Low Brake Fluid: Effects, Symptoms, Causes & More
What is Brake Fluid?
Brake fluid is the high boiling point hydraulic fluid that is used in braking systems. It provides hydraulic pressure to activate the brakes when the brake pedal is pressed.
Brake fluid serves a few critical purposes:
- It transfers force into pressure to activate the brakes
- It lubricates and protects the components in the brake system
- It must maintain a high boiling point to operate properly under high temperatures
There are different types of brake fluid for different vehicle applications:
- DOT 3 brake fluid has a minimum dry boiling point of 401°F. It is suitable for disc and drum brakes.
- DOT 4 brake fluid has a minimum dry boiling point of 446°F. It has a higher boiling point for performance braking systems.
- DOT 5 brake fluid is silicone-based. It does not absorb water readily so has a more consistent viscosity.
- DOT 5.1 brake fluid is glycol-ether based like DOT 3 and 4 but with a higher boiling point.
Choosing the proper brake fluid type for your vehicle braking system is critical for safe operation and preventing brake failure.
Checking Brake Fluid Levels
Checking your brake fluid levels regularly is important to avoid running low. Here’s how to check the brake fluid reservoir:
Locate the reservoir – The brake fluid reservoir is a plastic translucent tank that holds the brake fluid. It is located under the hood, usually near the back of the engine bay.
Check when cold – The fluid level needs to be checked when the engine and brakes are cold, before driving it. Brake fluid expands when hot, so checking when cold will give you an accurate reading.
Look at the min/max marks – The reservoir has minimum and maximum fill lines. The fluid level should be between the MIN and MAX marks. If it is below the MIN line, you need to top it up.
Check the color – Healthy brake fluid is clear with a tint of yellow. If it is dark or murky, it could mean there is moisture contamination.
Wipe and recheck – Moisture can cling to the walls of the reservoir and provide a false reading. Wipe the reservoir with a clean cloth and recheck the level.
Refer to manual – Your vehicle’s manual will have specific instructions for checking the brake fluid on your make and model.
Effects of Low Brake Fluid
When brake fluid levels get too low, you’ll start to notice some serious effects on your vehicle’s braking performance. Here are the major effects of low brake fluid:
Loss of Braking Ability
The most obvious effect is reduced braking power. Your brakes rely on hydraulic pressure created by the brake fluid to stop your wheels from spinning. With less fluid, there is less pressure applied when you hit the brake pedal. This means it will take you longer to slow down and stop the vehicle.
Longer Stopping Distances
Due to the loss of braking force, your stopping distances will increase dramatically with low fluid. Your braking distances could easily double, sometimes more. This makes it much harder to stop in time to avoid obstacles or traffic ahead.
Brake Failure
In extreme cases of low brake fluid, such as a major leak, you may lose braking ability altogether as the fluid drops below a critical level. Total brake failure is dangerous, often resulting in crashes. Always address low fluid right away before it turns into a brake failure.
Damage to Components
Letting the brake fluid reservoir run too low allows air into the brake lines and cylinders. This leads to corrosion and damage to brake components. Pumps, cylinders, calipers, and valves can be ruined by depleted fluid. This causes expensive repairs down the road.
Symptoms of Low Brake Fluid
There are several telltale signs that your brake fluid levels may be dangerously low:
Brake pedal feels spongy/soft – One of the first symptoms you may notice is that the brake pedal feels soft or spongy when you press down on it. Healthy brakes should feel firm and responsive, so softness indicates an issue with brake pressure.
Brake pedal goes to floor – As brake fluid gets lower, you may find the brake pedal drops all the way to the floor when pressed, with little resistance. This occurs because there is insufficient fluid to apply the proper pressure.
Warning light comes on – Most cars have a brake system warning light on the dash that illuminates when fluid levels run low. Pay attention to this light and have your brakes checked if it turns on.
Leaks under car – Visually inspect the ground underneath your car where the brakes are located. Any puddles or drips likely indicate a fluid leak from the brake system.
Causes of Low Brake Fluid
There are several potential causes that can lead to low brake fluid levels in your vehicle:
Leaks
One of the most common causes of low brake fluid is a leak somewhere in the brake system. Brake fluid is designed to be in a closed system, so any leaks mean fluid is escaping and levels are dropping. Potential leak points include brake lines, calipers, wheel cylinders, and the master cylinder. Any cracks, damage, or corrosion in these components can allow fluid to leak out.
Worn Brake Pads
As your brake pads wear down over time, more space is created between the pads and brake rotors. This extra space allows calipers to extend further and the brake fluid reservoir has to compensate by releasing more fluid. Eventually this can lead to lowered fluid levels.
Age and Corrosion
Brake fluid absorbs moisture over time which eventually causes deterioration and reduces its effectiveness. The copper and aluminum components in brake systems can also corrode when exposed to moisture contaminated brake fluid. This corrosion inside the brake system leads to pitting and wear which can create new leak points. Old, contaminated brake fluid combined with corroded components is a common reason for declining brake fluid levels.
Dangers of Low Brake Fluid
Driving with low brake fluid levels can be extremely dangerous and put you and others at risk. Some of the key dangers include:
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Increased stopping distance – With low brake fluid levels, you may find it takes significantly longer for your vehicle to come to a complete stop when braking. This increased stopping distance makes it much harder to stop in an emergency.
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Complete brake failure – If your brake fluid drops below a certain level, it can lead to a complete loss of braking ability. Your brake pedal may go all the way to the floor with no braking effect when this happens.
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Accidents/injury – The increased stopping distance and potential for complete brake failure dramatically raises your risks of being involved in an accident. Collisions at high speeds can lead to severe injuries or even death. Having faulty brakes multiplies your chances of crashing into another vehicle or pedestrian.
Don’t take any chances with low brake fluid. Top it up or get professional help immediately to avoid these serious dangers and keep yourself and others safe on the road.
When to Top Up Brake Fluid
There are a few instances when you may need to top up your brake fluid:
After brake work is completed: Anytime you have work done on your brakes such as replacing brake pads or rotors, your brake fluid levels may drop as air is introduced into the system. Check and top up your brake fluid after having any brake service completed.
When the level is low: Routinely check your brake fluid according to the maintenance schedule recommended in your owner’s manual. If you notice it is low at any point, go ahead and add more. The brake fluid reservoir is typically located under the hood so check it when you are checking other fluid levels.
According to your maintenance schedule: Most vehicle manufacturer’s recommend flushing the brake fluid every 2-3 years. When it is time for this maintenance, the old fluid will be drained and the system refilled with fresh fluid. Follow the recommended schedule to keep your brake fluid fresh and at the proper level.
How to Top Up Brake Fluid
Topping up your brake fluid is a relatively simple process, but it’s important to do it properly to avoid compromising your braking system.
Here are the key steps for safely adding more brake fluid:
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Use the proper brake fluid type recommended by your vehicle manufacturer. Using the wrong fluid can damage brake system components.
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Thoroughly clean the brake fluid reservoir cap before removing it to prevent dirt or debris from entering the reservoir.
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Add new brake fluid slowly, being careful not to spill any on painted surfaces as it can damage the paint. Only add enough fluid to reach the “Full” line.
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After adding fluid, gently pump the brake pedal a few times to distribute the fluid throughout the system.
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Check carefully for any leaks around the brake lines, calipers, wheel cylinders or anywhere else in the system. Fix any leaks before driving the vehicle.
Adding brake fluid is most safely done by a professional mechanic, but you can top it off yourself between services if needed. Just be sure to use the proper fluid type and check for leaks to avoid creating bigger issues.
When to Seek Professional Help
Low brake fluid can sometimes indicate more serious issues that require professional servicing. Here are some signs you should seek help from a mechanic:
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Brake fluid leaks – Any signs of leaking brake fluid means there is a leak in the brake system. This could lead to brake failure and should be addressed immediately.
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Warning light stays on – Most vehicles have a brake warning light on the dash. If it stays illuminated even after topping up your brake fluid, there is likely an underlying issue.
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Brakes feel abnormal – Spongy, soft, or inconsistent brake pedal feel could signal problems with brake fluid flow or leaks. Don’t delay in getting it checked.
In these cases, have a professional inspect the entire brake system to identify issues and perform any needed repairs. Driving with faulty brakes can lead to dangerous situations, so never ignore signs of low brake fluid or other brake problems.
Maintaining Proper Brake Fluid
To help ensure your brake fluid levels remain adequate, follow these maintenance tips:
- Check brake fluid levels regularly – Inspect levels in the brake fluid reservoir monthly, and top up as needed. Brake fluid should be filled to the “Full” line.
- Change brake fluid per the maintenance schedule – Brake fluid absorbs moisture over time which leads to a drop in boiling point. Replace fluid every 2 years or 30,000 miles.
- Fix any leaks promptly – Wet spots near brakes indicate a leak. Have the source of the leak repaired right away to prevent brake failure.
- Use the proper brake fluid type – Check your owner’s manual for the recommended fluid specification. Using the wrong fluid can corrode brake system components.
Following these simple maintenance practices will help ensure the brake fluid in your vehicle remains in proper condition.