Reason to use DOT 3 brake fluid instead of DOT 4?

[Midnite]

Some of my vehicles use DOT 3 fluid and some DOT 4. Am I mistaken to assume that DOT 4 superceded DOT 3?

Could there be a reason(s) to use #3 instead of #4?

If a vehicle specifies to use only DOT 3, can DOT 4 be substituted without harm?

 

[digitaldrifter91]

it depends...the civics 98+ can take either dot 3 or dot 4. there is a dot 5 now. i think if the bottle says that it is compadible with dot 3 then u can use dot 4. but if the manual of the car says use only dot 3 then only use dot 3. i know that dot 4 and dot 5 have better heat abilities than the dot 3. but also ur brake pump and master cylinder may not be made for a differnt fluid like dot 4. i use dot 3. there is an upgrade to dot 3 which is synthetic dot 3 that is better than the normal one but u must bleed ur brakes to get all the old stuff out.

thats what i believe.

 

[Midnite]

quote:

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Originally posted by digitaldrifter91:
... i think if the bottle says that it is compadible with dot 3 then u can use dot 4. but if the manual of the car says use only dot 3 then only use dot 3.

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Yes, I understand that 3 & 4 are compatible, and that the different cars specify the different specifications.
What I don't understand is if the two fluids are compatible, then why do some vehicles still specify DOT 3. Why also would they not say DOT 3 or DOT 4?
You comment alluding to the incompatibility of the different fluids to perhaps, seals, may be relevant - but as I've always wondered and have never been given a reason, perhaps someone here might know?

 

[OneQuartLow]

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Some of my vehicles use DOT 3 fluid and some DOT 4. Am I mistaken to assume that DOT 4 superceded DOT 3?

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Technically they're all "current" though 3 is diminishing. Price almost follows the DOT level.

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Could there be a reason(s) to use #3 instead of #4?

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No.

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If a vehicle specifies to use only DOT 3, can DOT 4 be substituted without harm?

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Yes. So far as I know, the only manuals that would call out "only DOT 3" would be those written when new formulations were in flux.

DOT 3, 4, and 5.1 fluids are compatible. (But pick one & stick with it.) All absorb water to some degree, 3 the most, so all should be exchanged every few years. Water promotes corrosion in the system, lowers the boiling point (fade), and eventually will feel "spongy." The water gets in through pores in the seals, hoses, and reservoir and of course when the reservoir is opened.

They'll take your paint right off too.

Unless track racing stick to 3 or 4. DOT 3 can eat some seals, 4 won't, so if your spec says 3 you can use either. If it says 4 stick with 4 (or 5.1). 4 has a higher boiling point than 3, absorbs less water, and is compatible with all seals. Good stuff.

DOT 5.1 has a really high boiling point to go with its price. As far as I know that's its main advantage. That's why it's numerically higher than 5 while being closer in composition to 3 & 4. (DOT levels are based on wet/dry boiling points.)

DOT 5 is silicone based & you'll end up in the river if you put it in a non-DOT 5 system. Don't do it. I've never heard anything but that you should only use it in new, empty systems. A benefit is that it doesn't absorb water (that'll come in handy in the river) so its main use is for undriven collectibles.

Like most people, I drive cars with fluid that's several years past the several year interval. Haven't had anything cut loose yet but then I'm not racing.

I will admit, every time I reply about this one I seem to buy fresh fluid & then procrastinate the actual job.

David

p.s. buy a set of speed bleeders.

 

[dkcase]

from OneQuartLow

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buy a set of speed bleeders

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Thanks for this tip. I checked out their Website.
I'll be getting some. It is sure going to beat the old way. Even with a MityVac, it's not convenient to battle with the bottle and hoses while you try to pump it up.... Looks like a definite winner.

 

[OneQuartLow]

I like them. I suppose a good vacuum pump could be better for someone with many vehicles. $7/corner adds up.

For years I used a cheapo check-valve on a hose. It worked pretty well until the hose split & I lost it in a parts box. Wastes a little more fluid but it's almost as easy as speed bleeders. Potentially less expensive, too.

David

 

[digitaldrifter91]

hehe i bled with my friend and my foot...heheh pump!! HOLD, PUMP, HOLD hhhaha. if i had an all purpose bleeder for my tranny, power steering, and brake man ill be lucky

 

[Midnite]

quote:

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Originally posted by OneQuartLow:
... the only manuals that would call out "only DOT 3" would be those written when new formulations were in flux.
...

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Thanks. This probably sums it up nicely. I realize they have different characteristics - the comment regarding seals is also a key factor - if DOT 4 is compatible with all seals and has a higher boiling point, then I assume there is no reason to not use it.

I've been using a MityVac to bleed. I appreciate the comment about struggling with hoses. It can get a little awkward and messy at times. It beats having to coordinate movements with a helper though.

With a speed bleeder, you still need someone in the car to step on the pedal. Are they trustworthy?

I'm trying to be a good boy and do my maintenance chores on time too.

 

[SteveD2]

OneQuartLow,
Another disadvantage of DOT5 silicone brake fluid is that any moisture that does get into the system does not get absorbed by the fluid, so it lays in the lowest point in the calipers and rusts.

As said, never use DOT5 brake fluid.
Ken

 

[digitaldrifter91]

so when our brakes feel spongy i should change the fluid?? well i just upgraded to ceramics and they run much hotter but dissipate heat better. latly it feels less responsive at times...i knwo the heat has to go somewhere and its in the brake fluid...i had the system flushed and re done about a year ago but maybe i should take the one in the resavor out and just put some new ones..i know it wont be as affective than bleeding the system but at leasts its there right??

 

[OneQuartLow]

quote:

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Originally posted by Midnite:
...if DOT 4 is compatible with all seals and has a higher boiling point, then I assume there is no reason to not use it.

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That's my feeling. I don't think the seal thing is that big a deal unless you have an older vehicle with natural rubber seals. Using 4 means less thinking, which is good. Still, I'd top off a 3 system with 3 until I had the chance to flush it out. I haven't heard of anyone's brakes failing after adding 4 to a 3 system but I have this thing about stopping...

quote:

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I've been using a MityVac to bleed. I appreciate the comment about struggling with hoses. It can get a little awkward and messy at times. It beats having to coordinate movements with a helper though.

With a speed bleeder, you still need someone in the car to step on the pedal. Are they trustworthy?

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Yep, just unscrew the corner, connect the hose, pump a couple times, tighten again and move to the next corner. Four trips to the driver's seat. I sometimes had to do-over with the external check valve thing but the speed bleeders are almost infallible.

Ken, yep, thanks. I deleted that during editing.

What scares me is it pooling in ABS pumps. Not a cheap fix. Can't see any reason to use 5, even on a collectible. If it's that important a vehicle I'll be all over the fluids anyway. If I can't keep it off the paint then I picked the wrong hobby.

David

 

[OneQuartLow]

quote:

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Originally posted by digitaldrifter91:
so when our brakes feel spongy i should change the fluid?? well i just upgraded to ceramics and they run much hotter but dissipate heat better. latly it feels less responsive at times...i knwo the heat has to go somewhere and its in the brake fluid...i had the system flushed and re done about a year ago ...

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No, a "spongy" description is usually caused by air in the system which compresses under braking allowing extra pedal movement. You would bleed to get it out. You could flush/bleed at the same time but that would probably be unnecessary. (And flushing is an easy way to allow air into the system.) By itself, replacing brake pads shouldn't require either. Maybe they rebuilt the calipers too?

Are they just less grabby when cold? Might be the compound choice. Ceramic pads should be pretty consistent but race/carbon-metallic compounds need to warm up a little. Double check with the vendor to find out compound type and their expected behavior.

If they've been spongy since the "flushed and re done" event then the shop probably left some air in the system. It can be tricky to bleed modern systems, especially those with ABS. If they let much air in, say when calipers or lines were removed, then it often requires a diagnostic scanner tool or wiring trick to cycle the pump & get out bubbles. You might want to talk to the shop again.

David

 

[digitaldrifter91]

well i had air in the system before and the brakes wouldnt enguage until the pedal was down to the floor...hehe thats because i pushed the caliper back. btw this is when i just installed my ceramic pads. the next day we bleeded the brakes and then it was fine. its really good in braking but its more like it lags. like as the months go on the response time when i step on the brake lessens or actually varies. my brake booster is fine and i have no leaks. this was like this when i had semi metallic pads too...we would bleed the system and it would be ok then it would go back to normal. maybe its cause its an older car. i replaced the master cylinder as well. sometimes i get good braking and sometimes i get average braking power. no matter if its hot or cold these ceramics stop now haha. maybe the fluid heated up to much and it lost its ability to do its job?? and its only been about 4 months?? maybe cause the pad is less thick than before that the braking distance of the pedal has gone down?? iono

 

[widman]

OneQuartLow has it 100%. I might add that for a lot of us outside the US there are still a lot of natural rubber parts to deal with, specially from Brazil. That means DOT 4.
The main reason people buy 3 instead of 4 is price.
Here we also have to deal with alcohol based cheap fluid that destroys everything and absorbs so much water in 6 months that the cylinders rust. But it is cheap.

 

[S2000driver]

I use Honda DOT3 fluid (It's not 3/4) brakes because it's the recommended fluid to use.

P.S. I have no problem using Honda's fluids (ATF, brake fluid, MTF, power steering, dual pump, etc.) when they are specifically specified, because they are high quality. For the amount of money I save by doing my own service, I can certainly afford using the recommended fluid in my maintenance budget. I do however use my own choice of motor oil (Mobil 1)

 

[Ken2]

DOT3, DOT4, and DOT5.1 are all polyalkylene glycol ether based brake fluids and compatible with each other. The main difference for most of us is the higher wet boiling point of the brake fluid after it has absorbed some moisture, with the higher number brake fluid having the higher wet boiling point. http://www.rpmnet.com/techart/fluid.shtml

DOT5 brake fluid is silicone based and not compatible with the other types of brake fluid. The other problem is that it is more compressible than the others, doesn't work well with ABS, and gives a spongy pedal even when fully bled.

None of these brake fluids are natural; don't fall for some "synthetic" marketing hype.

I don't know why auto makers specify DOT3. I know of no problem with mixing good DOT4 with DOT3.

Ken

 

[metroplex]

I heard DOT 4 is more hygroscopic than DOT 3 (absorbs water more readily) but has a higher boiling point, with DOT 3 being less hygroscopic and having a lower BP.

That being said, DOT 4 has a higher BP and at the worst case scenario, you'll just need to flush/bleed annually. It's not a major problem.

 

[S2000driver]

FYI-

Here's more info about the Honda fluid, if you care.

Why must I use Genuine Honda DOT 3 brake fluid?

Genuine Honda DOT 3 brake fluid is formulated to minimize water absorption under all conditions.

It has one of the highest boiling points in the industry. That's important in sustained use such as driving on hilly terrain that can heat up brake rotors and calipers.

When tested in a mass spectrometer, Honda Brake Fluid had dramatically less dissolved copper material than the leading competitors, clear proof of superior corrosion protection.

Always use Genuine Honda DOT 3 brake fluid. If it is not available, you should use only DOT 3 fluid from a sealed container as a temporary replacement. However, the use of any non-Honda brake fluid can cause corrosion and decrease the life of the system. Have the brake system flushed and refilled with Honda DOT 3 brake fluid as soon as possible.

Brake fluid marked DOT 5 is not compatible with your car's braking system and can cause extensive damage.

 

[Ken2]

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Originally posted by metroplex:
I heard DOT 4 is more hygroscopic than DOT 3 (absorbs water more readily) but has a higher boiling point, with DOT 3 being less hygroscopic and having a lower BP.

That being said, DOT 4 has a higher BP and at the worst case scenario, you'll just need to flush/bleed annually. It's not a major problem.

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Here are some of the tests and specs for brake fluid http://www.danoland.com/nsxgarage/brakes/bleed/dotspecs.html

I haven't seen anything that says that DOT4 brake fluid absorbs moisture more readily than DOT3. If you can document this, pls do.


Ken

 

[RobZ71LM7]

The differences between dot 3 and 4 are minimal. If you want a good fluid that's inexpensive try ATE Super Blue at ~$10 a liter. Dot 4 in general is not more hygroscopic-that's just a rumor. In some cases it might be in others it might not be-depends on the fluid manufacturer. You actually want a brake fluid that will have a high saturation point so that it can better protect against corrosion. The most important thing is that you flush the fluid out completely every 2 years minimum.