You want the engine to like it’s
As the PIC you are going to be doing your best to take care of your engine. We’ll cover a few hot topics of what you should and shouldn’t do to ensure your engine runs right, as well as troubleshooting when it feels like it’s slacking a bit. We’ll cover the common topics or “problems” often encountered managing aircraft engines.
Your POH will tell you when to use Carb Heat (some airplanes want it anytime you are below a certain RPM, others want it only when you suspect Carb ice). When you use Carb heat it bypasses the regular air filter and pulls in air that is passed over the exhaust manifold to heat it before going to the Carburetor to be mixed with fuel. This warm air that is heated by the exhaust manifold is less dense than the outside air and thus produces less power, plus it enriches the mixture due to there suddenly being fewer air molecules for the same amount of fuel flowing to the engine. Another thing to be aware of is it is bypassing the air filter when you turn on carb heat, so be cautious how much you use it on the ground where there is more debris in the air than there is up high when you are flying.
You are most likely to get Carb Ice to build up in your carburetor when you have power settings less than full throttle and the outside air temperature is between 20F and 70F with high humidity.
When you get Carb Ice it will be noticed in one of two ways. With a fixed pitch propeller (one where you just control the throttle to the engine and the blades do not change their angle) you will notice a decrease in engine rpm similar to if you were just reducing power to the engine. With a constant speed propeller (one where you do control engine rpm and power separately) you will notice a decrease in manifold pressure. When you detect carb ice and turn on carb heat, you will first notice a further decrease in rpm as the hot air enters the intake and melts the ice, followed by a gradual rise in rpm.
Note: fuel injected engines cannot get carb ice since they do not have carburetors. Induction system icing is still possible with fuel injected engines, but far more rare than picking up carb ice.
High Oil Temperatures
Common causes of high oil temperature are the engine producing too much heat, or low oil level. To remedy the engine producing too much heat you could:
- lower the nose to increase airspeed and engine cooling
- reduce power to the engine
- increase rpm and decrease manifold pressure if flying a constant speed propeller aircraft
- enrich the fuel/air mixture (more fuel will actually cool the engine as not all of it will burn and make more heat, instead a good portion of the additional gas you add will carry heat away and leave the exhaust pipe as un-burnt fuel)
- open cowl flaps if installed on the aircraft
Low Oil Pressure
Commonly caused by very high oil temperatures or low oil level. Neither are good scenarios. If you can’t remedy this quick, think about landing real soon!
High CHT (cylinder head temperature)
- Climbing too steep (not enough airflow to cool engine)
- Operating with too much power
- Using lower octane gas than required
- Oil level is too low and not able to help keep the engine cool
- Mixture is set too lean (not getting enough fuel to keep combustion temperatures down)
- Reducing power
- enriching mixture
- lowering nose and increasing airspeed
- using higher octane fuel
High EGT (exhaust gas temperature)
Generally due to the mixture being too lean. Enrich the mixture, adding more fuel and helping to cool combustion temperatures. Reducing power will also help to lower EGT.
Cold Weather Precautions
Always visually check the crankcase breather line on a cold weather preflight. It is common for moisture-rich air that slips by the piston and enters into the crankcase to deposit ice on the inside of the crankcase breather line or pipe. If ice blocks flow out of the crankcase for excess pressure, oil will begin leaking from every seal on the engine and you will often blow out seals on the engine.
Detonation is different from pre-ignition. Detonation is the fuel/air mixture rapidly exploding inside the combustion chamber rather than a nice slow and even burn of the fuel. Detonation is generally caused by low octane fuel or very high engine temperatures. Roughness in the engine, high engine temperatures, and parts of the engine violently breaking or failing are all signs of detonation. If this occurs, lower the nose, cool the engine, reduce power, and enrich the mixture. (stop being cheap and running car gas in your airplane, use the appropriate avgas grade).
Preignition is the fuel/air charge igniting before it is supposed to in the combustion chamber (uncontrolled firing of the fuel/air in advance of the normal sparkplug spark to ignite it). It could be caused by a hot piece of carbon buildup in the engine, or something else igniting the fuel/air charge before it should. Symptoms are a rough running engine, loss of power, or high engine temperatures. The remedy is to enrich the mixture, lower the nose, reduce power, cool the engine. (starting to see a trend here huh?…..heat is bad for engines).