DOT 4/5 fluid question

[Guest bastaad525]

Hey all... still considering replacing my brake fluid with DOT 4 or DOT 5 fluid.

 

 

I seem to remember reading somewhere though that going with a higher DOT number will have some effect on the feel of the pedal... wondering exactly what it does?

 

 

Also, someone mentioned Ford Motorcraft fluid... is that DOT 4 or 5?

 

 

What are the good brands and places to get DOT 4 or 5? Autozone doesn't carry any.

[jt1]

If the higher dot fluid affects pedal feel it will be very little if at all. The main advantage is higher boiling points for track use.

 

Valvoline Syntech is a dot 4 fluid with pretty good boiling point, and it's 4.99 a quart at autozombie, so you can bleed it regularly without breaking the bank. For street use, you shouldn't have to bleed them much, maybe once a year.

 

John

[skipzoomie]

I've changed all of my cars to Dot 5. It's the silicone fluid. It gives no different pedal feel. The biggest advantage is that it is not hydroscopic. That is it does not absorb moisture from the atmosphere. If you have noticed all of the mud that forms in older master cylinders and wheel cylinders then you have seen the results of moisture in the brake fluid. All of this contamination is what destroys the brake system components. Years ago I had a Plymouth Volare, (no laughing, it was one of the most reliable cars I've owned), I changed the fluid to Dot 5 and for 10 years never had a brake problem other than just normal brake disc and shoe replacement. Try it, you'll like it.

[2126]

DOT 5 fluid may not absorb moisture but this does not stop moisture from getting into a brake system. With the DOT 5, moisture will pool in the low areas and cause the corrosion there. Also, DOT 5 has a less than desirable expansion rate than the DOT 3, 4, and 5.1 fluids. It's common knowledge that DOT 5 is good for non-performance type cars, like vintage restorations and commercial trucks (the military uses this stuff in their trucks). I don't believe you will see DOT 5 used in any race car applications due to it's expansion rate. One good thing about DOT 5 brake fluid...it won't eat paint.

[Guest bastaad525]

why cant' they design ALL brake fluids not to eat paint... I've had some bad luck with that lately little splatters getting here and there... thank god it's only a cheap Earl Scheibb paint job or I'd have flipped out. It's alllllmost time for me to strip it back down and just go back to black primer anyways.

 

 

So then I should go with the Dot 4.

[Guest Z Draci]

If you switch to the DOT5 silicone based fluid, you MUST flush out every single drop of your old DOT3 or 4 fluid. They don't mix.

 

DOT5 fluid is a very good type of fluid to use granted you have a very well sealed system. If even a drop of water gets in, you have to flush and do it all over again.

It's good for race cars that have to flush their system after every race.

 

There are DOT4 fluid that has amazingly high boiling points now. Try looking for Motul motorcycle racing fluid.

[TimZ]

It's good for race cars that have to flush their system after every race.

 

Although I agree with everything else in the last post, this statement is not correct. Silicone-based DOT5 is probably the worst choice for race cars, due to its previously mentioned heat expansion characteristics. Basically it causes a soft pedal when the brakes heat up - this is well documented.

 

DOT5 silicone based fluid is only good for show cars that are not driven often, and are not raced.

 

Also note that DOT5.1 is not silicone based, and is a good choice for performance applications.

[awd92gsx]

I'm not 100% sure if this is true on Datsuns or not...but...

 

As a Mits tech I've seen people use Dot 5 in their cars only to have it swell up every seal in the entire braking system. This has caused more than one customer to have to replace every caliper/wheel cylinder/master cylinder/other sealed component in their vehicle.

 

Just stick with Dot 4 and you'll be safe!!

[Afshin]

Here is a very long summary about brake fluid from my files that I had posted a while back:

 

DOT 3,4 and 5.1 fluid are all glycol based and generally compatible. However one may offset the benefit of the better fluid if mixing it with lower grade, so it’s always better to flush the whole system with the newer fluid. Also some are more different than others despite the same DOT rating, ie synthetic, different viscosities and different amount of hygroscopic (water absorbing) properties causing them to absorb brake system moisture, and over time the boiling point is gradually reduced.

 

The Dry Boiling Point is the temperature at which a brake fluid will boil when new in its non-contaminated state and the wet boiling Point is the temperature a brake fluid will boil after it has been fully saturated with moisture. The requirement for wet boiling point minimum is 284F for DOT 3, 311F for DOT 4 and 356F for DOT 5.1. These numbers are the minimum and many of the better brands far exceed the minimum requirement (e.g. castrol SRF has wet boiling of 518F, dry boiling of 590F).

 

Difference between Dot 4 and 5.1:

DOT 5.1, albeit confusing in designation, is effectively a lighter viscosity synthetic poly glycol fluid with DOT 4 performance parameters. It was developed for use in mechanical ABS systems that require a higher cyclic rate to better deal with pulsations. It is not a “higher “performing fluid.

 

DOT 5 is a silicone based synthetic fluid originally designed for use in military and government vehicles where regular maintenance could be problematic. It is non corrosive and is marketed as a “lifetime†fluid often used to preserve brake systems in antique vehicles and those that sit for long periods of time between use. It was never intended for high performance application. DOT 5 fluid is not hygroscopic, so it does not absorb water and may be useful where water absorption is a problem as one of the reason for its development (military equipment and tropical environment..). However and perhaps ironically this brings up another serious concern as moisture enters the system (can not be prevented), it is not absorbed by the fluid, and can result in moisture collecting in the calipers which can very easily boil causing vapor lock and system failure or can cause corrosion where the water collect (it has to collect somewhere since it is not absorbed). DOT 5 fluid is now most used/best suited for show car applications where its anti-corrosion and paint friendly characteristics (does nor ruin paint) are important. DOT 5 is not compatible and can not be mixed with other fluids since it can result in slugging.

I think previously some race teams used to use DOT 5 it because of it’s higher boiling point, however the new poly-glycol synthetic fluid have the same or even better boiling point along with better pedal feel (dot 5 is more compressible and has spongier pedal feel) so DOT 5 has fallen out of favor.

 

Personal recommendations:

DOT 3 is outdated and not suited for aggressively driven cars, dot 5 is problematic and should be avoided. DOT 5.1 is good and best suited for ABS systems which leave us with dot 4.

 

 

-Castrol SRF. amazing fluid, (wet/dry 518/590F) very low hygroscopic affinity (does not absorb much water) and the highest boiling points, and the most expensive by far (actually it is a silicon ester not a glycol based fluid, but it is not the same as the dot 5 plain silicon which can't be contaminated with glycol based fluid)

-Castrol LMA. (LMA=low moisture affinity) cheap, available at most stores, not race fluid but very good as low maintenance and high performing fluid and is actually suitable for most aggressive street applications and can still handle occasional track days with vented rotors.. (wet/dry boiling 325/490)

-Motul 600 one of the best race fluid(based on wet/dry boiling point of 421/585F) along with Neo (identical) but is also very well priced, can be used for daily street/track cars. Does absorb more water (more, but not extremely hygroscopic like most race fluids which need to be changed very very frequently).Great choice if car goes to track often, if you don't leave fluid in over 8-12 months and if live in a dryer climate.

-Ate type 200 also known as super blue and super gold (wet/dry of 392/536F). Outstanding fluid good for race and street, can last for two years (not racing off course). This fluid is possibly the best for aggressive street as well as track use type of car/driver. It is also cheap, best found online, has a wet boiling point of 100F greater than the

Ford HD or AP 550 fluids (AP 5.1 matches the Ate but is much more expensive) and works well on the track for me. Also with the different colors for this fluid (blue and gold), when flushing your system you can tell when the new fluid comes in by the color.

 

One last point, while technically the different non DOT 5 fluids are all compatible, it is not advisable to mix them since people have reported poor performance, spongy pedal feels and so on when doing so. It is best to flush the system when upgrading to a better and new fluid.

[Guest bastaad525]

Afshin - sweet thanks for the very detailed/informative post. I was sold on the Neo up until you mentioned about not leaving it in there for two long... I'm pretty bad about changing out my fluid regularly... then again I do live in a very dry climate and dont' drive many miles so maybe I can get away with the Neo for longer than a year?

 

I was going to go with the Ford Motorcraft but that's not on your list So I'll either go with the Castrol SRF or the ATE super blue/gold.

 

I want to clarify one thing... you said the SRF IS silicone, but it WONT get ruined if it mixes with regular fluid? I will be flushing the system anyways but I'm just wondering if I have to worry if even a little bit of the regular fluid stays in there. Also, since the SRF is silicone, does that mean it's 'bad' as far as it's ability to absorb the moisture in the same way that silicone DOT 5 is, meaning I'll have moisture build up in the calipers and corrosion and all that?

 

I'll check around online I think and just pick up some of that ATE.

[Afshin]

The SRF is a silicone ester based fluid, which is different than the regular silicone fluid. It is much better and will not result in problem when mixed with regular glycol based fluid. I would however not mix the two fluids together such as topping the SRF on regular dot 4 (a regular flush should do). I think that the SRF while being arguably the best fluid, may not be worth the extra cost (your pads may fail from the heat before the ATE fluid does...). I would spend the extra money on better pads and upkeep of the brake system. Also, regular flushing of the brake system will do more for you than getting SRF fluid. Lastly, I don't think that the SRF should cause problems with non-absorbed water build up and corrosion.

[cygnusx1]

Baast, I now run ATE Super Blue/Gold. I think it has one of the best bangs for the buck of all the performance fluids. It will damage paint though. Pedal feel is great. I have not had the opportunity to reach the performance limit of this fluid and I probably never will. I switched to this fluid after boiling the stock brakes on cheap no frills fluid. Since then, I have all new brakes but I did use this flud on the stock brakes and it was great.

 

SRF = $$$

[DaEvil]

All I know is that in 2005 Harley Davidson switched to dot 4 because they offer anti skid brakes now and dot 4 handles the heat better

[Guest bastaad525]

Yeah I'm definately gonna switch over to the ATE blue/gold, sounds like great stuff and a good price. I just wish stuff like this was more commonly available... I absolutely detest ordering things and having them shipped since actually recieving them ALWAYS proves to be a pain in the butt.