Why your car won't start in the cold
A click, a slow crank, or nothing at all. What each one usually points to on a cold Ottawa morning, and what to check before you buy a battery.
Clicking, slow cranking and silence mean different things
Listen to what the car does when you turn the key or press the button. The sound narrows things down before anyone lifts the hood.
- Rapid clicking, like a fast ticking. The starter solenoid is trying to engage and dropping out because voltage collapses. Weak battery or a poor connection, most of the time.
- A single click, then nothing. The battery may be fine, and the starter motor or its solenoid is not turning over. Could also be a bad cable or ground.
- Slow, laboured cranking that may or may not catch. The battery is low or the engine is hard to turn, often both on a cold morning.
- Normal cranking, no start. The starting system is doing its job. The problem is fuel, spark or a sensor, and that is a different diagnosis.
- Nothing at all, no click, dash lights dim or dead. A flat battery, a corroded terminal, or a main fuse or cable problem.
Why cold mornings expose a weak battery
A battery is a chemical reaction, and cold slows that reaction down. At minus 25°C a battery has noticeably less to give than it did in September. At the same time, cold oil is thicker and the engine takes more effort to turn. The demand goes up exactly when the supply goes down.
That is why the first deep cold snap of the season is when tired batteries quit. The battery was probably getting weaker all summer, but warm weather hid it.
A battery’s cold weather strength is its CCA rating, cold cranking amps, measured at about minus 18°C. When you replace one, match or beat the rating your vehicle maker calls for. A cheaper battery with a lower CCA number may start the car fine in October and leave you stuck in January. If the battery is original and the car is five or more years old, test it before winter rather than after it strands you.
Won’t start but the battery is good
This is one of the most common things people say at the window, and usually it means the headlights came on. Headlights draw a few amps. A starter can draw well over a hundred. A battery can light the dash and still collapse the moment the starter asks for current.
So the first step is a proper load test, not a voltmeter reading at rest. If the battery really does pass, the next places to look are:
- Battery terminals and cable ends, including corrosion hidden under the clamp.
- The ground strap between the engine and the body, which corrodes in salt season.
- The starter motor and solenoid, tested with a voltage reading at the starter while someone cranks.
- The ignition switch, the clutch or neutral safety switch, or a key the anti theft system no longer recognises.
When the alternator is the real problem
If you boost the car, it starts, and then it is dead again a day or two later, the battery may not be the cause. The alternator charges the battery while the engine runs. If it is weak, every drive takes a little more out than it puts back.
Short winter trips make this worse even with a healthy alternator. Heated seats, the rear defrost, the blower on high and the headlights all draw power, and a ten minute drive to the grocery store may not replace what the cold start used. A slow drain from a module that does not go to sleep, or an aftermarket accessory, can also flatten a battery overnight.
That is why we test the battery, the starter and the alternator together. One failing often takes another with it, and a new battery on a car with a bad alternator is a new dead battery in a week. The battery, starter and alternator page covers what the testing involves, and drains that are harder to trace are an electrical diagnosis.
Block heaters
A block heater warms the engine coolant, and with it the block and the oil, before you start. The engine turns over more easily, oil reaches the bearings faster, and you get heat in the cabin sooner. In Ottawa it earns its keep on the minus 20°C mornings.
You do not need it plugged in all night. A timer that switches it on a few hours before you leave does the job and saves power. Check the cord each fall for cracks and chewed insulation, since it hangs at the front of the car in the slush all winter.
Oil thickness matters in January
The first number on a bottle of oil, the one with the W, describes how it flows cold. A 0W oil flows more easily at start up than a 5W oil, which flows better than a 10W. Thinner cold oil means less drag on the starter and faster lubrication in the first seconds after a cold start.
Use the grade your owner’s manual specifies. Many newer engines are built for 0W20 or thinner, and putting something heavier in to be safe makes cold starts harder, not easier. If your car is due for service before winter, the oil change and maintenance visit is a good time to have the battery tested as well.
If it will not start at all, you can still book online and describe what it does when you turn the key. A short video of the sound helps.
Questions people ask
Why does my car just click when I try to start it in the cold?
Rapid clicking usually means the battery cannot supply enough current to turn the starter, either because it is weak or because a terminal or cable connection is poor. A single loud click with no cranking points more toward the starter or its wiring. A load test of the battery and a voltage check at the starter tell them apart.
My car won't start but the battery is good. What else could it be?
Headlights and the radio draw very little current, so a battery can power them and still fail to crank the engine. If the battery really does pass a load test, the next suspects are corroded or loose cables, a bad ground, the starter, the ignition switch or the anti theft system. If it cranks normally but will not fire, the problem is fuel, spark or a sensor.
What does CCA mean on a car battery?
Cold cranking amps, the current a battery can deliver at about minus 18°C for 30 seconds while holding a usable voltage. A replacement battery should meet or beat the CCA rating your vehicle maker specifies. In an Ottawa winter that number matters more than the brand.
Related work
Book it tonight
Pick a time on the booking page whenever it suits you, describe what the car is doing and add a few photos. Drop it off on the day you picked, before 4pm.
