Rick's Free Auto Repair Advice

Car won’t start in cold weather

What to do when your car won’t start in cold weather

Diagnose car won’t start in cold weather

Diagnosing a car won’t start in cold weather condition is similar to diagnosing any other type of car won’t start condition. In other words, start with the basics: fuel and fire.

How to test for spark

If your engine uses spark plug wires, check for spark by removing one of the spark plug wires from a plug and hold it about a half-inch away from the top of the plug while someone cranks the engine. You should hear a sharp cracking noise as the spark jumps the gap to the spark plug.

If you can’t get the spark to jump the gap, you may need a tester. Here are three types:

Lisle 20610 inline spark plug tester

Install the Lisle 20610 inline spark tester between the spark

test for spark

Inline spark plug tester

plug wire and the spark plug. Then crank the engine and watch the spark jump across the gap in the window area

Lisle 19380 Spark Tester

Slide the grooved portion of the tester over a spark plug wire

test for spark

Spark tester for spark plug wires

and crank the engine. The Lisle 19380 Spark Tester includes an inductive pickup that lights a neon tube inside the tester every time it detects high voltage discharge.

Test coil-on-plug ignition system

If your car has a coil on plug ignition, you’ll need a special tester to see if the coil is firing. Waekon-76562 Quick Variable Sensitivity ignition coil tester is designed to give a visual indication every time a coil on plug coil fires. Just hold the sensor end on the coil and watch for the visual indication.

test ignition coil

Waekon 76562 coil on plug tester

test coil

Waekon coil on plug tester in use on engine’s fuel injectors

You’ll also need a special tool to check for fuel injector firing. The Waekon 76462 Universal Electronic fuel injector tester works just like a coil tester. Simply place the probe on the injector and it lights up when the injector fires.

test fuel injector

Fuel injector tester

If the coil and fuel injectors fire

If the ignition coil and fuel injector fire, you should get combustion and engine fire up.

But there are other issues that can cause a car won’t start in cold weather. Let’s talk about those.

Is the engine cranking at the right speed?

Motor oil thickens when cold, causing more friction and reducing engine cranking speed. But cold weather also reduces the chemical reaction inside the battery, lowering its voltage and amperage output. In addition, corrosion on the battery posts and terminals can dramatically lower the power available to the starter.

If your engine isn’t cranking at the proper speed, it won’t start even if it has spark and fuel. An internal combustion engine requires at least 100 RPM to start. If your engine is cranking slowly, check the battery charge level using a digital multimeter.

Check battery voltage

These are the voltage reading for a maintenance-free battery at various charge levels and temperatures.

Battery voltage at 50°F

Fully charged 12.77 volts, 50% charged 12.37 volts, 25% charged 11.97 volts, 0% charged 11.77 volts

Battery voltage at 20°F

Fully charged 12.56 volts, 50% charged 12.15 volts, 25% charged 12.032 volts, 0% charged 11.80 volts

Battery voltage at 0°F

Fully charged 12.66 volts, 50% charged 12.26 volts, 25% charged 11.86 volts, 0% charged 11.66 volts

If your battery voltage is at 25% charge or lower, it’s probably not providing enough power to crank the engine at a fast enough speed to start. Charge the battery or buy a new one.

©, 2018 Rick Muscoplat




Posted on by Rick Muscoplat

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