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I don't know if I should get electric or hydraulic (where you put the fluid in) power steering...

What's the difference between the two in terms of how they work?

Is one more efficient at steering than the other?

Which one is more reliable (in terms of repairs)? Stats would be nice ;)

What are the disadvantages and advantages of each one?

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What's the difference between the two in terms of how they work?

In both cases, the power steering simply adds some force to the steering when it detects the driver is trying to turn the wheels. Simply, in one case there is an electric motor to add this force, while in the other hydraulic liquid is used.

Is one more efficient at steering than the other?

A hydraulic pump is always in motion while the engine is on. Since any hydraulic system has some internal friction, this means the engine has to consume some power to turn it. The steering pump is permanently connected to the engine crankshaft through a belt and pulley, which also takes some power to keep turning.

On the other hand, an electrical power assist will only draw power when it is actually being used (i.e. the driver is turning the steering). The electrical system also uses an existing source of power, the car alternator - that is already a required piece of equipment for the other needs of the vehicle. But, lacking the extra pulley and pump needed by a hydraulic steering system (and perhaps also an extra belt, depending on engine design), some energy savings are to be expected.

Which one is more reliable (in terms of repairs)? Stats would be nice ;)

No stats ... perhaps because electrical power assist is still a relatively recent technology. Even so, since electric systems have less components and no hydraulic valves and gaskets (so no leaks!), in theory they should be more reliable than hydraulic. In practice, hydraulic power assist has been around for very many years, so it has the advantage of being a well-known, mature technology.

What are the disadvantages and advantages of each one?

The feeling of each system is slightly different from the driver's point of view. From an objective standpoint, perhaps the only statement that can be made is that hydraulic assistance dies instantly when the engine is turned off. Some electrical systems can be programmed to continue running from the battery, though this should be avoided for extended periods of time since the battery will drain. Electric systems can also be perceived to be slightly more reactive to driver input.

From a subjective standpoint, each driver could test different cars with each of these systems to find out which suits best his/her purposes and driving style.

  • One concern which has always nagged me relates to whether one could steer an electrical power-steered vehicle if the battery is flat. Could you elaborate on this in your answer? – Zaid Jul 26 '15 at 9:08
  • In addition to what you said about efficiency, you also need to think about the pulley which drives it. I was told a long time ago that every pulley on the car pulls 5hp. This was really important when there was multiple v-belts running all of the different accessories. Then along came the serpentine belt which cut down on the number of pulleys. Whether or not it actually soaked up that much power, it does take power to run them. Consolidating the power steering pump over to the alternator is going to free up power and be more efficient in the long run. – Pᴀᴜʟsᴛᴇʀ2 Jul 26 '15 at 10:31
  • @Zaid I have done so, and it works as long as the engine is on. Starting a small city car with a flat battery (Fiat Panda Diesel) by throwing it downhill was not a pleasant experience: very hard steering until the engine kicked in, then a rather brutal transition to the usual very soft steering. – ALAN WARD Jul 26 '15 at 14:24
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    @Paulster2 Good one, I am making an edit to the answer along these lines. This is perhaps one of the reasons European cars lacked A/C until average engine displacement went up a bit - as you say, the pulley is always "on" even if the compressor itself is not engaged. – ALAN WARD Jul 26 '15 at 14:27
  • Every pulley pulls 5hp? That sounds awfully high. I can believe that for the AC compressor, but e.g. an alternator that requires 5 hp would put out 3.5 kW or 290 A (minus a bit of friction and conversion loss). Not many alternators are that powerful. – Hobbes Feb 4 '17 at 21:17
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I will provide my opinion which is slightly different from the accepted answer.

If at all possible, choose a car with electric power steering! Rubber parts in old cars can will fail. A hydraulic power steering rack needs to have oil seals made from rubber.

Nobody is willing to repair a power steering rack due to the fact that the steering is perhaps the most safety-critical system in the car. If the car suddenly turns to the direction of the opposite traffic due to an improper repair, people will get killed.

I used to have a 1989 Opel Vectra. When in 2010 the power steering rack failed (started to leak oil), the only option was to get a junkyard part, because no new parts were being made. The price of the junkyard part alone was absurdly high: several hundred dollars -- apparently, these parts are in high demand. Guess what happened to the junkyard part? Yep, it failed in 2011, because the junkyard part had obviously old rubber parts too. The car had no exploding steering wheel (a.k.a. airbag), so labor charges were probably lower than in modern cars.

On an engine, it is not a problem if rubber seals fail. You don't need a new engine. Just new seals will be fine. Similarly for practically any component on a car. Steering is the exception: nobody is willing to repair a steering rack.

Although electric power steering is a relatively new technology, the fact that it needs no rubber seals is enough to guarantee that it will be less of a maintenance burden than hydraulic power steering. When choosing a car, please keep in mind that there are hybrid electric-hydraulic systems that have a hydraulic power steering rack but the pump is electric. The worst from both worlds: part of the technology is very new, and part of the technology is such that it eventually will fail.

And, considering the success of Toyota hybrid cars which are probably more reliable than conventional gasoline cars, you shouldn't be afraid of new technology.

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According to car magazine tests I've read, electric power steering (especially on early cars with EPS) often lacks feedback: the forces acting on the wheels can't be felt in the steering. I had one of those early ones (2008 Audi A3), and the steering is pretty much dead. Some recent cars with EPS have better feedback.

Hydraulic power steering can be tuned to give decent feedback, although there have been plenty of cars with HPS and no feedback at all (e.g. American cars, Citroëns).

One big difference in functionality is that EPS makes it easy for the car to control the steering autonomously, and to give feedback (e.g. lane departure warning by making it more difficult to steer out of the lane, or by vibrating the wheel).

  • You are correct: I have driven both hydraulic and electric power steering cars, and the hydraulic (and thus also hybrid electric-hydraulic that has hydraulic rack but electric pump) definitely has a better steering feel. But I would never buy a technology that is pretty much designed to fail in 20 years, no matter how good it feels to drive. Once you get through the initial shock of driving EPS cars, you get used to the different steering feel. – juhist Feb 4 '17 at 21:48

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