This might be a silly question to some, but I never really understood the difference. Can someone tell me? I do know that our car's only take DOT 3, but what will happen if I put in some DOT 4?
the short answer is: nothing will happen. The difference between the two is that DOT 4 has a higher boiling point, so you will not be as likely to have your brakes fade due to overheating in racing (open track or auto-x) or mountain driving. if you overheat the fluid and it boils, air bubbles will form in the lines, causing brake fade (squishy pedal) and in extreme cases your brakes might fail completely. DOT 3 and DOT 4 are both made with the same base fluid, but there are additives in the 4 that raise the boiling point.
Although mixing the two should not cause any adverse effects, it is generally reccomended that you dont mix the two. I have DOT 4 in mine with no probs. When i put it in, i pushed about three bottles through to make sure all of the DOT 3 was out.
there is also DOT 5, which is basically reserved for full race use, and it CAN NOT be mixed with DOT 3 or 4, as it is a different base fluid (silicone base i think). you would probably have to change out most of the components, or at least to a complete system flush to use it.
If you are not auto-xing on a regular basis, then dont even worry about it. DOT 3 will be fine for 90% of us.
Whew! sorry for writing a book, but I was on a roll! Hope this answers your question!
Oh I see. Thanks for the reply. I've always thought that DOT 4 was a special type of fluid that is only used in more expensive cars with fancy brake systems. So pretty much it's okay to use in ours too. Wouldn't it be better to have DOT 4 instead of DOT 3 anyways even though you don't drive hard or race or whatever? Like you said, it has a higher boiling point therefore reduces brake fade and overheating. It should save us money in the future to have good fluid to begin with and not have to worry about overheating and damaging any brake components in the future.
it seriously is not worth the trouble or expense to change to DOT 4 unless you NEED to. For normal everyday driving, it has little advantage unless you happen to live in the mountains or regularly slam on your brakes for no reason.
Also, there is no real "wear and tear" difference between the two. Since they are basically made of the same stuff, neither one will extend the life of your brake components, or lessen it for that matter.