DOT 4 brake fluid

[BigDick]

Just put new pads all around, it this dot 4 stuff ok to use? "good for all dot 3 & 4 brake systems" and "compatible with all conventional brake fluids" "recommended for all ABS, disc, and drum brake systems. . . " "meets or exceeds dot 3 and dot 4 specifications" The autozone guys said it'd be ok to use. Now i'm asking the experts.

[oldyam80sg]

I would think that you could use it-if you don't mix it.Flush system and then you could add the Dot 4.

[Ivan]

DOT 3 and $ are different blends of a caster oil and alcohol mix. They are compatible with most all automotive and powersports brake systems.

DOT 5 is a silicone based fluid that I have never seen in actual use. Might be for the space shuttle or something. Anyway, it is not good to the rubber parts in the typical brake system, so don't use it, or ATF, or motor oil, or gasoline, or deepfryer grease, or hair gel. All of which I have cleaned out of brake systems.

[oldyam80sg]

Was told a while ago not to mix.

[DGXSER]

Look at this tech tip:

There is a tech-tip or an old thread or something in here about

it would appear that 3 and 4 are for all practical purposes one and the same. It is 5 you do NOT want to mix with 3 or 4.

[oldyam80sg]

Do what you want to but you can just as well buy Dot 3 and Dot 4 fluid.if you run out of one why not buy the same stuff?

[BigDick]

From the way that reads I should drain the dot 3 completely before adding the dot 4. Do I just take off my master cylinder caps and crack the bleed screws to let the 3 drain out? then close the screws and add 4 and do the bleed process?

[dbeardslee]

I've got Dot 4 in mine, and I just pulled it through with a power bleeder until I was sure I had nothing but clean fluid in the lines. It's been working fine for the last 2 years.

[fredintoon]

Just put new pads all around, it this dot 4 stuff ok to use? "good for all dot 3 & 4 brake systems" and "compatible with all conventional brake fluids" "recommended for all ABS, disc, and drum brake systems. . . " "meets or exceeds dot 3 and dot 4 specifications" The autozone guys said it'd be ok to use. Now i'm asking the experts.

Hi BigDick,
DOT4 has a little better maximum temperature rating than DOT3.
They will mix together just fine.
The stuff you got is a hybrid that's good for either and will mix with both.
Presumably you are taking the opportunity to change the brake fluid for new stuff anyway?
So yeah, there's no need to get hysterical about squeaky-cleaning out the old stuff.
OTOH, DOT5 has a completely different chemistry that does NOT mix with DOT3 or DOT4. DOT5 was formulated for Harley guys because it don't attack paint.

[XJOK2PLAY]

Hey BD....

From the way that reads I should drain the dot 3 completely before adding the dot 4. Do I just take off my master cylinder caps and crack the bleed screws to let the 3 drain out? then close the screws and add 4 and do the bleed process?

Back in the day, I was an ASE Fleet Mechanic. What I've been told in the past in the Wagner Brake seminars I attended concurs with this article. Dot 4 just has a little bit more "antifreeze" (glycol) in it than Dot 3, so different boiling points... (Dot4 being higher.) It's when you mix 3 & 4 you actually get a reduction in boiling point BELOW Dot 3. Not a huge problem in most cases, unless ya stand on the brakes repeatedly in the twisties for about an hour or so... or you're in a truck pulling a heavy trailer, downhill. You might see some fade if the fluid got that hot. If it were me, I'd just get some Dot 3, and save all the draining, bleeding, and other potential problems, unless you're fighting a particular problem that needs the higher boiling point. Just my 2 cents, though... but then I've always been on the lazy side of trouble... (HEHE)

[Just In Case]

From memory, DOT 5 is a silicone based fluid. It won't absorb water like 3/4/5.1, but has other issues and I think the only users are the US Army.

DOT 5.1 is a similar product to 3/4 and can be mixed without immediate issues if that's all that is available.

[BigDick]

... but then I've always been on the lazy side of trouble... (HEHE)

ditto here. . .


Thanks everyone for all the great info, hopefully this thread helped someone else also. I'll take the 4 back to auto zone today and get me the 3.