MISCO Digital Handheld Refractometer

Brake Fluid’s Dirty Little Secret:

DOT Standard 116 requires that DOT3 brake fluid, with no moisture content, will only boil at temperatures above 400 °F (205 °C). The brake fluid in a three to four year old car, with three to four percent water content in the brake fluid, could boil at less than 300 °F (149 °C).

Easy To Use:       

Testing brake fluid on a refractometer is simple and straightforward. Just add a drop of brake fluid from the master cylinder or wheel cylinder on the measuring surface, close the sample cover, allow a brief period for the temperature to stabilize, and press the <GO> button. The refractometer will quickly display your measurement of water content or estimated boiling point.

Refractometer for Testing Brake Fluid

Measure brake fluid water content and estimated boiling point for DOT3 and DOT4 brake fluids. 

As part of the regular maintenance interval, many automobile manufacturers recommend routine brake fluid inspection. However, there was never an easy, inexpensive means for testing it; until now. A Brake Fluid Refractometer represents the most precise field testing means available to determine the water content and estimated boiling point of automotive brake fluids.

No Brakes – The Dangers of High Water Content in Brake Fluid:

A dangerous condition exists when brake fluid boils in the braking system; it can feel like air trapped in the braking lines. In extreme cases, the driver may push the brake pedal entirely to the floor without slowing or stopping the vehicle. In colder climates, brake fluid with high water content becomes thick, causing slow pedal response or difficulty braking. Moreover, as the water content in brake fluid increases, it will become more corrosive to steel pistons and the ABS modulator.

Even New Cars Contain Water in Their Brake Fluid!

Automotive brake fluid is “Hygroscopic.” That means that it won’t take long for brake fluid to absorb moisture directly from the air, even in a sealed braking system. The Society of Automotive Engineers (SAE) conducted a study of automotive brake fluid. They found that an average one-year-old car had 2% moisture in its brake fluid. Randomly tested cars in the U.S., with an average age of eight years, showed an average water content greater than 2½%. Of these cars, 25% had a dangerously high water content of 4% or more.

The Result is Catastrophic Brake Failure!

Brake fluid with high water content has a reduced boiling point. That means that the brake fluid will boil in the wheel cylinder at a lower temperature than specified. When traveling down a steep grade, towing a trailer, or in the event, a brake pad becomes stuck against a rotor, brake fluid temperature can increase high enough to boil if it contains enough water. In the case of boiling, stepping on the brake pedal will now only compress the vapor instead of applying hydraulic force to the pad – the result is sudden brake failure.

When Should I Change my Brake Fluid?

Generally, the type of driving should influence when to change brake fluid. If the vehicle is used for towing, driving in mountainous regions, driven at high speeds or has ABS brakes, it would be best to change the fluid at 2% water content. All vehicles should have the brake fluid changed when the water exceeds 3%.

Many motor vehicle companies recommend changing brake fluid every 12 months, others recommend changing every 24 months. The amount of moisture that brake fluid absorbs depends on a number of factors including the type of fluid, humidity, type of brake hoses, condition of the seals and mileage.

Generally, brake fluid will absorb 1% or more moisture per year of service life. A two year old car will have 2-3% water in the brake fluid. 2% water reduces the boiling point of DOT3 brake fluid by approximately 135 degrees Fahrenheit (75 degrees Celsius). 2% water in DOT4 brake fluid reduces boiling point by 81 degrees Fahrenheit (45 degrees Celsius).

 

 

Condition

Water Content

Boiling Point (F)

Boiling Point (C)

DOT3

OK

Less Than 2%

Above 356

Above 180

Borderline

2% to 3%

320 to 356

160 to 180

Change

Greater than 3%

Less than 320

Less than 160


DOT3
High Temp

OK

Less Than 2%

Above 374

Above 190

Borderline

2% to 3%

320 to 374

160 to 190

Change

Greater than 3%

Less than 320

Less than 160


DOT4

OK

Less Than 2%

Above 410

Above 210

Borderline

2% to 3%

369 to 410

187 to 210

Change

Greater than 3%

Less than 320

Less than 187


Super
DOT4

OK

Less Than 2%

Above 414

Above 212

Borderline

2% to 3%

374 to 414

190 to 212

Change

Greater than 3%

Less than 374

Less than 190

Generally, brake fluid will absorb 1% or more moisture per year of service life. A two year old car will have 2-3% water in the brake fluid. 2% water reduces the boiling point of DOT3 brake fluid by approximately 135 degrees Fahrenheit (75 degrees Celsius). 2% water in DOT4 brake fluid reduces boiling point by 81 degrees Fahrenheit (45 degrees Celsius).

Pre-Configured Refractometers

Easy Order: Here are a few of the most popular Scale Combinations and Refractometer Models. If you require different programming, you can mix and match scales through the Flexible Custom Programming section below, or call customer service for assistance:

Flexible Custom Programming Options

MISCO Palm Abbe Digital Refractometers can be custom-programmed with up to 5 scales to your exact specifications. There are two easy online options to create your customized units from hundreds of measurement scales:

“Build Your Own” Tool

  1. Use the Industry, Application and Fluid filters to quickly find your scales.
  2. Click scale boxes to add scales to your device.
  3. Select Accessories
  4. Add To Cart

Order Refractometer by Scale#

  1. Browse the refractometer scale options in the dropdown tabs below and record the scale numbers you want.
  2. Type in your scale numbers on the Order by Scale# page.
  3. Select Accessories
  4. Add To Cart
Brake Fluid

Brake Fluid DOT3 % H2O

Scale# 061
UoM: % Water
Range: 0 to 6
Resolution: 0.1
Precision: 0.5

Brake Fluid DOT3 Boil °C

Scale# 166
UoM: Boiling Point °C
Range: 118 to 252
Resolution: 1
Precision: 5 ºC

Brake Fluid DOT3 Boil °F

Scale# 062
UoM: Boiling Point °F
Range: 244 to 485
Resolution: 1
Precision: 10 ºF

Brake Fluid DOT3 HT Boil °C

Scale# 167
UoM: Boiling Point °C
Range: 107 to 292
Resolution: 1
Precision: 5 ºC

Brake Fluid DOT3HT % H20

Scale# 063
UoM: % Water
Range: 0 to 6
Resolution: 0.1
Precision: 0.5

Brake Fluid DOT3HT Boil °F

Scale# 064
UoM: Boiling Point °F
Range: 225 to 558
Resolution: 1
Precision: 10 ºF

Brake Fluid DOT4 % H20

Scale# 065
UoM: % Water
Range: 0 to 6
Resolution: 0.1
Precision: 0.5

Brake Fluid DOT4 Boil °C

Scale# 066
UoM: Boiling Point °C
Range: 143 to 278
Resolution: 1
Precision: 5°C

Brake Fluid DOT4 Boil °F

Scale# 164
UoM: Boiling Point °F
Range: 288 to 532
Resolution: 1
Precision: 10 ºF

Brake Fluid DOT4+ % H20

Scale# 067
UoM: % Water
Range: 0 to 6
Resolution: 0.1
Precision: 0.5

Brake Fluid DOT4+ Boil °C

Scale# 068
UoM: Boiling Point °C
Range: 158 to 293
Resolution: 1
Precision: 6°C

Brake Fluid DOT4+ Boil °F

Scale# 165
UoM: Boiling Point °F
Range: 316 to 559
Resolution: 1
Precision: 10 ºF
Related: Battery

Sulfuric Acid % w/w

Scale# 117
UoM: % w/w
Range: 0 to 60
Resolution: 0.1
Precision: 0.1

Sulfuric Acid (D113/113°F)

Scale# 783
UoM: Specific Gravity (113°F)
Range: 1.000 to 1.399
Resolution: 0.001
Precision: 0.001

Sulfuric Acid (D131/131°F)

Scale# 784
UoM: Specific Gravity (131°F)
Range: 1.000 to 1.397
Resolution: 0.001
Precision: 0.001

Sulfuric Acid (D20/20)

Scale# 118
UoM: Specific Gravity (D20/20)
Range: 1.000 to 1.5012
Resolution: 0.001
Precision: 0.001

Sulfuric Acid (D30/30)

Scale# 832
UoM: Specific Gravity (D30/30)
Range: 1.00 to 1.491
Resolution: 0.001
Precision: 0.001

Sulfuric Acid (D50/50°F)

Scale# 780
UoM: Specific Gravity (50°F)
Range: 1.000 to 1.413
Resolution: 0.001
Precision: 0.001

Sulfuric Acid (D60/60°F)

Scale# 450
UoM: Specific Gravity (60°F)
Range: 1.000 to 1.502
Resolution: 0.001
Precision: 0.001

Sulfuric Acid (D77/77°F)

Scale# 781
UoM: Specific Gravity (77°F)
Range: 1.000 to 1.405
Resolution: 0.001
Precision: 0.001

Sulfuric Acid (D80/80°F)

Scale# 451
UoM: Specific Gravity (80°F)
Range: 1.000 to 1.496
Resolution: 0.001
Precision: 0.001

Sulfuric Acid (D95/95°F)

Scale# 782
UoM: Specific Gravity (95°F)
Range: 1.000 to 1.402
Resolution: 0.001
Precision: 0.001
Related: DEF - Diesel Exhaust Fluid

Urea % w/w

Scale# 185
UoM: % w/w
Range: 0 to 51
Resolution: 0.1
Precision: 0.1

Urea (g/cm3)

Scale# 187
UoM: Density (g/cm3)
Range: 1.000 to 1.1313
Resolution: 0.001
Precision: 0.00029

Urea (mol/Liter)

Scale# 628
UoM: Molarity (mol/Liter)
Range: 0 to 8.6
Resolution: 0.01
Precision: .02

Urea (nD20)

Scale# 629
UoM: Refractive Index (nD)
Range: 1.3330 to 1.4140
Resolution: 0.0001
Precision: .0001

Urea (ppt)

Scale# 190
UoM: Parts Per Thousands (ppt)
Range: 0 to 460
Resolution: 1
Precision: 1

Urea Freeze Point ºC

Scale# 189
UoM: Freeze Point ºC
Range: 0 to -17
Resolution: 1
Precision: 0.1

Urea Freeze Point ºF

Scale# 188
UoM: Freeze Point ºF
Range: +32 to 0
Resolution: 1
Precision: 0.1
Related: Engine Coolant

Ethylene Glycol % v/v

Scale# 011
UoM: % v/v
Range: 0 to 100
Resolution: 0.1
Precision: 0.1

Ethylene Glycol % w/w

Scale# 012
UoM: % w/w
Range: 0 to 100
Resolution: 0.1
Precision: 0.1

Ethylene Glycol (D20/20)

Scale# 015
UoM: Specific Gravity (D 20/20)
Range: 1.0000 to 1.1153
Resolution: 0.0001
Precision: 0.0001

Ethylene Glycol (g/cm3)

Scale# 379
UoM: Density (g/cm3)
Range: 0.998 to 1.113
Resolution: 0.0001
Precision: 0.0002

Ethylene Glycol Boil °C

Scale# 381
UoM: Boiling Point °C
Range: 100 to 152
Resolution: 1
Precision: 1

Ethylene Glycol Boil °F

Scale# 380
UoM: Boiling Point °F
Range: 212 to 305
Resolution: 1
Precision: 1

Ethylene Glycol Freeze °C

Scale# 014
UoM: Freeze Point ºC
Range: 0 to -59
Resolution: 1
Precision: 1

Ethylene Glycol Freeze °F

Scale# 013
UoM: Freeze Point °F
Range: +32 to -79
Resolution: 1
Precision: 2

PG Freeze °C (GEN)

Scale# 909
UoM: Freeze Point °C
Range: 0 to -51
Resolution: 1
Precision: 1

PG Freeze °F (GEN)

Scale# 908
UoM: Freeze Point °F
Range: 32 to -60
Resolution: 1
Precision: 2

Propylene Glycol % v/v

Scale# 006
UoM: % v/v
Range: 0 to 100
Resolution: 0.1
Precision: 0.1

Propylene Glycol % w/w

Scale# 007
UoM: % w/w
Range: 0 to 100
Resolution: 0.1
Precision: 0.1

Propylene Glycol % w/w (GEN)

Scale# 907
UoM: % w/w
Range: 0 to 100
Resolution: 0.1
Precision: 0.1

Propylene Glycol (D20/20)

Scale# 010
UoM: Specific Gravity (D20/20)
Range: 1.0000 - 1.0460
Resolution: 0.0001
Precision: 0.0001

Propylene Glycol Freeze °C

Scale# 009
UoM: Freeze Point ºC
Range: 0 to -51
Resolution: 1
Precision: 1

Propylene Glycol Freeze °F

Scale# 008
UoM: Freeze Point °F
Range: +32 to -60
Resolution: 1
Precision: 2
Related: Washer Fluid

Methanol % v/v <

Scale# 023
UoM: % v/v <
Range: 0 to 45
Resolution: 0.1
Precision: 0.5 to 0.8

Methanol % v/v >

Scale# 027
UoM: % v/v >
Range: 84 to 100
Resolution: 0.1
Precision: 0.5 to 0.2

Methanol % w/w <

Scale# 024
UoM: % w/w <
Range: 0 to 40
Resolution: 0.1
Precision: 0.5 to 0.8

Methanol % w/w >

Scale# 028
UoM: % w/w >
Range: 80 to 100
Resolution: 0.1
Precision: 0.4 to 0.2

Methanol (D20/20) <

Scale# 025
UoM: Specific Gravity (D20/20) <
Range: 1.000 to 0.935
Resolution: 0.001
Precision: 0.001 to 0.005

Methanol (D20/20) >

Scale# 026
UoM: Specific Gravity (D20/20) >
Range: 0.849 to 0.793
Resolution: 0.001
Precision: 0.001 to 0.005

Methanol Freeze °C

Scale# 022
UoM: Freeze Point °C
Range: 0 to -39
Resolution: 1
Precision: 0.5 to 1.7

Methanol Freeze °F

Scale# 021
UoM: Freeze Point °F
Range: +32 to -39
Resolution: 1
Precision: 1 to 3

Refractometer Platform Choices

Inline-Process Refractometer:

The above scales are also available on any MISCO inline process refractometer or concentration sensors. They are made for continuous concentration measurement of process fluids.

MISCO Handheld Digital Refractometer:

MISCO has the most extensive refractometer scale library on the planet. Don't see what you want? Browse by handheld refractometer model or by refractometer application. Or give us a call. We can help!

From our Q&A Forum

How do you know when to change DOT brake fluid?

It is generally believed that a moisture content of less than 2% is safe for most driving conditions in most parts of the U.S. Conventional wisdom says that a moisture content of 2 to 3% is marginal and that it should absolutely be changed at 3%. You should consult your vehicles owner’s manual or vehicle manufacturer for their recommendations with respect to your specific car. A car generally absorbs about 1% moisture per year of service life. Many motor vehicle companies recommend changing brake fluid every 12-months, others recommend changing every 24-months. The amount of moisture that brake fluid absorbs depends on a number of factors including the type of fluid, humidity, type of brake hoses, condition of the seals and mileage.