Looking at Wikipedia's DOT 3 page, it looks like it's been effectively superseded by DOT 4 fluid, but it's still sold and is still recommended on many forums. This question has an answer saying DOT 4 can be used in DOT 3 systems, but DOT 5 can't.

If DOT 4 is better, why is DOT 3 still in use? And the real question, which should I use on my bike that calls for DOT 3 (albiet, from 1983).

3 Answers 3


The main difference of DOT3 and DOT4 is boiling point of the fluid.

The DOT3 standard has a lower minimum boiling point requirement then DOT4.

Not all fluids are made equal and they will all typically list what both their Dry and Wet boiling points are.

You can have one DOT3 fluid that just barely makes it past the standard, then another that can handle another 30-40F above that one.

If your bike calls for DOT3, then any DOT3 should be able to safely handle standard situations. Going with a higher quality DOT3 or a DOT4 will give you more tolerance though.

The Dry and Wet numbers are due to moisture build up in the brake lines. When you've first bled and put in new fluid, that fluid is operating in its "Dry" form. Over time, moisture will get into it which will lower its performance to the "Wet" level.

DOT5 is silicon based and is not interchangeable.

There is a similar question although it didn't ask about DOT5, what is the difference between DOT3 and DOT4 brake fluids?

  • Just to add to the confusion, DOT 5.1 is glycol based and thus can be used in place of DOT 3/4, but DOT 5 isn't and can't. Jul 13, 2011 at 1:52

Not all sure how much of this is true but info I so far know and go by, DOT 4 has a higher boiling point and also has borate esters. DOT 5 is silicone based

This is the dry boiling point minimum as I know of;

DOT 3,   205 C  (401 F)
DOT 4,   230 C  (446 F)
DOT 5,   260 C  (500 F)
DOT 5.1, 270 C  (518 F)

In Australia DOT 3 is supposed to have min 230 C boiling point.

From what I learned DOT 2 was supposed to be drum brakes then the introduction of front disk brakes DOT 3, and introduction of all wheel disks DOT 4, and DOT 5.1 late abs but what also happened is Toyota went back to DOT 3 possibly because of viscosity but haven't researched it yet exactly.

I think so far the army is one of few using DOT 5 but are thinking of going back to DOT 3. This I can't back up yet so don't take my word for it.

Having stated this for example the nulon DOT 3 has a boiling point of 260 C and states to not have adverse effect on physical properties of rubber cups and O rings.

I'm not a scientist and some manufacturers can and do make better fluids but I also found over time one will be good for a while then go slack on product.

Once I did get frustrated when I had to diagnose a fault on a car which had front vibration at 70kmh-80kmh then slightly less at 90-100. I did all usual check wheel alignment, balance tyres,check steering rack, replace two lower ball joints, then overhaul calipers and finally found one cup swelled up in a master cylinder and would block a hole which would maintain pressure on front calipers causing front wheels to fight left each other. The fluid just came due for a flush and was DOT 4 and I'm aware it's also true it can depend on car use and storage for fluid to need earlier flush.

Once I did a concentric clutch conversion on a car from ram clutches and ram clutch recommended only DOT 3 stating other brake fluids can affect the rubber components.

So my conclusion is use the recommended DOT but if necessary can mix DOT 3 and 4 only if last choice but then flush properly with correct fluid with two people not just gravity bleed because this stirs up everything in slaves and calipers and gives better indication when old fluid is flushed.


DOT 3 is strictly mineral based,all DOT 4 is a synthetic blend fluid.DOT 3 still exists largely due to its lower cost,being compatible with many vehicles still on the road.For the cost difference DOT 4 advantages out weigh the small amount of cost difference.The Castrol website posts the advantages to DOT 4

1.)Maintains a higher boiling point than conventional brake fluids. 2.)Superior protection against chloride and zinc corrosion of braking system parts.

Brake fluid that boils in a closed system will vaporize which acts like air in the lines and stopping power will be greatly reduce

  • 1
    I'm not sure this answers the question. Also, DOT 3 and 4 can both be made out of glycol ether, while DOT 4 can be made out of borate ester. Neither of these are mineral based (you saying "mineral based" implies made from mineral oil ... maybe you need to rephrase). DOT 4 can be used in place of DOT 3 fluid. The main difference between the two is the boiling point. If you have references proving exactly what you are saying, please add them in the text to better clarify what you are trying to say. Aug 31, 2015 at 15:31

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .