Brake Fluid

srt20 wrote:
All DOT 3, DOT 4, and DOT 5.1 is synthetic. Some brands just like to advertise it more, but they are all synthetic. So go ahead and mix any of those combos you want.

DOT 5 is silicone brake fluid and is NOT compatible with any of the other brake fluids.

^this
Do not use DOT 5, it causes more problems than its worth.

rgatijnet1 wrote:

Tim Nowicki wrote:
OP asked about synthetic brake fluid being added to his unknown type. NOBODY answered his question. I was under the impression synthetic brake fluid and regular brake fluid can't be mixed. True or not true? thanks

The answer was given a couple of times....flush the system if you do not know what is in it. Guessing on what will mix or not is impossible if you do not know one of the fluid types. Some fluids will mix and some will not. It is too big of a gamble to add any type of fluid if you don't know what is in there now.

Doesnt matter if you flush it or not if you dont know what type fluid the manufacturer specified

All brake fluids re synthetic. The main difference is 5.0 is a silicone based fluid that is not compatible with the 3.xx and the 4.xx fluids. 5.0 isn't used in anything other than high performance vehicles.

You can't flush the system and switch to 5.0 because it isn't compatible with the rubber components in your system. If it's been more than 2 years since your brake system has been flushed I would flush it with DOT 4.0 brake fluid. If the system doesn't need to be flushed you can add either DOT 3.0 or 4.0 fluid. I would opt for the 4.0 since it has a higher boiling point and can be mixed with 3.0 with no ill effects. DOT 3.0 is considered obsolete and has been replaced by DOT 4.0

To me it would be a poor choice to use DOT5.0 in any braking system where the vehicle potentially sets for long periods of time. First of all it is not compatible with the rubber components in most master cylinders or brake cylinders. It can cause the rubber to swell or leak past it. Not being hygroscopic any water that enters the system will gravitate to the low points. It will sit there and start to rust any steel components like brake lines or calipers. If the weather is cold enough for water to freeze any water in the system will turn to ice. The last thing you want is a rusted through brake line, ice blocking the line, or a caliper literally frozen and inoperable.

It was originally developed for race cars that need a higher boiling point. It later was introduced to several high performance production vehicles. I am not aware of any motorhome chassis manufacturers that use it, or claim to have components that it's compatible with.

srt20 wrote:
All DOT 3, DOT 4, and DOT 5.1 is synthetic. Some brands just like to advertise it more, but they are all synthetic. So go ahead and mix any of those combos you want.

DOT 5 is silicone brake fluid and is NOT compatible with any of the other brake fluids.

As mentioned, if you have DOT 5 in the system, you cannot mix it with other fluids. DOT 5 fluid is used in racing cars, antique automobiles, Classic cars, and SOME motor homes that sit a lot because it does NOT absorb moisture and has a high boiling point, which is why it is preferred in certain applications. SOME motor home owners on this forum have said that they use it and it will work fine if the system is completely flushed to remove all traces of the old fluid. Apparently the OP did not know what he had in his system now so to recommend just adding any fluid is not the safest solution.
DOT 5 fluid is NOT to be confused with DOT 5.1 fluid that can be mixed. So, without knowing for sure, you take your chances.
SOME ABS systems do not work well with DOT 5.

Now there is the answer to the question. I was confusing the word synthetic with the word silicone. thank you

All DOT 3, DOT 4, and DOT 5.1 is synthetic. Some brands just like to advertise it more, but they are all synthetic. So go ahead and mix any of those combos you want.

DOT 5 is silicone brake fluid and is NOT compatible with any of the other brake fluids.

Tim Nowicki wrote:
OP asked about synthetic brake fluid being added to his unknown type. NOBODY answered his question. I was under the impression synthetic brake fluid and regular brake fluid can't be mixed. True or not true? thanks

The answer was given a couple of times....flush the system if you do not know what is in it. Guessing on what will mix or not is impossible if you do not know one of the fluid types. Some fluids will mix and some will not. It is too big of a gamble to add any type of fluid if you don't know what is in there now.

OP asked about synthetic brake fluid being added to his unknown type. NOBODY answered his question. I was under the impression synthetic brake fluid and regular brake fluid can't be mixed. True or not true? thanks

Bottom line:

New brake fluid boils about 500 degrees F.

Hydrated brake fluid (i.e. older fluid) boils at 284 degrees F.

Any questions????

Brake Fluid maintenance is of course an important safety area. Low pressure = low or no braking = danger:)!

Synth's do help avoid on moisture build up, very important to avoid moistire, as hot brakes can cause 'steaming' old non moisture contaminated brake fluids, and steaming = loss of pressure.

I agree that getting the system checked out, and if due, fluid replaced, is a good idea. If you do some Google search, you can find some higher quality certified fluids that have superior properties. Worth paying a bit extra for these fluids, as they can give you a safety edge on long down hills heat potential build up runs...

Best of luck, have fun, be safe,
Smitty