Brake fluid DOT 3 vs. DOT 4?

[asand1]

This weekend I plan to flush my brake fluid. I hsave been driving on the fluid I purchased my car with 3 years ago. I have no idea the age, and just want it done. I know DOT 3 and 4 are compatible and interchangeable, but I do not know the advantages of DOT 4.
Is DOT 4 more desirable? Is it more resistant to heat or water intrusion?

 

[97prizm]

The DOT Spec in brake fluid is designed to tell the consumer the wet and dry boiling points of each spec. Brake Fluid Chart
Be forewarned DOT 5 is not compatible as it is silicone based fluid, 5.1 is glycol fluid.

 

[asand1]

Thank you, I just Googled and discovered DOT 3,4, and 5.1 are compatible, but hold different boiling points. I will pick up some DOT 4, although I really don't need it.

 

[tommygunn]

Yes, get the DOT 4 if you can. The boiling points are higher than DOT 3.

It's only a dollar or two more, and sometimes the same price.

Valvoline DOT 4 is often on sale as well.

 

[Ken2]

DOT 3, 4, 4+, and 5.1 are all a polyglycol ether base, but the higher numbers contain some borate compounds (and maybe others) to get the higher boiling points. In a very few cases the elastomers in the brake system might not do well with the higher-than-spec fluid. (I've wondered whether DOT4 fluid in my Toyota caused the master cylinder leak?)

 

[97prizm]

I personally am fairly sure that DOT 4 caused my '84 RX-7 Racecar to leak as well.

 

[46Harry]

My recommendation is to use what the vehicle manufacturer recommends. If DOT 3 is recommended, that is what I would use. Most American and Japanese cars use DOT 3 fluid. Some of the British cars require DOT 4.

 

[tommygunn]

If there's an O'Reilly's near you, get Wagner SevereDuty DOT 5.1, or Pentosin Super DOT 4

 

[asand1]

I'm limited to Napa, Fred Meyer, Bi Mart, or knechts.

 

[The Critic]

Originally Posted By: asand1
I'm limited to Napa, Fred Meyer, Bi Mart, or knechts.


I've used a lot of the Valvoline DOT3/4 fluid and it seems to work fine. Some say that it gives off a slighter softer pedal, but I have not been able to verify this.

You may want to get some Delco Supreme II brake fluid from the GM dealer. It is fortified with additional anti-corrosion inhibitors and other additives that are not found in any over-the-counter DOT3 fluid. GM even considers it to be lifetime fill.

 

[tommygunn]

Originally Posted By: asand1
I'm limited to Napa, Fred Meyer, Bi Mart, or knechts.


NAPA carries Pentosin brake fluid.
If you don't see it on the shelf, as for part number
AIC DOT4SB
or
AIC DOT4LV

Some Napa locations have Castrol brake fluid, which is also a good option.

Barring that, Napa's own NAPA DOT 4 is on sale.

 

[meep]

Originally Posted By: The Critic
Originally Posted By: asand1
I'm limited to Napa, Fred Meyer, Bi Mart, or knechts.


I've used a lot of the Valvoline DOT3/4 fluid and it seems to work fine. Some say that it gives off a slighter softer pedal, but I have not been able to verify this.


I have also noticed softer pedal feel with dot 4. It was especially noticeable on a friend's mid '90 S10. Less so on other vehicles. The S10 already had a lot of pedal travel. the Dot4 brought it close to the firewall. I bled it a second time thinking maybe I'd mistakenly gotten some air in the lines.... and there was no change. It's barely noticeable with other cars, but I did notice it once I became aware of it.

 

[artificialist]

Yes, I get the same weird feeling with Valvoline DOT4.

However, the brake system does function properly, and the fluid stays clean for a long time, so I feel good using it.

Pentosin DOT4LV is supposed to help ABS systems work better by reducing viscosity. I used it in my Mitsubishi and Mom's 2005 Jeep Grand Cherokee because they both have 4 wheel ABS. I haven't noticed a difference in feel, but neither of us have needed to use ABS.