What’s the Difference Between DOT 3 and DOT 4 Brake Fluid?

John Baker|Feb 27, 2018 10:12 AM

The primary difference between Dot 3 and Dot 4 is their respective boiling points.

I suspect I know your next question.

But first, some background. The U.S. Department of Transportation classifies brake fluid into four main categories:

DOT 3
DOT 4
DOT 5
DOT 5.1

Their primary differences are their wet & dry boiling points and their composition.

DOT 3 is the most common type used in cars and trucks today. DOT 4, however, is gaining popularity due to widespread use of anti-lock braking systems and traction control, which benefit from DOT 4 fluid’s lower viscosity.

DOT 4 is compatible with DOT 3, but features a higher boiling point. DOT 5 is silicone, meaning it doesn’t absorb water. It’s not compatible with the other brake fluids and is used mostly in classic cars that remain in storage for long periods and need a brake fluid that doesn’t absorb water. DOT 5.1, meanwhile, is used in high-performance and heavy-duty applications due to its high boiling point.

Bring it to a boiling point

So now we’re back to boiling point. What does it mean? After all, we’re not cooking this stuff.

Well, in the right operating and ambient conditions, you are cooking it.

Aggressive braking can lead to intense heat.

Braking generates intense heat between the brake pads and rotors. Maybe you’ve seen a race on TV where the producers stick a GoPro under the car to show the brakes literally glowing red when the driver depresses the pedal. The intense heat can vaporize the brake fluid, causing it to become compressible, which leads to a spongy feeling when you apply the brakes.

Braking also places the fluid under intense pressure, potentially causing the fluid to boil. That leaves gas in the lines, which is compressible, leading to a soft pedal. In racing and performance-driving circles, this is known as brake fade, and it’s something drivers actively want to avoid. To drive as effectively and safely as possible, the driver must be confident that the brakes will perform on lap 10 as they did on lap one.

Brake fade can also come from the brake pad/rotor interface. The pads release gasses as well, which reduces contact between the pads and rotors. That’s why high-end rotors are slotted and drilled – to release gasses quicker, limiting fade.

Brake fade isn’t just for racers

Brake fade can affect nearly anyone. Descending a steep hill, especially when hauling a heavy load or towing a trailer, can generate tremendous heat if you ride or pump the brakes.

PRO TIP: Next time, downshift into a lower gear before descending a steep incline.

By the time you reach the bottom, your pedal may go nearly to the floor, making your heart rate go nearly through the roof.

If you like to toss your vehicle around a curvy country road for a little therapy, standing on the brakes going into corners can create sufficient heat to cause brake fade, too. If you get a little too zealous, you may end up going right through a corner and into the woods.

The fluid’s boiling point indicates the temperature at which the brake fluid vaporizes. The higher the DOT classification, the higher the boiling point, thus the better the fluid is at resisting heat. That’s why racers use DOT 4, not DOT 3, brake fluid.

Boiling point is separated into dry & wet boiling points

The dry boiling point is determined using fresh fluid straight from a new container. The fluid’s wet boiling point is determined using fluid that’s been contaminated with 3.7 percent water, thus it’s always lower than the dry boiling point. Why would test administrators contaminate good fluid? Because it’s a reflection of what happens in the real world.

Brake fluid is hygroscopic, meaning it absorbs water (except silicone-based DOT 5 brake fluid). DOT 3 fluid, for example, can absorb up to two percent water every year. Moisture can enter the system when you remove the reservoir cap to add fluid, through worn seals and even through the rubber brake lines themselves. Thus the fluid’s wet boiling point is the number that more accurately represents what’s really going on in your vehicle.

Which makes it important to periodically flush the brake system and replace the fluid to remove moisture. Otherwise, not only will your brakes become spongy and unsafe, the moisture will slowly corrode metal components.

A good rule of thumb is to change the brake fluid every other year in passenger vehicles, and at least every year in racing vehicles. The AAA says 88 percent of motorists overlook brake maintenance, so you’re not alone if you haven’t changed brake fluid in awhile, like since you bought your vehicle.

It’s not too late to start, though. And when you do, check out our line of brake fluids for your vehicle. The easiest way to determine the correct brake fluid for you vehicle is to use our Product Guide.

Find AMSOIL Brake Fluid for my Vehicle

Sioux Falls Webmaster note: AMSOIL’s Dot 4 outperforms it’s new 5.1 because the 4 is designed purely as a racing brake fluid where as the 5.1 id the latest for all uses yet still beyond the minimum standard.

What’s the Best Hearing Protection for the Gun Range?

Mark Nyholm|Jun 28, 2018 11:28 AM

Summer weather is finally here, at least for us in the northern half of the U.S. and Canada. The longest day of the year, June 21 – the summer solstice – has come and gone. As someone pointed out to me, we’re on the backside of long days here in Sioux Falls and they are only getting shorter. “Kind of depressing,” I said.

This can only mean one thing: we are losing precious minutes at the range to sharpen our skills. Whether you are a single-projective guy/gal sharpening your skills beyond 300 yards or you’re deep into the trap or sporting clays season, get out there and take advantage of the long days.

What? Hearing protection?

One topic of scrutiny and personal opinion is hearing protection. If you don’t wear shooting hearing protection, shame on you. Ask anyone in his or her elder years about hearing. You may have to speak up or repeat yourself, like I have to with my father. He or she will tell you long-term abuse of your ears is no fun in your golden years.

Unfortunately, everyone you talk to about the “best” hearing protection will give you a personal “best” answer. That’s why there are so many options for hearing protection. Wade with me into the deep end of the pond and we’ll cut through the “insider-baseball” information and try to simplify.

It’s all about decibel reduction

The end game with shooting hearing protection is decibel reduction. The greater the decibel reduction, the better.

What’s the threshold for protection? According to OSHA, a conversation is about 60dB and the threshold for pain is about 140dB. Anyone exposed to 85dB for more than eight hours must wear hearing protection. Exposure to about 110dB for just one minute can cause permanent damage.

What is the decibel level of a firearm?

Probably 95 percent of firearms produce more than 140dB
Even a simple .22-caliber rifle is about 140dB
Big-bore firearms and shotguns can produce more than 175dB

What was the threshold of pain again? You got it – shooting a firearm without ear protection puts you in harm’s way.

Now that we know what our ears can take, what is the best way to help protect them?

When shopping for hearing protection, look for its Noise Reduction Rating (NRR).

Every product marketed to help protect your ears and reduce noise has this rating. The higher the number, the better. If the product doesn’t list the NRR, stay away from it. Most of the cheaper foam ear plugs offer decibel reduction in the low 20s to low 30s. That’s not bad for the cost.

But be careful – the NRR assumes the plug is seated completely in your ear. Ineffective seating is the largest issue with these plugs, and most people don’t use them properly.

Simple foam ear plugs are fine for inexpensively protecting your hearing (if used correctly). Quite frankly, though, I don’t understand spending $3,000 on a firearm and only $1 on a 10-pack of ear plugs. What costs more, good ear protection or the hearing aids you will be buying in your elder years?

Custom-fit ear plugs are better

If you are looking for the Cadillac of foam-insert ear protection, look for custom-fit ear plugs. They come with instructions to insert the provided material into your ear and wait. The material dries and forms to your ear. They provide their claimed NRR since they fit properly into your ear. Instead of about $0.25 a pair, they cost around $15 a pair. But that’s still cheap for what they do.

Noise-canceling ear muffs

Looking for the best hearing protection available? Noise-canceling ear muffs are about the best you can get. They come in a range of qualities and prices, from about $20 to more than $100.

They electronically measure and dull sound in fractions of a second. Many allow you to hear a normal conversation while wearing them. When the bang goes off, however, they immediately compensate to protect your ears. You’ll find many brands out there with lots of options. Like to listen to music while shooting? Many options have you covered.

Beware the bulk, though

Although noise-canceling ear muffs are likely the best and most convenient, they are also the most bulky. Many people don’t like all that bulk at the side of their head as they shoot at the range or on the sporting clays course.

I could continue go on. The reason this topic is so complicated is because every ear is shaped differently and everyone has his or her preference.

In the end, find something that combines comfortable with the highest NRR rating you can find. A brand I like has the slogan, “Protect it, or lose it.” I couldn’t have said it better.

As always, happy shooting…and be careful, especially with those ears.

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