Cold Weather Starts

Operating small general aviation (GA) piston engines in coldweather presents unique challenges and risks that require us to adjust procedures to ensure safe, reliable starts and avoid damaging the engine. Cold temperatures affect fuel vaporization, battery performance, oil viscosity, and starter motor longevity, making a standard warm weather start procedure ineffective or possibly even harmful.

Cold weather affects several aspects of engine starting andoperation. The higher density of cold air means a richer fuel mixture is necessary for ignition, as fuel does not vaporize as readily in freezing conditions. Batteries also lose effective cranking power, reducing the energy available to start the engine. Oil thickens in low temperatures, increasing resistance and wear during engine rotation. Additionally, starter motors risk
overheating with prolonged use.

Appropriate adjustments to our procedures must be made. Wemust understand that cold weather demands a refined approach to priming, throttle use, starter operation, and engine warm-up to ensure smooth, damage-free starts.

One of the most effective ways to protect the engine in coldweather is preheating before start. Preheating raises cylinder and oil temperatures, reducing oil viscosity and improving fuel vaporization. It decreases wear on the engine’s internal components caused by cold starts—the most damaging wear often occurring in the first minute of operation when lubrication is minimal. Safe and effective preheating is its own subject. Just research and follow proper procedures and never leave the airplane unattended during preheat operations.

Proper priming is crucial to compensating for the dense coldair and ensuring an adequate fuel/air mixture for combustion. Unlike warm starts where minimal primer strokes suffice, cold weather demands more priming
strokes to deliver sufficient fuel to the cylinders. However, this must be balanced carefully to avoid flooding the engine. Over priming is a common cause of engine compartment fires. Follow the engine manufacturer’s procedures for priming. We also realize that each airplane is different, so seek the advice of pilots who may be familiar with the specific airplane.

Throttle and mixture settings usually do not vary much fromnormal, warm weather starts but check and follow what the manufacturer recommends. Some, but not all, small GA airplanes have a small pump, sometimes
called an accelerator pump, as part of the throttle assembly. If the airplane has an accelerator pump, Pumping the throttle may help with cold starts, but can also flood the engine possibly inviting a fire. Again, follow the
manufacturer’s recommendations.