A best practice guide from Mintex on brake fluid testing, checking and everything in between.
When it comes to vehicle maintenance, monitoring the condition of brake fluid rarely makes most
drivers’ ‘to-do’ lists. This can lead to dangerous consequences for customers and a missed service opportunity for garages. Motor factors and garages play an important part in keeping drivers safe on the
road. Although most road users are au fait with the value of regular oil changes, the health of brake fluid is often ignored.
This makes the role of garages incredibly important in ensuring that a temperature test is conducted as part of a routine service. The process of testing brake fluid is straight forward and exact boiling points can be identified easily using a brake fluid tester.
Where possible, it is recommended to perform the test in the master cylinder reservoir of the car, by inserting the probe and ensuring its end sits just below the fluid level. Before performing 
the test, the equipment must be connected to the car battery, which is used to heat the brake fluid.
Process steps
As with any equipment, it’s important to find a device that is easy to use. Depending on the kit, instructions will often be shown onscreen, which takes the operator through each stage of the process. The Mintex brake fluid tester is particularly user friendly and features an LCD screen to aid usability.
As the car battery heats the brake fluid, the probe will take the temperature, which typically takes around 30 seconds. Once the test is complete, the operator is left with an accurate brake fluid temperature reading. If necessary, before and after readings can be shown to customers to demonstrate the difference in fluid levels and the importance of the test.
Although most mechanics will be familiar with performing a brake fluid test, best practice around storing the product and the different variations available may be lesser known. As brake fluid is essentially the life blood of the braking system it’s crucial that garages are fully aware of how to use it, store it and mix it.
Different variations
With regard to the different variations of brake fluids, the solution uses an American DOT system set out by the Society of Automotive Engineers and the Department of Transportation. There are four different types: DOT 3, DOT 4, DOT 5 and DOT 5.1, with the main difference between them being the temperature at which they boil. Mechanics should always use the fluid type specified by the VM to avoid mixing each variation. It is possible to mix some glycol-based fluids but never DOT 5, as this is silicone based.
The difference between glycol-based and silicone-based fluids is an important distinction to make. Glycol-based fluids are hygroscopic, which means that they naturally absorb water from the environment at normal atmospheric pressure. When brake fluid is in a vehicle, water will find its way through microscopic pores in brake hoses, seals and joints.
“The dangers associated with driving a vehicle running on old brake fluid can be life threatening, and this needs to be taken seriously by garages.”
Even when it’s on the shelf, unopened bottles can absorb moisture from the atmosphere and shouldn’t be kept on the shelf for long periods of time. It’s also essential that brake fluid is kept airtight, which is why standard bottles of brake fluid are 1.25 litres. This means that an entire bottle is used per one
brake fluid fill, to ensure that nothing is left on the shelf and susceptible to contamination.
So, how does this actually affect the brake fluid?
There are advantages and disadvantages. The upshot is that water is heav ier than brake fluid, so when it enters the product you would expect it to pool and settle in low spots and boil very easily. This isn’t the case. Due to its hydroscopic nature, water is dispersed throughout the fluid, which helps to keep the
boiling point of the brake fluid higher for longer. It also prevents internal corrosion, which wouldn’t happen if the water was allowed to pool.
The downside is that, ultimately, the presence of water within brake fluid will lower the boiling point over time. If the fluid temperature gets too low, this is extremely dangerous, and can lead to complete brake system failure.
Long life span
There is one fluid that is set apart from the rest and that’s DOT 5. This product is silicon based, which means that it is hydrophobic (as opposed to hygroscopic) and will not absorb water. As water isn’t absorbed by this fluid, DOT 5 is considered to have a very long life span and is commonly used in vehicles that need to be stored for long periods of time and are ready to go at the drop of a hat, such as
military vans and classic cars.
Importantly, although a silicone-based brake fluid doesn’t absorb water, it can still enter the system and therefore lower the boiling point. Because water can’t be absorbed by hydrophobic solutions it won’t
disperse throughout the product. Instead it will pool and settle in low spots and reduce the whole temperature of the braking system to 100˚C as well as potentially causing corrosion. This, along with the fact that silicone-based fluids can’t be mixed, is an important distinction to make and invaluable
knowledge to pass on to customers.
Standard check
Although silicone-based fluids will generally last longer, they do need changing, and it’s important to refer to the manufacturer’s recommendations on how to test and change this type of fluid.
The importance of testing brake fluid can be seen by some as inconsequential – this couldn’t be further from the truth! The dangers associated with driving a vehicle running on old brake fluid can be life threatening, and this needs to be taken seriously by garages and motor factors.
Regularly testing brake fluid not only maximises opportunities for upselling a routine service, it could potentially save a life, and this test needs to be seen as a standard check that is critical to the health of a vehicle.
