Reader Question: Block Heaters?

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Here’s the latest reader question, along with my reply! 

Troy asks: When I was a kid, I remember seeing people regularly using block heaters to help warm up their cars in winter. I don’t see them as much anymore. Any reason for that?

My reply: It depends on where you happen to be. If you live in an area where the winters are hard and long, you’ll still see extension cords running from inside the house to the car outside.

And under the hood.

The idea is to reduce cold-start wear and to increase the life of the battery, which works extra-hard t start a car when it’s significantly colder than freezing outside. The heater is usually a magnetic pad you slap onto the bottom of the oil pan or something that slips into the oil dipstick or radiator, depending on the type. These don’t really keep the engine warm – they just keep it from achieving “thermal equilibrium” with the outside air temp!

But you may not see them as much – chiefly because modern fuel-injected cars start easier than the carbureted cars of the now-distant past (cars have been fuel-injected since the late 1980s) and “warm up” much faster.

In the old (carbureted) days, it could take several minutes in very cold weather for the idle to stabilize, the choke to release and the car warmed-up enough to drive easily. Today, it’s sound policy to begin driving almost immediately after the engine is started.

But it’s still good policy to drive the car gently for the first several minutes, in order to give the rest of the drivetrain (and lubricated parts) time to get lubed-up and warmed up.

A tip: If the vehicle has a manual transmission, gently ease out the clutch (with the shifter in neutral) and let the engine idle a moment or so before driving off. This will circulate lube inside the transmission, which should result in noticeably smoother shifting on very cold days and probably help reduce wear and tear on the transmission, too.

. . .

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  1. My first car was a Chevette with a manual transmission (manual everything, pretty much…only thing I recall that was automatic was the choke). My first year of college, I drove off to Illinois. Things got interesting in the winter months, once things got cold enough that the snow would stick around. For the first couple or three minutes, changing gears felt like the other end of the stick was moving through molasses. As it warmed up, it loosened up until it behaved normally.

    I’d try that idling-in-neutral trick, but (1) I no longer have a car with a manual transmission (at the last opportunity I had to buy one, I let the salesman talk me out of it) and (2) we don’t get much truly cold weather here in Las Vegas. 🙂

  2. Most block heaters of the factory style are installed in a freeze plug port. The wife’s car, being that strange V-6 turned the wrong direction was the first vehicle I’d had in a while that didn’t have one.

    I didn’t put one on the Z71 cause I didn’t ever think about it and didn’t value it very much(a bad reason to not give the engine a break).

    It’s nice to get into a vehicle, fire it up and it’s already close to 100 degrees and is in just a couple minutes so you can melt the ice on the windshield without the trauma of scraping or alcohol or such. I like that the oil pressure doesn’t go way up and the transmission benefits since it’s bolted to the heated block. It’s especially nice when one is in the barn and is warm with no ice on it. I guess that block heater works well on manual transmissions too since I never had one that was hard to shift with an engine block heater on the vehicle.

  3. Most real block heaters are installed in a coolant hose and the warmed fluid circulates through the engine by convection. Makes the engine start like a summer morning and takes a lot of wear and tear off of everything. I plug in either the night before or when I first get up (or not at all) depending on the forecast low.

    My experience is that a carb and manual or properly working automatic choke will start faster and more reliably in sub-zero weather, but that FI if it starts will let you drive right off instead of waiting to warm up the manifold and carb.

    It’s always fun in really cold weather when you don’t have to use the brakes at all until all the gear oil warms up.

  4. I remember attempting to drive the Subaru XT on a sub zero morning. Started just fine but the gear shift wouldn’t move. Forced it into neutral and let it sit for a few minutes to get the oil moving.


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