Plug In Your Block Heater 2 to 4 Hours, Not All Night

What is the purpose of an engine block heater?

It warms the engine before you start it. Most models heat the coolant, and the warm coolant warms the block and the oil. The engine cranks easier, warms up sooner, and you get cabin heat faster on a below zero morning.

Most heaters you'll see on a car fall into a few types. The Block heater page on Wikipedia lists the main ones.

Freeze plug types tend to be the cheapest part and the hardest job, per Capital One's car guide (February 7, 2024). Many trucks and some cars come with one from the factory. Check before you buy.

At what temperature do you need an engine block heater?

Around zero and colder. Ram recommends its heater below 0 degrees and requires it below 20 below. Capital One's car guide puts the line for modern cars at 5 degrees or lower. Above that, a healthy gas car with the right oil starts fine without one.

Ram's 2022 Heavy Duty owner's manual gives the clearest numbers in print. Recommended below 0 F. Required below minus 20 F. Plug in for at least one hour.

So how often does Milwaukee get there? The count below comes from daily lows at Milwaukee Mitchell airport in NOAA's Applied Climate Information System, 31 winters from 1995 to 2026.

Over all 31 winters, the average is 12.9 mornings at 5 F or colder and 6.3 at zero or colder. The worst was 2013 to 2014, with 28 mornings at zero or below. The 20 below line that makes Ram's heater a must came in only two winters, 1995 to 1996 and 2018 to 2019.

That's the Milwaukee answer. A block heater earns its keep on a handful of mornings each year. On those mornings it matters a lot.

Can I leave my engine block heater plugged in all night?

You can, but it wastes power. Natural Resources Canada says two hours is more than enough. Tests from the 1970s found little gain past four hours. Put a timer on it and set it for two to four hours before you leave.

The two hour advice comes from Natural Resources Canada's idling facts. The same page says a block heater can improve fuel economy by as much as 10 percent at minus 20 C, which is minus 4 F. On a single short trip at minus 25 C, about minus 13 F, the savings can reach 25 percent.

The four hour limit comes from older lab work. Per the Wikipedia summary of 1970s tests run from 20 below to 12 above, coolant rose almost 36 F in the first four hours. Two more hours added only about 5 F. Oil warmed far less, about 9 F over the same time.

• Get a timer. An outdoor plug in timer set two to four hours before you leave does the job.
• Use the right cord. Ram calls for a grounded, three wire extension cord on a 110 to 115 volt outlet.
• Never use a two prong adapter. Skip the ground and you lose the safety it gives you.
• Unplug before you drive. Pulling away with the cord attached tears the plug off the car.

How much does a block heater cost to run?

About 14 cents an hour on a typical 715 watt heater at We Energies' 2026 home rate. Two hours on a timer costs about 28 cents. A full night of 10 hours costs about $1.40.

The math is simple. Ram rates its heater at 110 volts and 6.5 amps, which works out to about 715 watts. We Energies' residential Rg 1 energy charge is $0.19342 per kWh, plus small fuel and environmental charges, for about 19.6 cents per kWh, effective January 1, 2026, per its 2026 electric rates sheet.

Now scale it to a winter. Say you plug in on 30 cold mornings for two hours. That's about $8.40 for the season. Leave it on all night those same 30 nights and it's about $42. The timer pays for itself fast.

Installing One, and What It Costs

Install cost is the part plus the labor. Capital One's guide says most heaters cost under $100 before labor. Labor depends on the type and on your engine. A pad or dipstick heater is a short job. A freeze plug heater on many engines means draining the coolant, reaching a plug low on the block, then refilling and bleeding the system.

The table below uses this site's posted rates. A $150 call out covers the trip, a scan and the first 30 minutes. After that, labor is $150 an hour in half hour steps.

These are worked examples from the posted rates, not fixed prices. Engines vary too much for that. Give your year, make and model on the phone and you get a real number first.

One more thing before you spend money. A block heater does not fix a weak battery. If the car is already slow to crank in October, get the battery tested first. The cold start guide covers why cars won't start in the Milwaukee cold.

Asked and Answered

Are engine block heaters necessary?

Not for most gas cars in Milwaukee. Mitchell airport hits zero or colder on about 6 mornings a winter, by our count of NOAA records. Diesels, older engines and cars parked outside gain the most. Below 20 below, some truck makers require one.

That count comes from the NOAA ACIS daily lows in the table above. A diesel truck is the exception. Diesel engines are harder to start cold, and the Ram manual's 20 below rule is written for one.

How do you know if your car has a block heater?

Look for a short power cord with a three prong plug and a rubber cap. It's usually tucked behind the grille or the front bumper. Some sit in a hole in the lower air dam. Your owner's manual will list it as an engine block heater or engine coolant heater.

On the Ram Heavy Duty trucks, the manual says the cord sits behind the front bumper and comes out through the right hole of the air dam.

How do you tell if a block heater is working?

Plug it in for an hour on a cold day, then feel the engine near the heater or the upper radiator hose. It should be warm, not ice cold. If it's cold, check the outlet, the extension cord and the heater cord before you blame the heater.

A cord that got pinched in the hood or run over in the driveway is a common fault. So is an outdoor outlet with a tripped GFCI. The element itself can also burn out, and that part is a repair.

Is it better to use a block heater or idle the car to warm it up?

Use the block heater. Idling warms the engine slowly and burns gas at zero miles per gallon. FuelEconomy.gov says most makers recommend driving off gently after about 30 seconds. The heater gets the engine partway there before you turn the key.

Per FuelEconomy.gov, a gas car can lose 15 to 33 percent of its mileage on short trips in the cold. Natural Resources Canada says two to three minutes of idling is usually enough even on a cold day. Scrape the glass, start it, and drive gently for the first few miles.

Cold Start Help Where You Park

We come to the car, at home, at work or on the street. The $150 call out includes a real battery and charging test, and a look at the coolant if a block heater is on the list. If your car needs a heater fitted or a dead one replaced, you get the price before we start. See cooling and heating, batteries and starting, or the full price list. Call (414) 877-8092.

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