Dot 3 Or Dot 5 For dodge pickup?

fuzz4fuzz4 Member Posts: 3
edited March 2014 in Dodge
I have been told that I should change my brake fuild. I will be pulling a 32' trailer into the mountaions and was told to change from from Dot 3 to Dot 5 because it would not boil.My truck is a 99 Dodge 2500 longbox with a auto trans. Is this something that is worth while. Thanks


  • dustykdustyk Member Posts: 2,926
    First, it is NOT true that DOT 5 brake fluid will not boil. The difference is the boiling point is higher than DOT 3 or 4.

    You may use DOT 3 or 4 brake fluids in your Dodge truck. You can use DOT 5 fluids, but be aware they ARE NOT compatible with any of the previous DOT versions (DOT 1-4). DOT 3 & 4 are glygol-based fluids and DOT 5 is silicon based.

    (DOT 1 & 2 are drum brake only and obsolete)

    The following is the MINIMUM wet and dry boiling points for DOT-rated brake fluids:

    DOT 2 - 374F dry; 220F wet
    DOT 3 - 401F dry; 284F wet
    DOT 4 - 446F dry; 311F wet
    DOT 5 - 500F wet; 356F wet

    Since DOT 5 is silicone brake fluid and it IS NOT compatible with DOT 3 & 4, it cannot be mixed with the factory-equiped fluid. It must be purged. People who have done this say it is very difficult to completely or effectively purge the old gylgol-based DOT 3 or 4 out of a system. It usually requires several complete purges before all of the DOT 3 or 4 as been 100% evacuated. This can be expensive!

    Besides being very expensive itself, please be aware that DOT 5 is not easy to work with. It is difficult to pour without introducing bubbles and can result in soft pedal or pulling problems because of this. Bubbles do not float up as readily, either. In addition, DOT 5 does not purge moisture from a system as well and any moisture in DOT 5 will gravitate to the lowest point in the system, which is usually the calipers and wheel cylinders, and cause accelerated rusting problems.

    I would not recommend the use of DOT 5. DOT 5 is not as convienently stocked by auto parts stores. If you ever need brake work done, your repair folks would need to know that you had DOT 5 installed since they would not expect to see it in a light-duty pick-up application. If you are concerned about brake fluid temperature, I would strongly consider DOT 4. Personally, I think DOT 3-rated brake fluid is more than enough for your application, but there are a number of high quality DOT 4 aftermarket fluids available.

    Castrol SRF DOT 4 is rated at 590F dry & 518F wet, ATE has a DOT 4 rated at 536F dry & 392F wet and both are reasonably priced.

    Best regards,
  • mledtjemledtje Member Posts: 1,123
    As mentioned by Dusty.

    DOT 5 can and will cause severe problems with anti-lock brakes. Since it is more viscous, the rapid cycling of the solenoids during anti-lock operation will cause air bubbles in the system.

    On the other hand, DOT will not cause rusting of cylinders - rather it will prevent it. I started using DOT several years ago after reading about the results at Harrah's Auto Collection. Even in the dry Nevada desert, they rebuilt brake systems on musuem cars every 3-5 years because of rust. Since they changed to DOT 5 they have not rebuilt another brake system because of rust. DOT 3/4 fluid PULLS moisture out of the air and into the brake fluid. That fluid caused rust - even in dry climates. DOT 5 does pull moisture into the fluid. And if it did, the silicon fluid seals and protects the metal surfaces.

    The 25 year old master cylinder in my motorcycle is notorious for rust and pitting - you can't find a good used one, and new ones are $300. Took mine apart for a rebuild, and the bore is perfect - no rust, no pits, nothing. It has had DOT 5 for 25 years - never been changed either!

    Mike L
  • dustykdustyk Member Posts: 2,926
    >>In addition, DOT 5 does not purge moisture from a system as well and any moisture in DOT 5 will gravitate to the lowest point in the system, which is usually the calipers and wheel cylinders, and cause accelerated rusting problems.<<


    Perhaps I should have worded the above a little differently, but I wasn't claiming that DOT 5 caused rusting because of it's chemical make up.

    You are correct, DOT 4 and below versions will pull moisture from the air. That is why you should avoid removing the master cylinder cover as much as possible. DOT 5 does not have this negative feature and is much more resistant to acquiring moisture.

    The problem is that DOT 5 is much harder to purge existing systems, especially when converting from a DOT 3 or 4. If a system already has some moisture in it, purging with DOT 5 is more problematic because the increased viscous nature tends to decrease the ability to trap and carry out moisture. I have seen some suggest that the first purge or two should be done with a glygol-based brake fluid to ensure complete (as possible) evacuation of moisture, then purge with DOT 5. The one time I was involved with a conversion turned out to be very unsuccessful.

    Since the person who asked the question was only concerned with boiling the fluid, there are alternatives using glygol-based DOT 3 & 4s that can raise the boiling point to the same level as DOT 5 without the DOT 5 complexities. DOT 5 would be my choice if a system were brand new. A practical alternative is to use a DOT 4 or DOT 5 glygol equivilent and purge the system out every two or three years to evacuate moisture. The alternative, from a materials cost perspective at least, is generally going to be much cheaper.

    Best regards,
  • markbuckmarkbuck Member Posts: 1,021
    Is a low viscosity high performance DOT4 compatible brake fluid specifically for ABS systems. Not Silicone based.

    I am currently running this in all my vehicles/race bikes.

    Motul DOT 5.1

    Spendy, but worth it IMHO

    DOT 5.1 Brake Fluid
    LONG LIFE 100% synthetic fluid for hydraulic actuated-brake and clutch systems.
    Fluidity specially designed for anti-locking brake systems.

      LONG LIFE FORMULA: The high wet boiling point (185°c/365°F), is superior to DOT 4 and DOT 3 fluids.
    SPECIALLY DESIGNED FOR ANTI-LOCKING BRAKE SYSTEM (ABS) :Viscosity: (820 centipoises at -40°c / -40°F) lower than DOT 4 and DOT 3 brake fluids, which allows MOTUL BRAKE FLUID DOT 5.1 an easier fluid circulation in micro-valves of anti-locking systems.

This discussion has been closed.