Brake Fluid Health Check Service

[Medved_77]

The owners manual states under 'Service Intervals':

• Brake fluid health check every 2 years (replace if necessary) or, if the vehicle is used for towing, replace the brake fluid every 2 years.

My car is almost 3 years old so figured I should get this done. Reading further on in the maintenance section:

So the steps to "health check" the brake fluid appear confusing. "Do not top up your brake fluid" yet here's 4 steps detailing how to top up your brake fluid...

Thought I should at least check the levels and check for moisture in the brake fluid. I bought a cheap brake fluid tester from Amazon, the Duoyi DY23B - other more well-known brands are surely available:

Removed the service cover in the frunk to reveal the brake fluid reservoir. DOT3 as clearly marked on the lid. Level of fluid looked fine.

I cleaned the cap before removing it to avoid debris falling into the reservoir. Turned on the device and set to DOT3. Put the probe (also cleaned first) into the reservoir:

Reading was 1.5%. Over 3% will give you a warning and suggests it's time to change your brake fluid.

Replaced cap, wiped probe, replaced service cover. 5 min job and done for another two years.

Note: This is testing for moisture in the brake fluid. The paper type test strips check for corrosion from the brake lines. I haven't tested for this yet.

 

[M109Rider]

Love this post. Thanks. !
Mine is 4.5 years old, and I’m worried about my fluid also.
May pick one of these up as well from Amazon.
Is corrosion an issue. ? I’m asking, not questioning.
The lines are either rubber or stainless I thought.
Again, thanks for the post. !

Edit Did a bit of checking. There are some very negative reviews for these types of testers on Amazon. )
Seems some read the same even in water. It may be that the unit either works, or it doesn’t. Maybe you have one that works, because many that claimed it didn’t, read 2.5% regardless of how new the fluid was or wet it was.
Now I’m second guessing getting one.

Anyone know if these test strip type products are reliable ?

 

[Medved_77]

Edit Did a bit of checking. There are some very negative reviews for these types of testers on Amazon. )
Seems some read the same even in water. It may be that the unit either works, or it doesn’t. Maybe you have one that works, because many that claimed it didn’t, read 2.5% regardless of how new the fluid was or wet it was.
Now I’m second guessing getting one

I'm out at the moment but can do another test with water, also have some old brake fluid lying about.

Didn't think of having a control. Good point!

 

[GlynG]

Now perhaps its just my cynical nature but - the brake fluid recommendations to replace fluid every two years is just another method of upselling - like the phoney Hydrogen cleaning of ICE - (they inject steam into the air intake - Its just boiled water the "Hydrogen" reference is the H of H2o)

Brakes on a car are pretty important and therefore a splendid way to create fear and encourage a customer to pay to ensure safety by intimating a failure to change fluid could result in disaster and brakes failing - ITS ALL TOSH.
Do people understand why fluid needs to be changed? For those of you that know - no need to read more, for those that want to know read on.

Brake fluid is Hygroscopic (Its absorbs moisture) moisture is water.
The boiling point of brake fluid is around 300 degrees C
Boiling point of water is 100 degrees C (For the pedantics the boiling point is measured at sea level, the higher you go the boiling point lowers)

A typical vehicle brake system has just one tiny hole in it - its on the brake fluid reservour cap, this lets air in as the fluid level drops otherwise you would have a vacuum, the level drops as the brake pads wear as more fluid is stored within the calliper pistons to take up the space left by pad wear. (Fit new pads and push back the pistons and the reservour will return to the "full" level again (only other reason fluid level drops is a leak)

That tiny hole does allow moisture to come into contact with the brake fluid stored in the reservour and in theory can sufficiently contaminate fluid to a point it can affect the performance of your brakes - in practice its a different story.

When you brake, the braking systems generates heat - a lot of it, If brake fluid is heavily contaminated with moisture that moisture will start to boil and create a pocket of steam, given the fact a gas can be compressed and a liquid cant - that pocket of steam will reduce the force the braking system can apply to the callipers and you get a spongy feeling brake pedal, reduced braking performance and it can affect one or more wheels - so an imbalance in the application of the brakes.
To get to the stage of boiling moisture there has to be an unusual amount of heavy braking or a very sustained amount like going down a very long gradient and using the brakes to keep the speed down - or perhaps track use of the car with frequent very heavy braking.
The amount of moisture content has to be quite significant to achieve that and the experts in braking technology indicate to ensure this cannot happen they say to change the fluid if the concentration exceeds 3%.

The very cheap testers (under £15) I would avoid, but the £20 to £30 mark testers are accurate enough and indeed many professionals use exactly that same equipment in garages to determine the the state of the fluid, Its obviously in their interest to recommend a fluid change if they get even a 1% reading and telling you, you have contaminated fluid and it wouldn't exactly be telling a lie.
For the average motorist 3% is perfectly safe and tests I have done on vehicles at 8 years old have never topped 2% (many years ago I did do a test on a 25 year old vehicle that hadn't been used for 15 years (old Girling system) - that did give a full reading on the meter - in excess of 5%

I'm not advocating people ignore brake fluid changes because my experience is based obviously in my location - The weather and humidity levels vary all over the world - your location and proximity to the sea, waterways, lakes etc all have an effect - so for some, fluid changes come earlier than others, my personal view is no one needs a fluid change on a vehicle less than 4 years for normal everyday use, in short don't be panicked into accepting a fluid change without getting quotes from others- its not impending disaster - ask them what the reading was percentage wise - bet they don't tell you.

I did watch a very reputable Independent Porsche garage carry out a fluid change on a 911, One in the car pumping the pedal the other at the callipers bleeding the fluid through (Old fashioned way now of doing it as many use vacuum or pressure systems and one man/woman job) but it was 2 pumps of the pedal on each calliper nipple (two nipples to each calliper) which wouldn't have been enough to completely change the fluid in the system - so be aware the value of a fluid change is only as good as the persons diligence doing the job and we are aware some garages are a bit dodgy.

If you do decide to purchase a tester then to ensure its working fine test it three times, on your car, test it on a old car that hasn't had brake work done in years, and final test of brand new fluid - if you get different readings you can have some degree of confidence its working reasonably fine.

 

[Medved_77]

Maybe you have one that works, because many that claimed it didn’t, read 2.5% regardless of how new the fluid was or wet it was.

Didn't have any other brake fluid available to test unfortunately but got a red warning and a lot of beeping when testing with tap water.

 

[M109Rider]

Now perhaps its just my cynical nature but - the brake fluid recommendations to replace fluid every two years is just another method of upselling - like the phoney Hydrogen cleaning of ICE - (they inject steam into the air intake - Its just boiled water the "Hydrogen" reference is the H of H2o)

Brakes on a car are pretty important and therefore a splendid way to create fear and encourage a customer to pay to ensure safety by intimating a failure to change fluid could result in disaster and brakes failing - ITS ALL TOSH.
Do people understand why fluid needs to be changed? For those of you that know - no need to read more, for those that want to know read on.

Brake fluid is Hygroscopic (Its absorbs moisture) moisture is water.
The boiling point of brake fluid is around 300 degrees C
Boiling point of water is 100 degrees C (For the pedantics the boiling point is measured at sea level, the higher you go the boiling point lowers)

A typical vehicle brake system has just one tiny hole in it - its on the brake fluid reservour cap, this lets air in as the fluid level drops otherwise you would have a vacuum, the level drops as the brake pads wear as more fluid is stored within the calliper pistons to take up the space left by pad wear. (Fit new pads and push back the pistons and the reservour will return to the "full" level again (only other reason fluid level drops is a leak)

That tiny hole does allow moisture to come into contact with the brake fluid stored in the reservour and in theory can sufficiently contaminate fluid to a point it can affect the performance of your brakes - in practice its a different story.

When you brake, the braking systems generates heat - a lot of it, If brake fluid is heavily contaminated with moisture that moisture will start to boil and create a pocket of steam, given the fact a gas can be compressed and a liquid cant - that pocket of steam will reduce the force the braking system can apply to the callipers and you get a spongy feeling brake pedal, reduced braking performance and it can affect one or more wheels - so an imbalance in the application of the brakes.
To get to the stage of boiling moisture there has to be an unusual amount of heavy braking or a very sustained amount like going down a very long gradient and using the brakes to keep the speed down - or perhaps track use of the car with frequent very heavy braking.
The amount of moisture content has to be quite significant to achieve that and the experts in braking technology indicate to ensure this cannot happen they say to change the fluid if the concentration exceeds 3%.

The very cheap testers (under £15) I would avoid, but the £20 to £30 mark testers are accurate enough and indeed many professionals use exactly that same equipment in garages to determine the the state of the fluid, Its obviously in their interest to recommend a fluid change if they get even a 1% reading and telling you, you have contaminated fluid and it wouldn't exactly be telling a lie.
For the average motorist 3% is perfectly safe and tests I have done on vehicles at 8 years old have never topped 2% (many years ago I did do a test on a 25 year old vehicle that hadn't been used for 15 years (old Girling system) - that did give a full reading on the meter - in excess of 5%

I'm not advocating people ignore brake fluid changes because my experience is based obviously in my location - The weather and humidity levels vary all over the world - your location and proximity to the sea, waterways, lakes etc all have an effect - so for some, fluid changes come earlier than others, my personal view is no one needs a fluid change on a vehicle less than 4 years for normal everyday use, in short don't be panicked into accepting a fluid change without getting quotes from others- its not impending disaster - ask them what the reading was percentage wise - bet they don't tell you.

I did watch a very reputable Independent Porsche garage carry out a fluid change on a 911, One in the car pumping the pedal the other at the callipers bleeding the fluid through (Old fashioned way now of doing it as many use vacuum or pressure systems and one man/woman job) but it was 2 pumps of the pedal on each calliper nipple (two nipples to each calliper) which wouldn't have been enough to completely change the fluid in the system - so be aware the value of a fluid change is only as good as the persons diligence doing the job and we are aware some garages are a bit dodgy.

If you do decide to purchase a tester then to ensure its working fine test it three times, on your car, test it on a old car that hasn't had brake work done in years, and final test of brand new fluid - if you get different readings you can have some degree of confidence its working reasonably fine.

Thanks for the detailed info on this topic. !
I likely will now purchase one of these units. I’ll just check that it’s working properly with some controls.
I’ve had my model 3 for 4.5 years now.
Our other one has one 10k on it. I have to say, hers seems to have a stiffer brake feel. Nothing that bothers or worries me, but just makes me want to double check the moisture level.
Thanks again for the detailed post.

 

[M109Rider]

Didn't have any other brake fluid available to test unfortunately but got a red warning and a lot of beeping when testing with tap water.

View attachment 911535

That’s a good sign.

 

[GlynG]

Medveds tester is the type to go for, there are a few manufacturers doing the same thing.

 

[vickh]

Does TSLA ranger do this check too?

 

[init6]

Does TSLA ranger do this check too?

If the Az in your location is Arizona, it may be better to ask on a US part of the forum. Activities carried out by UK&I rangers may differ from the US.

 

[Fursty Ferret]

I also wouldn’t bother with changing the brake fluid unless someone else is paying. And even then I think the risk of someone screwing up is probably higher than doing nothing. The Tesla can do about 75kW of regenerative braking, which is heat that isn’t going into the brakes, so they should never get hot enough to be an issue.

 

[KalJoMoS]

When I asked to change brake oil on my 6y old Model S last year, the service was very reluctant to agree as they insisted to keep an aye on the moisture level only. I managed to push it on and they did changed it, although it took me three consistent letters to service manager. They just owed me some service checks as previous visits had not been as should, politely saying. Sorry, not an islander, just a point from the main land.