Ultimately an electric block heater derives the power it uses for heating from mechanical energy transmitted via the belt to the alternator. If one wants a block heater just for reducing time until cabin heat works, rather than for starting the engine, it seems like rather than putting wear on the alternator and battery dumping through a big resistor, it would make sense just to add mechanical resistance on the belt, forcing the engine to work harder, until it heats up.

Has this been done? Is there a reason it wouldn't work well? Are there any kits to do it?

  • Well, you could just drive it - that puts a load on the engine....
    – Solar Mike
    Oct 11, 2018 at 19:22
  • @SolarMike: Yes, that kinda works if you drive it in first gear or just rev the engine way up in neutral, but... Oct 11, 2018 at 23:40
  • After 40mph approx, the load caused by air resistance is greater and inreases proportionalky with speed - which is why small or low engine power cars run out at 120 or so mph and more powerful cars have higher top speeds, but once the engine power is equal to the opposing load then no more increase in speed...
    – Solar Mike
    Oct 12, 2018 at 4:01

2 Answers 2


They use a resistor because it is the cheapest and most reliable (reliable as long term maintenance-free) method to produce "startup" heat. Granted, there is some strain onto the alternator and battery, but both are usually upgraded when equipped with an additional heater.

The mechanical resistance method would need some kind of friction coupling, subject to wear, tear and cost: Mechanical clutches/brakes do experience wear. Fluid resistance systems (similar as a calorimeter) need to have the fluid checked and are subject to seal ring wear. In all systems are some kind of clutch involved as you want to release the additional load when the engine is warmed up.

So in sum: It increases weight, risks, maintenance, complexity and costs.

The detriments are quite severe, especially since the following alternatives are already established:

  • Some electrical heater, either powered by the battery or mains.
  • A fuel powered, auxiliary heater. Available as air-heater or coolant-heater.

The mentioned auxiliary heater is also available as a pre-heater: This is the best (and most expensive) of them as the vehicle is already warm, the engine (in case of a coolant-heater) is also warm and the windows are defrosted when you enter the vehicle.


I know of a company who had a patent on a clutch/ belt driven auxiliary coolant heater. Remember as engines become more fuel efficient the give off less heat. And diesel engines generally give off little heat. This aux heater used spinning disks to create fluid sheer directly to the engine coolant. Don’t know if they ever went to production. I always thought those guys were just too greedy in their pricing.

But customer warm up is a significant issue when it gets cold outside. How long does it take to defrost an iced windshield? How long to get comfortable inside the car when its 0 degrees F outside? Some engines are so efficient they will never get warm at engine idle, no matter how long they run.

Its a tough problem. Good fuel efficiency is generally good for saving money. Its just bad for generating heat.

So yeah others are looking at the issue.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .