I took my car to my Ford dealer for a brake system flush. To my amazement, the invoice showed that DOT 4 was used, while the Owner's Guide says to use DOT 3. I asked if they had any data from Ford Motor Company showing that DOT 4 was okay to use. They did not, so they did the job over, using DOT 3.

The dealer said they had switched over to DOT 4 unless the customer requested something else. Is DOT 4 okay for our cars? I read some data on the Internet that it was not necessarily okay to switch from DOT 3 to DOT 4 because there were chemicals in DOT 4 that could damage the braking system of a car designed only for DOT 3.

I have no idea whether our cars have brake hoses, etc., which could be damaged by the chemicals used in DOT 4. Anybody here know?

 

As I understand it you are not to mix DOT3 & DOT4, but if they did a proper flush of the system it won't hurt anything and provides protection from boiling in heavy braking (like a road course race track or extremely spirited driving on curvy roads.

 

I'm running DOT4. It was after upgrading my front brakes to Brembos. Flushed the system myself.

 

the only difference between the 2 is boiling point, dot 4 is higher, they can be mixed, the only one that doesnt mix is dot5 that is silicone based


Boiling point ranges [2]
Dry boiling point Wet boiling point
DOT 3 205 °C (401 °F) 140 °C (284 °F)
DOT 4 230 °C (446 °F) 155 °C (311 °F)
DOT 5 260 °C (500 °F) 180 °C (356 °F)
DOT 5.1 260 °C (500 °F) 180 °C (356 °F)
DOT 4, like DOT 3 and DOT 5.1, is a polyglycol ether-based fluid

 

^^^This. Also, it is important to be aware the DOT 4 fluid is backward compatible but the DOT 3 is not forward compatible. That is, if your car requires DOT 3 then the DOT 4 is simply a higher temp upgrade. If your car requires DOT 4, then the use of DOT 3 fluid is NOT a good idea. If you do use DOT 3 in a DOT 4 requirement then you probably should flush your system.

 

Never use dot 5 in our systems. Dot 4 needs to be flushed once a year with normal driving. You can use dot 5.1 also and that requires a flush every 2 years.

 

^^^^yes, dot 5 silicone based fluid will aerate and is not recommended in any ABS system. it is however a great fluid to use in classic applications that dont have ABS, due to its ability of keeping rubber components soft and pliable

 

Thanks to all of you who replied. I have done some more Internet searching, and this is what I think is correct.

At least some of the later model S197 cars and perhaps some earlier model performance models came from the factory with DOT 4, and the owner's guide accompanying the car states that DOT 4 is the correct fluid to use. If DOT 4 is specified, you should not use DOT 3.

If the car came from the factory with DOT 3 and that is what the owner's guide says to use, you can damage the brake hoses, seals, and fittings by using DOT 4 because DOT 4 contains certain chemicals that can damage brake systems that were designed only for DOT 3.

As an aside, a lot of drivers rate Motorcraft High Performance DOT 3 as withstanding high heat better than most other DOT 3 fluids that are available.

 

DOT 4 is a great upgrade if you ever drive your car on a track at all. I think you should use DOT 4 for your car no matter what because it is a superior fluid to DOT3. Yes you have to flush it every year, but it's not very difficult to do and is just a part of car maintenance. I have had zero issues with seals or hoses being damaged going from motorcraft DOT3 to Motul 600 DOT 4. I've been using that fluid for the past two years with quarterly re-bleeds and annual full brake flushes. I personally would have kept the DOT 4 in since it won't cause any damage to a mustang's brake system.

 

dot 4 will not damage a dot 3 system......thats complete balderdash