car you drive, particularly with respect to those car's whose engines have difficulty starting in cold weather conditions. As the temperature drops, the viscosity of the oil in the engine rises and it could become gelatinus (even with multi-viscosity oils; oil is a fluid and is affected by temperature to a certain degree). If the oil in the airplane engine can not easily be drawn out of the wet sump, through the low and high pressure screens, through the pump, into the oil filter, out pass the temp and pressure gauges, and finally into the engine, than what is adequately lubricating engine parts during the first minute from crank to when the engine begins to warm the oil and lower its' viscosity?

Also, as the temp drops, moisture in the fuel line may begin to partially freeze and block the line, or dislodge into the engine and stifle combustion. The cranking wear and tear, particularly on the starter motor, geared flywheel, the crankshaft, and the piston rings (as opposed to the actual piston which has a clearance beside the cylinder wall). At this point you quickly begin to see how damaging a cold start can be for auto and aircraft engines.

In Minnesota and other cold winter States, for example, there are outfitters that install block heaters (just coils of wire fillament) which you can plug into receptacles at certain venues around cities and keep the engine fairly warm. For aircraft, I have seen a propane heater directing hot air into the bottom of the block while the plane rested in an unheated hangar.

[Sageair]

If you have to start your engine without the benefit of preheat I have found that it really helps to pull the engine thru at least 10 to 15 times to loosen up the oil. It may very well make the difference between your battery having enough ooomph to start the engine or not as it will not have to overcome so much resistance from the thick oil. Just be sure to pull the prop thru backwards, that is opposite normal rotation so that if you have a broken or bad P-lead the engine doesn't inadvertenly start. The oil doesn't care which direction it's being moved in so long as it's being moved.

[Frodo]

You shouldn't pull a prop through backwards unless you know for sure that the vacuum pump is bi-directional. Turning a ccw pump clockwise or vise versa is a great way to break the vanes inside.

If your worried about the mags being hot, check to see if you can kill the engine momentarily before every shutdown and then assume that it will kick every time you move the prop.

[Chapster]

Also, the magnetos are simple DC motors. Moving the prop backwards won't necessarily prevent the engine from kicking on and driving the prop in the reverse...the only reason the prop spins clockwise from inside the cockpit is because the starting motor turns the engine in a certain direction and engines do work in reverse. If there is an ungrounded starter switch or loose lead on the mag, it is not necessarily recommended to pull the engine through unless it is done with absolute afety in mind and properly, i.e. always pull the prop through while falling backwards away from it to ensure, if it kicks on, that you will have a way to escape.

[sharplab]

The prop when turned in reverse will pull air in through the exhaust valves and push air through the intake valves. The engine should not have any type of fuel/air charge for combustion therefore it would be almost impossible for the engine to fire counterclockwise. It is much safer to turn your prop in reverse for safety along with moving away from the prop after rotating.

Stephen C. Sharp

[Chapster]

Ahhh tis not true an engine does not operate in reverse even with hydraulic lifters and mechanical cams. The crankshaft rotation is independent of piston movement because the pistons always move horizontally or vertically whereas the crankshaft rotates clockwise or counterclockwise. British engines and American engines do not operate in the same direction...

The magneto is a simple dc motor and will provide a negative voltage and current to the plugs which will still fire the engine if there is any fuel in the cylinder. This is why it is best to increase throttle and reduce mixture to idle so all the fuel remaining in the cylinder will burn up.

[skid]

Back to the topic, the colder it is the more carefully you should warm up the motor. A new motor is MUCH more critical than a high time one. I keep an oilpan heater plugged in on mine with a blanket over the cowling whenever the temps drops below about 50. This will keep cylinders about 60-70 on a 0 F day in an enclosed hangar. Thermostat on heater keeps oil from getting too hot in the spot the heater is glued to. The blanket will keep heat in cowling so entire motor is at 60 or more. Condensation will not form on something warmer than ambient air. This works well in an enclosed hangar, your airplane is already going downhill if you keep it outside. Tanis heaters should not be left on as they get things too hot in some areas; they are made to quickly preheat. A little common sense goes a long way. Even with preheat idle motor to let it slowly come up to operating temp. At uncontolled fields I see people idle their turbos for 5 minutes on arrival, then taxi out and take off only a minute or two after fire up. If you use a gas fired forced air preheat make sure the insides of motor get warm not just what you can feel.