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As I currently reside in an area which experiences cold* winters, and do not have access to a garage, I started considering getting an electric block heater. The design I have in mind is installed in the coolant circuit. It consists of a heating element, a coolant pump and a mains power supply. The car is plugged in up to 4 hours prior to being used, and the device will heat the engine coolant to operating temperature.

The car is a 2005 Audi A4 2.0 TFSI.

Benefits I expect is that the heating will provide warm air right from the start, helping me defrost the windows and prevent ice from forming on the inside as I get into the car; also that the starter has less work to do as the oil is less viscuous, which reduces the strain on the battery.

Will the block heater provide a real benefit here (and possibly in other areas) on this kind of vehicle?

*cold = currently -15°C during the day, temperatures close to -30°C during the day not being unheard of

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  • How cold is "cold"? If the temps are regularly below 0 F, then I'd say sure that sounds like a good idea for the reasons you listed. If the temps are more like 25 F, I'd say it's not worth it. Your engine is small and will warm up quickly by idling for a couple minutes. Also note that a coolant heater will warm the oil a bit, but if you really want to warm the oil then you should get an oil heater.
    – the_storyteller
    Commented Jan 19, 2021 at 20:41
  • @the_storyteller I added the temperature range the car needs to deal with. Heating the oil is one thing, getting warm air from the vents right from the start is another thing I am interested in.
    – user149408
    Commented Jan 19, 2021 at 20:49
  • A block heater might warm your engine 30 to 40 degrees above ambient temperature, but not enough to make "warm air from the vents right from the start".
    – Arthur Kalliokoski
    Commented Jan 20, 2021 at 6:11

2 Answers 2

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As I currently reside in an area which experiences cold* winters, and do not have access to a garage, I started considering getting an electric block heater. The design I have in mind is installed in the coolant circuit. It consists of a heating element, a coolant pump and a mains power supply. The car is plugged in up to 4 hours prior to being used, and the device will heat the engine coolant to operating temperature.

Will the block heater provide a real benefit here (and possibly in other areas) on this kind of vehicle?

Absolutely, especially for a heater in the coolant circuit!

There are several types of block heaters:

  • A true old-fashioned block heater installed in a freeze plug. They are typically reasonably good.
  • An "oil heater" attached to the side of an engine block. These typically have rather low power (example: 300 watts) and the main benefit is that the oil viscosity isn't as big issue when starting the engine since they heat the oil. You'll have to wait for a long time to get heat from the engine, though. I used to have one in my previous car (2011 Toyota Yaris), and it does indeed make it a bit easier to start.
  • A heater installed to the coolant circuit. Especially the ones that have not only a heater but a circulating pump, the power can be quite high (example: 700 watts). I have a 700 watt unit in my current 2016 Toyota RAV4 hybrid and it's very useful.

When installing a block heater:

  • Install electrical wiring to the footwell of the passenger so that you can later install a cabin heater. This cabin heater will mean the windows won't have any frost when starting the car, and the inside of the car will be warm. These typically draw quite a lot of power though (example: my current cabin heater is 0W/1100W/1900W selected by a switch and I use it at 1900W).
  • Consider whether you want to permanently install a lead-acid battery charger so that the lead-acid battery won't drain if you drive short trips. I have a 12 volt 4 ampere lead-acid battery charger in the same wire as my block heater in my 2016 Toyota RAV4 hybrid, so my lead-acid battery will never get drained. As this car is a hybrid, the load on the lead-acid battery is not that big, but it's useful nevertheless if using the heated windshield often as it's powered by the 12-volt circuit and not by the high voltage hybrid circuit.

I use the heater with a 2-hour timer. The 700 watts will heat the engine well enough in 2 hours, and the 1900 watts will heat the inside of the car well enough too in 2 hours.

4 hours is excessive in my opinion unless the heater is underpowered ...in which case it won't be of much use in the coldest days.

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  • Thanks! The block heater type I have in mind is of the kind that splices into the coolant circuit, with its own pump. A battery charger/tender is another thing I am considering, but responses suggest it would be best to install that in the passenger compartment (possibly near the relays in the driver footwell) as these devices might not cope well with moisture. That means I’d have 220V wiring in the cabin already.
    – user149408
    Commented Jan 21, 2021 at 19:07
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I have a small fan heater (500W) that I put under the bonnet of my car and run it for a couple of hours early morning.

The car starts first time no hassle, but if I leave it to get cold and then try to start it, it takes 4 or 5 attempts and hammers the battery and starter. It is a 2.2 diesel...

So, I went the cheap route and it makes such a difference, try it and see.

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