I recently ran out of DOT-3 brake fluid and was wondering if I could just use the DOT-4 I have instead. From what I understand, DOT-4 mixes with DOT-3 and can be used wherever DOT-3 is required. If this is the case, why is DOT-3 still made?
Dang! I meant to title the post DOT-4 instead of DOT-3…
Just go buy some of the correct fluid for your system. Not worth saving a few bucks.
DOT-4 is marginally better than DOT-3 and they do interchange. DOT-4 is slightly more expensive and has a slightly higher boiling point. DOT-4 will work in your system. DOT-5 is the stuff you want to avoid. It is silicone based, quite expensive, and fully NONCOMPATIBLE with traditional brake fluids. It is commonly used in high performance applications.
Does the can of DOT-4 say ‘good for DOT-3 applications’ or something like that? If so, I would use it. Castrol’s brake fluid is good for both: http://www.castrol.com/castrol/sectiongenericarticle.do?categoryId=9012213&contentId=7024043
We use DOT-5 in our TR6. I wanted to used it my Mustang when I put the Brembos on, but I was told it doesn’t do well with anti-lock brakes.
I think ALL the DOT-4 cans say it’s good for DOT-3 applications. From the research I did on the net, some say DOT-4 is better, some say it’s worse, others say you should change it more often than DOT-3. On top of that, I discovered that not only is there a DOT-3 and DOT-4, but there’s a DOT-5.1 that’s also compatible (not to be confused with the DOT-5 which isn’t compatible)! Then I find this from Valvoline (http://www.valvoline.com/products/brands/valvoline/dot-3-4-brake-fluid/28) that calls itself “DOT 3 & 4 Brake Fluid”. I’m more confused now than before! Argggggggggghhhhhhhh!!!
It actually costs a bit more for the DOT-4. I thought I was taking a step up to a better formulated fluid, but I think you might just be right on this one…
As long as your can says ‘compatible with DOT 3 fluid’ I think you’re fine using it, with no need to switch out fluids. I wouldn’t go the DOT 5.1 route, but that’s not what you’re wanting to do, right?
As for what you read on the web, I’d ignore folks who claim to know which one is better or worse, unless they are credible. How would somebody ‘know’ one had to be changed more often? If a manufacturer says their fluid is fully compatible, I’d take them at their word - on such a safety-related item like brake fluid they’d be opening themselves up for BIG lawsuits if it wasn’t true.
Is the DOT-4 Bottle open? If so, how long has it been open? The brake fluid absorbs moisture, and you don’t need that trouble.
Dot3, DOT-4 equals “shelf space”