Block Heater vs Battery Warmer: Which Helps a Cold Start More?
4 lessons in this series, 13 min in total
- Do Car Battery Blankets Work? 4 min read
- Battery Blanket vs Battery Maintainer: Which Do You Need? 3 min read
- Block Heater vs Battery Warmer: Which Helps a Cold Start More? 3 min read
- At What Temperature Should You Plug In a Block Heater? 3 min read
This lesson draws on Natural Resources Canada, Ford owner’s manuals, Rick’s Free Auto Repair Advice, Zerostart’s Heat Magnet data sheet and the retailer etrailer’s Kat’s product page and expert answers. How we research explains the method.
What each one heats
A block heater is an electric element in the engine’s cooling system. Ford’s manuals describe a heater element installed in the engine block that warms the coolant. Natural Resources Canada (NRCan) explains the chain: the warm coolant warms the engine block and its lubricants, so the engine starts more easily and reaches its operating temperature sooner.
A battery warmer is a heated wrap around the battery, usually 60-80 W. It keeps the battery warm so it can deliver more of its power, but the engine and its oil stay as cold as the night.
So the two attack different halves of a cold start. A block heater makes the engine easier to turn; a battery warmer makes the battery better at turning it. When thick, cold oil is the main drag, warming the engine does more.
Does your car already have one?
Some vehicles come with a factory block heater; Ford’s 2020 Explorer manual lists it as “if equipped.” Look for a short cord ending in a plug with a protective cover. Ford’s 2018 Super Duty manual puts the cord in the front tow hook pocket, while the Explorer manual mentions a cord under the hood.
Check your owner’s manual for a section like “Engine block heater (if equipped).” If you find one, you only need a grounded outdoor extension cord and, ideally, a timer. When to plug in a block heater covers temperatures and run times.
The three aftermarket options
| Heater | What it warms | Fitting | Notes |
|---|---|---|---|
| Frost-plug (core plug) heater | Coolant inside the block | Mechanic job: coolant drained, a core plug removed | Most effective, per Rick’s; sized to the engine |
| Magnetic heater | Oil pan from outside | Sticks on, comes off | Needs a steel surface; not aluminum pans |
| Battery warmer | Battery only | Wraps on | No thermostat; for below 32°F (0°C) |
Frost-plug heaters replace one of the engine’s core plugs, so each one fits specific engines. Rick’s Free Auto Repair Advice calls the freeze plug heater the most effective type, and on some engines the hardest to install, since it means draining the engine and removing a core plug. Have a mechanic choose and fit one for your engine.
Magnetic heaters stick to the oil pan. Rick’s is skeptical: it says they warm oil sitting in the pan rather than in the engine, so they do little for cranking, and many lack the wattage for extreme cold. If you still want one, Zerostart’s data sheet for its 300 W, 120 V Heat Magnet (part 3400021) lists oil pans among its uses and says it suits non-aluminum engine blocks. A magnet won’t hold on an aluminum pan, so check yours first. A built-in thermostat keeps it under 266°F (130°C), and it has a 6 ft (1.8 m) cord.
Zerostart 3400021 Heat Magnet
A 300-watt, 120 V magnetic heater for steel oil pans and non-aluminum engine blocks. Zerostart says a built-in thermostat keeps it under 266°F (130°C). A magnet won't hold on an aluminum pan.
Key specs
- 300 watts, 120 V
- Thermostat keeps it under 266°F (130°C)
- 6 ft (1.8 m) cord
- Not for aluminum oil pans
Paid link
View on Amazon (opens in a new tab)When a battery warmer is the better buy
A battery warmer makes sense when the engine has no block heater and you’d rather not have one fitted, or when the battery, not the engine, is the weak link. It is also the easiest of the three to fit, and it can move to your next car if the battery is a similar size.
Etrailer’s experts say the Kat’s 80 W wrap has no thermostat and should run only below 32°F (0°C), on a timer or overnight. Measure your battery first; do battery blankets work has the sizes.
Kat's 22200X Thermal Battery Wrap
An 80-watt heated vinyl wrap for common car and truck batteries that plugs into a household outlet. Etrailer's experts say it has no thermostat and should run only below freezing. Measure your battery first.
Key specs
- 80 watts, 36 in (91 cm) long
- Etrailer lists groups 24, 24F, 27, 27F and 74
- No thermostat: use below 32°F (0°C)
Paid link
View on Amazon (opens in a new tab)Where it gets very cold, you may want both. NRCan’s case for the block heater is fuel as well as starting: it says block heaters can improve overall fuel economy by as much as 10 percent at -4°F (-20°C).
Sources
Show all 6 sources Hide sources
- Natural Resources Canada: Idling ready-to-use facts (block heaters)
- Ford 2020 Explorer owner’s manual: Engine block heater
- Ford 2018 Super Duty owner’s manual: Engine block heater
- Rick’s Free Auto Repair Advice: Choosing the right engine block heater
- Phillips & Temro: Zerostart Heat Magnet data sheet, 3400021 (PDF)
- etrailer: Kat’s Heaters thermal battery wrap KH22200, 80 W
