Overfilled Power Steering Fluid

Hydraulic power steering systems are designed to be completely sealed to transmit the motion of the steering wheel to the front wheels. Still, it’s a good idea to check the fluid level in the reservoir occasionally.

Let’s say you give it a quick look when you change your oil and notice it’s a little low, so quickly try to top it up before getting on with the rest of your day. Only you might have put in too much, which leaves you wondering what might happen if you overfill your power steering reservoir.

In the short term, you risk the excess fluid escaping the reservoir via the vent cap, which can make an awful mess in the engine bay. If it lands on something hot, like the exhaust manifold, there’s even a risk of it combusting or smoldering. It could also foul a lot of other engine components and the serpentine belt.  

To correct this problem and help you understand how to keep your car’s power steering system running smoothly, we will have to look at how the system works and the possible consequences of overfilling the power steering fluid reservoir.

How Does a Power Steering System Work

Car Tech 101: Power steering explained

Most of the power steering systems in modern cars are hydraulic and use pressurized hydraulic power steering fluid to translate the motion of the steering wheel with enough force to easily move the steering tires. Without this hydraulic pressure, you would only have the strength of your arms to move the front tires of your 2,000+ pound car!

The power steering fluid in the reservoir is drawn through the power steering pump, which is driven by a pulley connected to the serpentine belt. It has two sides: the non-pressure side, which is connected to the reservoir, and the pressure side, which is connected to the steering system rack or steering gearbox.

As the power steering fluid goes through the pressure sidelines, it is heated, which causes it to expand slightly in volume.

From the rack, there’s a return line that brings power steering fluid back to the reservoir, completing the cycle. If the reservoir is overfilled, the modest pressure and the heated, expanded fluid in the return line can cause power steering fluid to spray out of the reservoir.

It’s also worth noting that power steering fluid also helps lubricate the moving parts in the power steering system.

How Full Should the Power Steering Fluid Be?

How to Check & Add Power Steering Fluid with Scotty Kilmer

Most power steering fluid reservoirs are made from semi-translucent plastic with a MIN and MAX level stamped on it. So long as the fluid level is within those two lines, the system will have enough pressure and lubrication to let you steer the car effortlessly.

If your car has a dipstick attached to the cap, you can use it to get an accurate reading. Just be sure to wipe the dipstick with a clean paper towel and dip it again to get the most accurate reading.

Is It Bad to Overfill Power Steering Fluid?

Is It Bad to Overfill Power Steering Fluid

Overfilling your power steering fluid is more of a threat to other components in the engine bay than it is to your power steering system. When heated, expanded power steering fluid returns to the reservoir via the return line, which can cause the fluid to spray out of the relief valve on the cap. It then sprays all over the engine bay, which can wreak havoc in many different ways.

Power steering fluid is a lubricant, and there are several things in your engine bay, like the serpentine belt, that rely on a reasonable amount of friction or tension to run properly. If power steering fluid gets on them, it can affect the performance of all sorts of things.

While power steering fluid isn’t technically flammable, it is combustible. If it lands on something hot like the exhaust manifold, it starts a fire that can spread through the engine bay.  

What happens if I overfill the power steering fluid?

If you overfill your power steering reservoir beyond the MAX line, you’ll likely have an ugly mess on your hands. When the heated, expanded, low-pressure fluid returns to the reservoir, every milliliter beyond what the reservoir can hold will spill or spray out of the pressure relief valve on the cap. What this combustible lubricant fluid lands on will determine the next problem you have to deal with.

Here are some troubles that can be caused by power steering fluid overfilling:

1. A Slipping Serpentine Belt

A Slipping Serpentine Belt

The serpentine belt drives the power steering pump and is usually right next to the reservoir; when the power steering fluid lands on it, the lubricant can start to spread throughout the engine bay. Right off the bat, it’s going to cause the power steering pump to be underpowered, which you’ll notice as the steering feels stiffer than usual.

From there, the power steering fluid can cause the serpentine belt to slip on other pulleys, such as the alternator, air conditioning, and water pump pulleys. Any of which can affect the performance of the engine or the cooling system.

How to Fix

How to Replace a Serpentine Belt

If it’s only a small amount of power steering fluid, you might be able to pull the serpentine belt off. Then, soak it in a bucket of warm, soapy water while you meticulously wipe down all the pulleys with clean shop rags. After a good soak, you can wipe the belt dry, let it air dry, and try to reinstall it.

If the belt still slips or is completely soaked with power steering fluid, you might have to replace it with a new serpentine belt. This can run you from $25 to $75.

2. Foul the Alternator

Foul the Alternator

If the power steering fluid lands on the alternator, it can get into the brushes that it uses to produce electricity. This could be a double whammy from the lubricating effect of the power steering fluid, causing the pulley to slip on the serpentine belt while also preventing the brushes from working properly.

In such a case, you’ll usually get a battery warning light popping up on the dash. The ECU notices a steep decline in alternator performance and warns you about it before the battery goes completely flat. The worry here is that if it happens when you’re driving and you’re far from home or the closest repair shop, the fouled alternator will only get you so far before the remaining charge in the battery isn’t enough to supply the plugs with the spark they need to keep the engine running.

How to Fix

If you’re lucky and it’s just a few drops of power steering fluid, you might be able to remove the alternator and degrease it. Though if it’s a serious amount of power steering fluid, you might have to replace the alternator completely.

3. Smoking/Burning on the Exhaust Manifold

Smoke from around the exhaust manifold

Power steering fluid is combustible, which means it can light on fire if it lands on something very hot, like the exhaust manifold. Most of the time, you get a lot of smoldering and toxic, burning oil-like smoke. It can even come through the dash vents if they are set to fresh air rather than recirculate. The gummy oil also traps dust and dirt, making your engine bay look grimy.

How to Fix

Given enough time, the power steering fluid will burn off, which takes an annoying amount of time, and your engine and exhaust manifold will look hideously dirty. The easiest thing to do here is to blow an entire Saturday cleaning your engine.

Professional auto detailers can clean the engine and inspect common parts for signs of a problem for around $150 to $300.

How to Deal with Excess Power Steering Fluid?

The easiest way to remove excess power steering fluid from the reservoir is to draw it out with a simple turkey baster or a medicine syringe. Though there’s a risk here of drops escaping the tip or the outside of the syringe, and the serpentine belt is right there. So, if you’re going to go this route, make sure to lay down a few old towels first to catch any errant drips.

Professionals will use a suction extractor to draw out a specific fluid volume with far less risk of drips. You can replicate this with a simple siphon hose like you’d use to clean out your fish tank. However, putting down some old towels as dip insurance would still be best.

How to Properly Flush Your Power Steering Fluid for Optimal Performance

How to Flush Your Power Steering Fluid

Power steering fluid occasionally must be flushed and replaced, as it can slowly break down over time. If an O-ring or a seal has failed or some contaminant debris got into the reservoir, a proper power steering flush will help get it out while you make any other necessary repairs. You can flush and replace your power steering fluid using the following steps.

  • Step One: Jack up and block out the car.
  • Step Two: Find the low-pressure line in your power steering system. It runs from the steering rack or gear to the power steering fluid reservoir. 
  • Step Three: Disconnect the low-pressure line and carefully feed it to an oil drain pan. If it doesn’t reach on its own, you might need to add a length of rubber hose to keep it from making a mess. 
  • Step Four: Have a helper start the engine to allow the power steering pump to pull the old fluid out of the reservoir. As it gets lower, it starts adding more fluid to the reservoir.

It’s important to ensure the reservoir always has fluid to keep air from being drawn into the system.

  • Step Five: Continue to add new power steering fluid to the reservoir and watch the old, darker fluid come out of the low-pressure line. When new fluid starts coming out of the line, turn the car’s engine off.
  • Step Six: Reconnect the low-pressure line to the reservoir and burp the system to ensure any air has been pushed out.
  • Step Seven: Refill the reservoir with a new power steering fluid.

Can Overfilling Power Steering Fluid Start a Fire?

Overfilling Power Steering Fluid

Power steering fluid is combustible but not technically classified as flammable, which means it can burn but won’t readily light on fire. If you get enough of it on your exhaust manifold or something else that’s ripping hot in the engine bay, it might smolder to the point where it starts a fire.

Of course, the big worry here is that the flames are enough to burn rubber components or melt protective wire coatings. This is a whole other kettle of fish.

Frequently Asked Questions

Do You Need to Replace Your Power Steering Fluid?

On average, you’ll need to replace your power steering fluid every 40,000 to 80,000 miles, depending on the make and model of the vehicle. You can usually do this on your own in less than an hour. Just make sure to choose the right kind of fluid and put a few old towels around the reservoir hole to keep accidental drips from getting into the rest of the engine bay.

Do Electronic Power Steering Systems Use Fluid?

Some newer cars have electronic power steering systems that use electric motors to help turn the front steering tires. These systems don’t have any power steering fluid. However, some Electro-Hydraulic Steering systems on select models use an electric motor to power the pump rather than the serpentine belt. These systems do still use power steering fluid in the hydraulic components.

Excessive Fluid, Excessive Problems

Overfilling your power steering fluid reservoir is an easy mistake to make. If you put too much fluid in, and it warms up as it passes through the power steering system to the return hose, it can cause the power steering fluid to spray out through the release valve on the reservoir cap.

From there, it’s very easy for it to land on the nearby serpentine belt, which is right there, powering the power steering pump. This can foul the performance of all the other belt-driven components like the alternator, air conditioning compressor, and water pump. Power steering fluid that lands on the alternator can foul the brushes, making it difficult, if not impossible, for it to charge the battery.

Power steering fluid that spills out onto the exhaust manifold or other hot components in the engine bay can smolder with noxiously annoying smoke. Not to mention making a hideous mess by trapping dust and grime. There’s also a slight chance of it smoldering until it catches fire.

If you catch it immediately, you can easily remove the extra fluid from the overfilled power steering reservoir with a turkey baster or a medicine syringe. Just be sure to lay down some old towels first to catch the drips. Though the bigger concern in all of this is that the power steering system is supposed to be an enclosed hydraulic system. The reservoir shouldn’t have been low in the first place; if it was below the MIN line, you likely have a leak somewhere in the system!

Jason Farrell

Written By

Jason Farrell

Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.

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