Dubomatic

My Mustang has possibly had dot 4 put into my dot 3 brake fluid. What are the symptoms of that effect of this happening.

tbear853

Adding Dot 4 into a Dot 3 system will cause no harm and only increases the boiling point. The two are compatible and many times you will see a bottle marked "Dopt 3/4". Dot 4 just has a higher boiling point. You can even add Dot 3 into a Dot 4 system in an emergency, but it will have a lower boiling point so good idea to do a flush / change soon.

Do not mix Dot 5 with either.

flash_xx

Nothing will happen, but good bake fluid is one of the most overlooked safety precautions, especially if you drive hard. I use Motul RBF600 and change it once a year, which is not overkill as I track the car a lot. Best fluid out there for the price.

jz

Yep, as already stated DOT 3 and 4 are only different in boiling points. DOT 5 cannot be mixed with anything else, so don't accidetally add that.