When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Quick question: DOT 3 or DOT 4 brake fluid? Zip Corvette sent DOT 3 to me with my brake overhaul kit and the service center used DOT 4 because they said it was better. What's everyone think?
Some brake fluid eats paint. Some is more hygroscopic. Some is silicon based. Some are backwards compatible, some aren't; that means full alcohol flushes to change out types.
I use DOT 3 in everything. Factory fill was DOT 3.
Me too....
I don't know why DOT 3 is considered bad by some, yes its hygroscopic but if your system is sealed and in good shape it'll be years before you have to deal with it. Prob 1/2 decade, prob more....than a flush and refill and you're on the road again...
If you're ham-fisted and sling fluids all over the place then yes your paint will get carbuncles and you'll deserve it.
I don't know why DOT 3 is considered bad by some, yes its hygroscopic but if your system is sealed and in good shape it'll be years before you have to deal with it. Prob 1/2 decade, prob more....than a flush and refill and you're on the road again...
If you're ham-fisted and sling fluids all over the place then yes your paint will get carbuncles and you'll deserve it.
Best DOT 3, if I remember correctly, was sold by Ford. Used in a lot of performance applications, and had a very high dry boil point. Unsure of part number right now, but could probably find if someone is really interested. I used to use it in my cars awhile back.
For the price ATE BF1200, DOT 4 TYP 200 brake fluid is some of the best you can buy with a wet boiling point of 388°F and a dry boiling point of 536°F. You may find it locally, Advance Auto, Amazon and Tire Rack carry it. You can also get it here for $13 a liter. Excellent value for the money.
Note: always be sure to seal container when not in use and minimize open container time as much as possible to preserve its boiling points.
Good luck... GUSTO
It's been a while since I did detailed research on this topic, but as best I recall the DOT 4, with it's higher boiling temps, is better for high demand applications (e.g., racing). But it attracts water more readily than DOT 3 and can lose its advantage if not changed out periodically. Back when I was doing track days I flushed and replaced the brake fluid with ATE DOT 4 immediately before every event. DOT 3 is more than capable for routine driving and will not need to be changed as often due to water accumulation. I have no experience with DOT 5 or 5.1.
The ATE fluid used to come in both blue and amber. I would alternate so I always knew when the system was flushed as the new color would come through.
5.1 is the same as 3 and 4, but has a higher boiling point with the same negative effect you mentioned. All three are mineral based, can be synthetic and are compatible. DOT 5 is the oddball silicon that is completely incompatible with the others. Personally, I don’t like it but many swear by it.
If the boiling point of Dot 3 fluid isn't high enough in your old Corvette, you're probably running on a race road course or doing something stupid and illegal on public roads.
All my old stuff and Harley have had Dot 5 for years. No corrosion, no sticky, leaky cylinders. Life is good.
It's been a while since I did detailed research on this topic, but as best I recall the DOT 4, with it's higher boiling temps, is better for high demand applications (e.g., racing). But it attracts water more readily than DOT 3 and can lose its advantage if not changed out periodically. Back when I was doing track days I flushed and replaced the brake fluid with ATE DOT 4 immediately before every event. DOT 3 is more than capable for routine driving and will not need to be changed as often due to water accumulation. I have no experience with DOT 5 or 5.1.
Tom, I don't believe (at least I've never read anywhere), that the DOT 4 or 5.1 gain moisture any quicker than DOT 3, under normal use. The minute that any glycol based fluid (DOT 3, 4, 5.1) is exposed to the normal atmosphere (air) it begins to absorb moisture. Most brake reservoirs are not sealed systems, they are vented, so they can begin to absorb moisture over time. Just bleeding the system periodically (as racers frequently do) will expose the reservoir to the atmosphere and over time the fluid will become 'wet'.
In your case (and that of anyone engaging in road racing) where brakes are critical to your ability to push the car as hard and fast as your brakes (and tires) can control, it only makes sense to replace your fluid before every event with fresh 'dry' fluid, as you did.
One thing and reason I like the ATE BF1200 brake fluid is it's boiling point is high enough (both wet and dry) to be classified as DOT 5.1. Yet is readily available and about the same price as most DOT 3 fluids at your local auto parts store. I keep a couple of unopened liters of it on hand for routine servicing and whenever flushing and replacing fluid as preventive maintenance.
If the boiling point of Dot 3 fluid isn't high enough in your old Corvette, you're probably running on a race road course or doing something stupid and illegal on public roads.
All my old stuff and Harley have had Dot 5 for years. No corrosion, no sticky, leaky cylinders. Life is good.
These cars have station wagon brakes in a lighter vehicle and are mucho overkill. If you're running on the edge of brake failure with the stock setup, then, yes, either racing or testing the laws of natural selection...
Last edited by Frankie the Fink; 06-24-2019 at 12:04 PM.
Tom, I don't believe (at least I've never read anywhere), that the DOT 4 or 5.1 gain moisture any quicker than DOT 3, under normal use. The minute that any glycol based fluid (DOT 3, 4, 5.1) is exposed to the normal atmosphere (air) it begins to absorb moisture. Most brake reservoirs are not sealed systems, they are vented, so they can begin to absorb moisture over time. Just bleeding the system periodically (as racers frequently do) will expose the reservoir to the atmosphere and over time the fluid will become 'wet'.
In your case (and that of anyone engaging in road racing) where brakes are critical to your ability to push the car as hard and fast as your brakes (and tires) can control, it only makes sense to replace your fluid before every event with fresh 'dry' fluid, as you did.
One thing and reason I like the ATE BF1200 brake fluid is it's boiling point is high enough (both wet and dry) to be classified as DOT 5.1. Yet is readily available and about the same price as most DOT 3 fluids at your local auto parts store. I keep a couple of unopened liters of it on hand for routine servicing and whenever flushing and replacing fluid as preventive maintenance.
Good luck... GUSTO
Gusto:
Minor point, but most brake fluid reservoir I know have a rubber diaphragm seal on the top under/built into the cap. They are not directly open to air. Brake fluid expansion and contraction and fluid use due to pad wear just flexes the diaphragm or pulls it down a bit into the fluid reservoir.
Minor point, but most brake fluid reservoir I know have a rubber diaphragm seal on the top under/built into the cap. They are not directly open to air. Brake fluid expansion and contraction and fluid use due to pad wear just flexes the diaphragm or pulls it down a bit into the fluid reservoir.
In your case (and that of anyone engaging in road racing) where brakes are critical to your ability to push the car as hard and fast as your brakes (and tires) can control, it only makes sense to replace your fluid before every event with fresh 'dry' fluid, as you did.
This is very true if your track car uses glycol-based brake fluid.
However, DOT 5 fluid makes this pre-race ritual unnecessary.
My vintage racer (see avatar) and my bride's track car both have DOT 5 fluid in the brake systems. I never, ever had to bleed the brakes before going to the track. And neither car ever boiled the brake fluid.
I just bought DOT 5, due to some of the past threads on here, for my freshly installed brake lines and master cylinder. My 65 will be an occasional driver and that's it. As a matter of a fact, I'm headed to pick up my order when I leave work today and then, hopefully, bleed my brakes.
06-23-2019, 11:44 AM
Brake fluid
Dennis
Best DOT 3, if I remember correctly, was sold by Ford. Used in a lot of performance applications, and had a very high dry boil point. Unsure of part number right now, but could probably find if someone is really interested. I used to use it in my cars awhile back.
