DOT 4 Brake Fluid – Dave’s Garage

DOT 4 fluid, which has a higher minimum boiling temperature requirement (446 degrees F dry and 311 degrees wet) soaks up moisture at a slower rate but suffers an even sharper drop in boiling temperature as moisture accumulates. Three percent water will lower the boiling point as much as 50%! Considering the fact that today’s front-wheel drive brake systems with semi-metallic linings run significantly hotter than their rear-wheel drive counterparts, high brake temperatures require fluid that can take the heat. But as we said earlier, the brake fluid in many of today’s vehicles cannot because it is old and full of moisture. Water contamination increases the danger of brake failure because vapor pockets can form if the fluid gets too hot. Vapor displaces fluid and is compressible, so when the brakes are applied the pedal may go all the way to the floor without applying the brakes! In addition to the safety issue, water-laden brake fluid promotes corrosion and pitting in caliper pistons and bores, wheel cylinders, master cylinders, steel brake lines and ABS modulators. FLUID RELATED BRAKE FAILURES From time to time we hear about reports of “unexplained” brake failures that caused accidents. When the vehicle’s brakes are inspected, no apparent mechanical fault can be found. The fluid level is normal, the linings are within specifications, the hydraulics appear to be working normally and the pedal feels firm. Yet the brakes failed. Why? Because something made the brakes hot, which in turn overheated the fluid causing it to boil. The underlying cause often turns out to be a dragging rear parking brake that does not release. But that’s another story. The same kind of sudden brake failure due to fluid boil may occur in any driving situation that puts undue stress on the brakes: a sudden panic stop followed by another, mountain driving, towing a trailer, hard driving, etc. A case in point: A child was killed in an accident when the five-year old minivan with 79,000 miles on it his parents were driving suffered loss of pedal and crashed while the family was driving in the mountains of Washington state. Fluid boil was blamed as the cause of the accident.

OEM Brake Fluid Recommendations

  • Acura: 36 months
  • Audi: 24 months
  • BMW: 24 months, or when indicated by Service Inspection Indicator
  • Honda: 36 months
  • Jaguar: 24 months all models except 2009 XF (36 months)
  • Land Rover: 36 months
  • Lexus: 36 months or 30,000 miles, which ever comes first
  • Mercedes-Benz: 24 months
  • MINI 24 months
  • Saab: 48 months (all models except 9-7X)
  • Smart: 24 months or 20,000 miles, which ever comes first
  • Subaru: 30 months or 30,000 miles (normal service) or 15 months/15,000 miles (severe service)
  • Suzuki: 24 months or 30,000 miles, which ever comes first (Forenza & Reno), 60 months or 60,000 miles (Grand Vitara and SX4)
  • Volkswagen: 24 months (New Beetle, City Gold, City Jetta), 36 months (all other models except Routan)
  • Volvo: 24 months or 37,000 miles (Normal), or 12 months (severe service)

Source for fluid change recommendations: Vehicle Manufacturer service information & owners manuals If motorists would only follow this simple advice to change their brake fluid periodically, they could greatly reduce the risks associated with moisture-contaminated brake fluid. You can extend the life of your brake system and likely save yourself a lot of money in the long run on brake repairs, especially if your vehicle is equipped with ABS (because ABS modulators are very expensive to replace!).

Testing Brake Fluid

Since you can’t tell how badly contaminated brake fluid is by its appearance alone (unless the fluid is full of rust or is muddy brown), the fluid should be tested unless you are changing it for preventive maintenance or as part of a brake job. There are three ways to check the condition of the brake fluid: Chemical test strips. A chemical test strip made by Phoenix Systems (888-749-7977) called “Strip Dip” can reveal the condition of the corrosion inhibitors in the brake fluid. The FASCAR chemicals react to the presence of copper in the fluid. The test strip changes color to reveal the condition of the fluid. When copper levels reach 100, it indicates the corrosion inhibitors are nearing the end of their life. If the copper level is 200 or higher, the corrosion inhibitors are worn out and the fluid needs to be changed.

Electronic brake fluid testers actually measure the fluid’s boiling point. The test takes only about a minute and is quite accurate. If the fluid’s boiling temperature is getting dangerously low, replacement is recommended to minimize the risks of pedal fade caused by fluid boil. Sources for electronic brake fluid testers include Alba Diagnostics, MISCO and OTC.

Changing Brake Fluid

When the fluid is changed, use the type of brake fluid (DOT 3 or 4) specified by the vehicle manufacturer. The cap on the fluid reservoir will usually indicate what type of brake fluid is required. You can also find this information in your Owners Manual (look under brake fluid). As any brake fluid supplier will tell you, brake fluid is NOT a generic product. Just because a fluid meets the minimum DOT 3 or DOT 4 specifications does not mean it can tolerate moisture or provide the same degree of corrosion protection as another brand of fluid. Raybestos, for example, sells a “Super Stop Super High Performance” DOT 3 fluid with a dry boiling point of 550 degree F, which meets Ford’s latest requirements. There are also high temperature glycol based DOT 5.1 brake fluids (not to be confused with DOT 5 which is silicone based). The dry boiling temperature rating for DOT 5.1 is 518º F or higher, and the wet boiling temperature rating is 375º F or higher. Some racing brake fluids exceed the dry boiling temperature rating, but may only meet the wet boiling temperature requirements for DOT 3 fluid (284 degrees). So the next time you are inspecting or servicing your brakes, be sure to check the condition of the fluid as well as the level. If you add or change fluid, use type specified by the vehicle manufacturer (DOT 3 or 4) and use the highest quality fluid you can get. And above all, remember the benefits of changing the brake fluid for preventive maintenance.

Please email all inquiries to: Dave
or snail mail
32 Turkey Hill Road
Richmond VT 05477

Brake Fluid 101

I was driving dad’s car hauler through Smuggler’s Notch last fall bringing a car back from Stowe when I got a sobering lesson on why it is important to replace brake fluid. As I was passing the waterfalls in the Notch, the sedan with out of state plates in front of me abruptly stopped in the middle of the road to take a picture of the waterfall. I stomped on the brakes and came to an abrupt stop. Annoying, but no big deal. Moments later as I was descending the Jeffersonville side of the notch I tapped the brake as the truck started to run away at the top of the hill. No brakes. I pressed harder and harder on the pedal, but the truck was still speeding up. I manually down shifted and continued to thump on the brake. White smoke was now pouring off both front wheels. Ever notice that there is no runaway truck ramp there? I was able to stop the truck eventually. I pulled off to the side of the road and allowed the brakes to cool. How did this happen? The truck had just had the front pads replaced. When I looked at the brake fluid instead of a clear-yellow color, it looked more like grape juice. My theory is this: The new pads were slightly wider, creating some drag and some heat. The pistons were recently pushed back in to the calipers to accept the new pads, dirty contaminated fluid probably caused some rust on the caliper bores, causing the pistons to stick a little. The heat caused the brake fluid to boil, reducing the ability of it to compress the pads against the rotors. I changed the fluid, and exercised the pistons in and out a few times. Something the shop that replaced the pads should have done.

I have been using DOT 5, or silicone fluid in the antique cars for years with good results. Silicone fluid does not absorb moisture, so is perfect for antique cars. In the last year I have done the brakes on two MG cars that had conventional fluid, and one that I had changed over to Silicone fluid in 1988. The two with the conventional fluid had considerable corrosion in both the wheel cylinders and in the master cylinder. One MG, the green 1949 TC had half of the wheel cylinder pistons actually frozen. This car has marginal brakes to begin with, with half the wheel cylinder pistons frozen it was simply unsafe. The other MG had functional brakes when it was in a bad accident in 1999. The fluid was obviously in need of replacement, because all of the pistons became seized in their bores, requiring a great deal of effort to remove. The MG with the Silicone fluid had no corrosion in the master cylinder or the wheel cylinders. This is the black 1955 that is undergoing a total restoration, so I went through the brake system replacing all the metal brake lines, rubber hoses and seals. I have heard the horror stories of how the silicone fluid dissolved rubber parts, but have never seen any evidence of that or read anything that suggests this is really possible. My guess is that these owners would have experienced this regardless of what type of brake fluid was in their car. If you use DOT 3 or DOT 4 in your antique car I suggest you replace the fluid every two years, or switch to Silicone fluid. One other benefit to Silicone fluid is that it will not harm your paint. This is a great bonus for those master cylinders that are hard to fill without spillage. Just remember the old Midas commercial slogan, “the most important part of your car isn’t what makes it go, it is what makes it STOP!”

Why Change Brake Fluid?

Copyright AA1Car Brake Fluid is a hot topic because most people don’t know why it should be changed. Did you know the average motorist who drives 10,000 to 15,000 miles a year uses his brakes about 75,000 times a year? Did you know that nearly half of all motorists in a recent Car Care Council survey said brake failure was their number one fear amongst driving emergencies? So consider this: After three years of service, the average boiling point of the brake fluid has dropped to a potentially dangerous level because of moisture contamination and may not meet minimum federal requirements for brake fluid. Probably half of all cars and light trucks that are 10 or more years old in the U.S. have never had their brake fluid changed. Yet in many European countries, regular brake fluid checks are required, and half of all cars routinely fail such tests. That’s a good case for changing brake fluid. REPLACE BRAKE FLUID Brake fluid is one of the most neglected fluid in vehicles today, yet is vitally important for safe driving. Consequently, professional technicians should be checking the fluid and recommending that the brake fluid be changed if it is contaminated. The issue is old brake fluid may not be safe if moisture contamination is above a certain level.

Brake Fluid Preventative Maintenance

Many experts have long recommend changing the brake fluid every year or two for preventative maintenance. Their rationale is based on the fact that glycol-based brake fluid starts to absorb moisture from the moment it is put in the system. The fluid attracts moisture through microscopic pores in rubber hoses, past seals and exposure to the air. The problem is obviously worse in wet climates where humidity is high. After only a year of service, the brake fluid in the average vehicle may contain as much as two percent water. After 18 months, the level of contamination can be as high as three percent. And after several years of service, it is not unusual to find brake fluid that contains as much as seven to eight percent water.

An NHTSA survey found that the brake fluid in 20% of 1,720 vehicles sampled contained 5% or more water! As the concentration of moisture increases, it causes a sharp drop in the fluid’s boiling temperature. Brand new DOT 3 brake fluid must have a dry (no moisture) boiling point of at least 401 degrees F, and a wet (moisture-saturated) boiling point of no less than 284 degrees. Most new DOT 3 fluids exceed these requirements and have a dry boiling point that ranges from 460 degrees up to over 500 degrees. Only one percent water in the fluid can lower the boiling point of a typical DOT 3 fluid to 369 degrees. Two percent water can push the boiling point down to around 320 degrees, and three percent will take it all the way down to 293 degrees, which is getting dangerously close to the mini-mum DOT and OEM requirements.

Dave’s Brake Fluid article will continue in the April Issue

Please email all inquiries to: Dave
or snail mail
32 Turkey Hill Road
Richmond VT 05477

ZDDP engine oil

Are you aware of the non ZDDP engine oil currently on the market, and the potential consequences for the older car market? The EPA has forced the reduction or elimination of ZDDP (Zinc Dialkyl-Dithio-Phosphate) from engine oil. ZDDP is curtail for the proper lubrication of flat tappet camshaft engines. Not a problem on modern engines with roller type cam and tappets, but older engines with flat tappets need this layer of protection due to the high pressure and “scuffing” on the tappet. The reduction of these chemicals in supplied oil was based on the fact that zinc, manganese and/or phosphates reduce the effectiveness and eventually damage catalytic converters and introduce minute amounts of pollutants into our atmosphere. In the past there have been horror stories that have scared old car enthusiasts into believing our beloved cars were being destroyed before our very eyes. Remember when we were told that unleaded gas would destroy our valves? It didn’t. It is an undeniable fact that todays engine oil is vastly superior to oils from even several decades ago, and modern type oil has successfully protected engines for hundreds of thousands of trouble free miles. However, the newest engine oils do not have the ZDDP needed for proper tappet and camshaft protection. While they work very well in modern engines, there is a problem with the older, flat tappet engines. In my opinion, there is just too much undeniable science and hard evidence to tell me that this one is one we need to be concerned about. This problem can be easily and inexpensively solved. If nothing else, you can make a choice to buy inexpensive piece of mind with your selection before you pour it in to your crankcase. What can we do? Diesel engine oil still has the ZDDP additives, as do several other oils, including Castrol HD off road, Redline (synthetic) or Valvoline VR1. I have been using Shell Rotella for years with no complaints. We use to use Castrol 20/50 in the MG and Triumph engines, but now use Rotella. It seems to be the oil of choice for the Dodge Cummins Turbo Diesel crowd. These are the people who hop their trucks with larger turbo chargers and performance chips, then use their trucks to haul heavy trailers across the country and back. They are man-aging to easily put over a million trouble free miles on these engines. That is enough proof for me that this oil has proven its worth. Still want to use your favorite oil? Use General Motors (Chevrolet): EOS, their oil fortifier. Add it to your oil, it’s only about $12.00 for each oil change for an 8 ounce can. GM has been aware of this problem for years, and is pushing this product for their older, flat tappet engines. Read the label of the oil you are using, and make sure it states that it still contains the ZDDP additives our older flat tappet engines need. Want further information? There is plenty of it on the web. If you are concerned about this issue (as I feel you should be) then it would be worth your while to do some investigating on the internet. During the February meeting at Vermont Engines we should ask the boys there for their thoughts and observations on this subject.

I received this tip from Rick Reinstein. It is called the “Redi-Rad:” This device allows you to play an mp-3 or Ipod player through an AM radio!! How neat is that? Now we can listen to our tunes as we drive our antique cars with virtually no modification. The unit plugs in between the antenna plug and jack on the radio. It is available from BCE Redi-Rad Store, PO Box 180095, Delafield, WI 53018 USA Telephone #(262)-646-3363

Rick also asked this question:

Hi Dave, “Do you know if anyone sells a gas tank drain petcock? That would make annual draining of our crappy ethanol gas much easier prior to storage”

In “the old days” we used to fill our tank with gasoline and add a fuel stabilizer for winter storage. In the spring we would dump a can of dry gas in the tank (creating ethanol) to remove any moisture, turn the key and be on our way. Now that we have modern ethanol, draining the gas tank is another option. I know there are petcocks for motorcycle gas tanks and on diesel filters. I found no specific application for such a part for an automobile gas tank, but that does not mean there is no such product available. I will continue to look and post any findings here. Siphoning is also an option. If you do drain the tank, I would leave the gas cap off for the winter and place a sock or something over the inlet of the tank to allow moisture to vent, but also prevent anything else from going in the tank. Remember, Ethanol will dissolve older rubber hoses and components. It is possible that the ethanol can destroy part of your fuel system, and the gas can spill out due to gravity. It happened to me last year with my snow blower. The fuel line was weeping gas on to the floor. I discovered it when I smelled gas in the house and found a puddle of gas on the garage floor. When I fixed it, I found a black tarry like goop in the carburetor. If you store your car with a full tank, there is potential for a lot of gasoline to spill out. That could potentially ruin your day (or vehicle, garage, house, etc.) Something else to watch for. Keep those questions coming, send them to and I will do my best to track down the correct answers to your questions.

Please email all inquiries to: Dave
or snail mail
32 Turkey Hill Road
Richmond VT 05477