DOT 3 vs DOT 4 brake fluid?
Thread Starter
Team Owner
Joined: Apr 2001
Posts: 36,453
Likes: 2
From: Overwhelmed as one would be, placed in my position.... DFW, TX
St. Jude Donor '05
DOT 3 vs DOT 4 brake fluid?
Ok, I made the mistake of buying DOT 4 brake fluid. Stupid, stupid mistake as I nearly always check, but I was in a hurry.
I used the whole bottle.
The bottle says it's compatable with all DOT 3 and DOT 4 fluids, so I don't know how bad I screwed up. I know DOT 5 is bad stuff, but what the heck is the difference between 3 and 4 and do I need to bleed all this crap out?
I used the whole bottle.
The bottle says it's compatable with all DOT 3 and DOT 4 fluids, so I don't know how bad I screwed up. I know DOT 5 is bad stuff, but what the heck is the difference between 3 and 4 and do I need to bleed all this crap out?
Burning Brakes
Joined: Dec 2004
Posts: 1,234
Likes: 2
From: New Jersey
There is no difference except in the temperature ratings.
Just like motor oil has different ratings.
DOT3 flows better when cold and DOT4 holds up better under high heat.
You have nothing to be worried about, you've done nothing wrong, unless you drive around in -30 degree temps a lot.
I use DOT4 exclusively since it never gets cold enough here to worry about it.
Just like motor oil has different ratings.
DOT3 flows better when cold and DOT4 holds up better under high heat.
You have nothing to be worried about, you've done nothing wrong, unless you drive around in -30 degree temps a lot.
I use DOT4 exclusively since it never gets cold enough here to worry about it.
Last edited by Mighty-Mouse; Jan 18, 2005 at 10:06 AM.
Le Mans Master
Joined: Dec 2000
Posts: 9,910
Likes: 1,858
From: Hot Springs AR
You didn't screw up; in fact, the Valvoline Syntec fluid I use is described as DOT 3/4. Like you, I know that DOT 5 is non-compatible, but what about the compatibility between DOT 3 or 4 and DOT 5.1? 
Thanks, and have a good one,
Mike
Thanks, and have a good one,
Mike
Burning Brakes
Joined: Dec 2004
Posts: 1,234
Likes: 2
From: New Jersey
Originally Posted by VetteDrmr
You didn't screw up; in fact, the Valvoline Syntec fluid I use is described as DOT 3/4. Like you, I know that DOT 5 is non-compatible, but what about the compatibility between DOT 3 or 4 and DOT 5.1?
Thanks, and have a good one,
Mike
Thanks, and have a good one,
Mike
DOT 3 and DOT 4 are completely compatible and you can even mix the 2 with no issues what so ever.
DOT5.1 is OK. This brake fluid has a borate ester base, just like DOT4. It is used in severe-duty vehicles such as fleets and delivery trucks, towing vehicles, and racecars.
It can be mixed with DOT 3 or DOT 4 without damage to the system.
It maintains higher boiling point than DOT 3 or DOT 4 fluids due to its higher borate ester content. It is excellent for severe duty applications. The problem with it is that it costs more than other fluids and there is limited availability. It also absorbs moisture out of the air at 3 times the rate of DOT3 or DOT4 and thereby reduces its boiling point. It can also damage the paint on a vehicle.
DOT 5 is a silicone based fluid and silicone eats the seals in the system causing leaks and lose of hydraulic pressure. Leave silicone to the military.
Last edited by Mighty-Mouse; Jan 18, 2005 at 01:58 PM.
