dot3 or dot4 brake fluid 2001 Dakota

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Moparnutt340

Moparnutt340

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I just picked up a 2001 Dakota for a beater/work truck
It had a bad leak in the brake line so the fluid was empty. I dumped in a full bottle of Dot3 brake fluid, which was a waste because I still had no brakes anyways. Drove it home an hour away with no brakes. Thankfully its a 5 speed so downshifting to stop worked out for me.
So today I changed the brake line. I went to put fluid in it and read the cap which says Dot4 fluid only. It still has some dot3 fluid in it from the drive home.
Can the 3 and 4 be mixed or should I drain it ?
Will it do any harm if I run dot3 instead of 4?
 
You can mix dot 3 and 4 all you want but NEVER dot 5. The biggest difference between dot 3 and 4 is the dry boiling point. 4 is higher but unless you are racing or given this is a truck towing dot 3 would be fine if you rather save some money.
 
Drain it and put DOT 4 in it. The solution itself is different and it will resist to higher heat temperatures and moisture absorbency designed for the OEM brake system. better to be safe than to have your fluid start boiling and bubbling causing spongey brakes while you're on a drive.
 
charger426 said:
You can mix dot 3 and 4 all you want but NEVER dot 5. The biggest difference between dot 3 and 4 is the dry boiling point. 4 is higher but unless you are racing or given this is a truck towing dot 3 would be fine if you rather save some money.
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Flat out wrong. I run DOT 5 in everything I own, cars bikes bicycles. They're completely miscible and DOT5 won't absorb moisture causing rot from the inside out.
 
jos51700 said:
Flat out wrong. I run DOT 5 in everything I own, cars bikes bicycles. They're completely miscible and DOT5 won't absorb moisture causing rot from the inside out.
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Before you start saying someone is wrong why not provide facts? "silicone based DOT 5 is the odd one out and is not compatible with any other DOT brake fluid" (Epicbleedsolutions, 2014).

Now what you said about DOT 5 not absorbing moisture is true and thats why it is a great brake fluid. BUT you need to either have a new system or be 100% you have gotten all the old fluid out or the old fluid will react with the DOT 5 and cause poor braking performance.

References
Epicbleedsolutions. (2014). What is the Difference between DOT 4 and DOT 5.1 Brake Fluid? | Epic Bleed Solutions. Retrieved February 16, 2015, from http://www.epicbleedsolutions.com/resources/faq/difference-between-dot4-and-dot51-brake-fluid/
 
jos51700 said:
Flat out wrong. I run DOT 5 in everything I own, cars bikes bicycles. They're completely miscible and DOT5 won't absorb moisture causing rot from the inside out.
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Dot 5.1 is compatible with dot 3&4, as it is polyethylene glycol based. Dot 5 is silicone base fluid and it is not.
 
ChrisPerry said:
Dot 5.1 is compatible with dot 3&4, as it is polyethylene glycol based. Dot 5 is silicone base fluid and it is not.
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DING DING DING!!! DOT 5.1 and DOT 5 are completely different. DOT 5.1 is a new fluid type that actually performs better than DOT 3 or 4 from a wet boiling point prospective.
 
DOT5 (silicone) also has a history of being spongy (its in fake boobs, soft eh?) in non-ABS brakes. Dont know why, maybe it was a cross contamination issue. DOT3-DOT4 is fine. 5.1 is more like 3-4.
 
pishta said:
DOT5 (silicone) also has a history of being spongy (its in fake boobs, soft eh?) in non-ABS brakes. Dont know why, maybe it was a cross contamination issue. DOT3-DOT4 is fine. 5.1 is more like 3-4.
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Problem with DOT 5 is its very hard to get all the air out of the system. As we all know air in a system is what causes that spongy feelings. Just another reason why the Army wants to stop using DOT 5
 
I had a customer with a motorbike come in one day, who was having braking issues. I popped the cap and was perplexed at what i was seeing in there.I removed all that brake fluid from the system and put it in a clear glass jar.Of course I flushed his system, put fresh fluid into it etc. and he was good to go. When the customer returned for his machine I showed him what I had removed.By this time the fluid had separated into three distinct layers. The customer admitted that he had put the wrong fluid in there.
So, for sure; silicone fluid does not mix with anything else.
 
Tremendous mis-information out there. Do enough research like me, and you will understand:

1. DOT 5 is a rating and doesn't technically mean silicone fluid. When glycol fluids were finally able to meet that higher standard, they were required to be called 5.1, so as not to be confused with silicone. DOT 5.1 still absorbs moisture and eats paint.

2. Silicone and glycol fluids mix with no strange effects or chemical reactions. Many have tested this. The bottles warn not to mix because of lawyers. Of course, if you leave any glycol, that is areas that can still rust.

3. You are unlikely to notice any difference in sponginess if you use silicone. I don't. Pour it in slowly down the side of a funnel so you don't entrain air bubbles. If you drop the bottle, wait 1 day for the bubbles to come out. Don't be alarmed when the blue turns slight yellow. That is just the blue dye degrading (common). DOT 5 bottles warn not to use it in ABS systems. No internet speculators have found the reason. Is it a true issue w/ more compressibility or did manufacturers just not qualify silicone in their ABS systems (lawyers again)?

4. Weird theories out there how you can get more water damage w/ silicone since it doesn't absorb any water that drips in your reservoir. If stupid enough to let water drip in your reservoir, you shouldn't be opening the hood.

5. Synthetic brake fluid is no better. All brake fluids - glycol or silicone are synthetic and have always been.

6. Silicone does not degrade seals any more than glycol. Indeed, some 1950's British cars required silicone since glycol degraded their seals.

7. DOT 4 is very similar to DOT 3. It simply has more moisture absorbing ability, so you can go longer before flushing in new fluid. But, you still need to refresh your fluid every 2-5 yrs, depending on where you live, or risk internal rust.

8. Glycol fluid has a slightly higher boiling point than silicone when new. However, after a year or so absorbing moisture (real world), glycol has a lower boiling point. Thus, harder to meet the DOT 5 standard.

9. Silicone fluid is much more expensive and harder to find. From ads, it appears to be used in many motorcycles. Once installed, you may never need to change it since your MC and wheel cylinders will no longer rust and thus leak. It is most used by owners who don't want their trailer queen's expensive paint job ruined, but many drivers appreciate the long-term benefits. The military uses silicone since less maintenance is very valuable in distant lands. I have bought it in 1 gal cans, mil surplus, at much less than the store shelf price per qt.
 
Some very interesting info Bill. To the OP if you haven’t figured it out yet fluid topics tend to be a starting point to a lot of debate lol. All we all can offer is our opinion and what we personally do. If you decide to go with DOT5 let us know how it turns out. I've never personally used DOT because I've read many a horror story of DOT5 not working well in DOT 3/4 systems that have been changed over. But to each their own.
 
Wanna quote some sources? I'll play.


http://www.gpo.gov/fdsys/pkg/CFR-2012-title49-vol6/xml/CFR-2012-title49-vol6-sec571-116.xml

That's the DOT regs for brake fluid. read up. Not some Joe- blows opinion that you think had credibility because it's on the web.

The ONLY specification for incompatibility? Don't put hydraulic mineral oil where DOT series brake fluid is supposed to go. The rest is spec'd to REQUIRE miscibility, DOT3, 4, or 5. It doesn't have to mix to WORK. Fluid pressure doesn't mysteriously stop at boundary between fluids.

That tube of grease for the piston seals and rubber parts in your mc and caliper rebuild kits? Silicone. spec'd- for- brakes sil-glyde? Ditto. If your seals go to hell with DOT5, it's NOT the fluid!

Proof about swelling seals? When Harley Davidson switched from DOT5 to 4, the part number for the master cylinder changed but nothing else. Why? The LABEL changed on the fluid fill. Part numbers for every seal, o ring, and hose: unchanged.

Spongy fluid? Hardly. All Liquid is effectively incompressible but as you can read in the specs, DOT3, DOT5...so close you'd never know the difference. If anything, The DOT5 I'd likely less compressible than DOT3, but I can't find a spec.

Of course, when your DOT3 is full of water and boils because the piston is seized from corrosion and the pad is dragging, You might notice a bit of sponginess ;-)

Screw the hearsay. Do the research. Facts is facts, and I use DOT5 without issue and will never quit. Others have too. U.S military, Rick Ehrenbergs green brick, and more. It's standard spec for extremely cold climates.

The one problem I don't have in my cars is running DOT5.
 
Whatever floats your boat...or stops your car. As I've said before I've never had firsthand experience with DOT5 fluid. You have and seems to work for you, THATS GREAT!!! But from talking to others and from what I've read its seems that you are in the minority in having a smooth transition to DOT5 from DOT3/4.

Glad DOT5 has worked for you, I know I was looking into it for my Harley just so I didn't have to worry about the MC cover paint peeling off. But I'll just stick with DOT3, **** just bought a case of Amsoil DOT3 to go through and put fresh fluid in everything.
 
That was really the first sign that HD was getting cheap; bye bye DOT5. Now they don't even run bearings in the cam plate and the cranks aren't rebuildable. Shame.
 
I used to have really funky brakes for the first few times I used them in the spring. Calipers were really sticky for a while then would be ok. Changed rear end, reused same brakes, flushed with then filled with DOT5 and have not had sticky brakes since. That was like 15 years ago. Have not flushed or replaced anything since and fluid is still clear
 
Ill play too.
-Dot 5 in my S. Its been in there , same fluid for 15 years, in the KH 4-piston calipers which somewhere , somehow, before the internet , got a bad reputation for sticking pistons.HaH I say! Still makes back to back, multiple stops from 100+ Mph. And compressible? Hah I say! When did liquids become compressible? Is that a new thing? Never learned that in highschool. Ok, some will say its easy to get air ENTRAINED in it. Again Hah! You would have to be a newbe to have that be an issue. There may be fluid(s ) with higher boiling points. That may be an advantage for somebody. Ill take the paint protection over that anytime. If DOT5 was the only brake fluid left in the world I would rejoice cause we wouldnt be having these trivial opinions running rampant anymore. As lead tech in various bike shops, Ive been using this stuff for about 20 years already.
Use whatever. But if you dont have experience with it, please, please stop rendering an opinion.
 
Not proving and opinion when asked for one, HAHA I say lol. I think we all got away from the question that was even asked by the OP, can he use DOT3 in his factory DOT4 system...which he can.
 
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