Dot 3 vs. Dot 4
 

Went to the walfart and Dot 3 is only $3.24 a liter (no liters of Dot 4 there)! while Napa wants $7.99 a liter for Dot 4. Looks like you folks think that Dot 4 is the best way to go though...

DOT 3: This brake fluid has a glycol base with additives. It is clear to amber in color. It is hygroscopic (meaning it absorbs moisture) and has a minimum dry boiling point of 401°F (205°C) minimum and a minimum wet boiling point of 284°F (140°C). It will absorb 1 to 2 percent of water per year depending on climate and operating conditions. It is used in most domestic cars and light trucks in normal driving. It does not require cleaning the system and it can be mixed with DOT 4 and DOT 5.1 without damage to the system. The problem with it is that it absorbs moisture out of the air and thereby reduces its boiling point. It can also damage the paint on a vehicle.

DOT 4: This brake fluid also has a glycol in it but the SAE J1704 specification considers it to be a borate ester base fluid. Typically in the high performance fluids, it also contains other additives. It is clear to amber in color. It is hygroscopic (meaning it absorbs moisture) and has a minimum dry boiling point is 446°F (230°C) and minimum wet boiling point of 311°F (155°C). It is used in many European cars; also for vehicles in high-altitude, towing, or highspeed braking situations, or ABS systems. It does not require cleaning the system and it can be mixed with DOT 3 without damage to the system. The problem with it is that it absorbs moisture out of the air and thereby reducing its boiling point, however it absorbs moisture at a rate slower than DOT 3. It can also damage the paint on a vehicle.

All brake fluids can damage the paint.

Which one is the right one for your car? I'll bet it's Dot3; which means, you buy that one.

Read your brake fluid cap. I'll bet yours says DOT 4 only, just like mine does. Do you really want to cheap out a few dollars on something as important as the braking system?

with the 123's solid rotors, I would opt for dot 4 or 5.1 to give as large an edge as possible. heat is the killer, so the highest boiling point the better...

Go with what the vehicle calls for. Don't be penny wise, pound foolish.

When it doubt get DOT4, thats what most MB's call for.

I don't know what Walmart or NAPA sells brake fluid for since I shop at neither. I buy it from Phil, forget what I pay I think $10-$11 a quart.

Never forget the obvious. :rolleyes:

Mine says Dot 4 and that's what's going in.

The 77 240D calls for Dot4, so that's what it gets. We just replaced the fluid with ATE Super Blue last weekend. I've used it in my car since I bought it and have been very happy.

DOT3 and DOT4 are mixable. DOT4 has a Higher boiling point due to chemical additives. DOT5 is Silicon Base, and will not blend. but it has an even higher boiling point.

I use this
http://pac1.net/corvette.california/...ndums/067d.JPG

Looking at the boiling temps of the DOT 3 and DOT 4 I have in my garage, the only big difference was the wet boiling point. With a flush every 2 years I couldn't see the fluid getting super wet. But I will agree with others... don't cheap out on your brakes. They're your most important safety system.

Something I would do is if your car hasn't had a flush in a really long time, flush the system with some DOT 3, then a week later come back with some DOT 4. No need to use the more expensive DOT 4 just to blow the crap out of the system. And any leftover moisture will absorb into the DOT 3, and will be removed when you replace it with 4.

-Jason

You can swap DOT4 in the place of DOT3 when flushing the brakes but they should not be mixed together if possible (When topping up or bleeding brakes, for example.)

FWIW, I use the SynPower brake fluid as well.