Brake fluid DOT3 vs DOT4

[Fabmanrich]

Did a brake job on my daughter's 87 Volvo last week-end. After finishing, as i was logging the work done and mileage in the book I noticed it called for DOT4 fluid. I used DOT3 fluid, I bleed all 4 calipers quite a bit to flush and remove all air bubbles. What is the difference between the fluids? Should I replace with DOT4? What would happen if I leave the DOT3 in?
Thanks,

Richie

 

[Ken2]

The Volvo actually requires DOT4+ (same as DOT5.1). The difference is two things...the higher wet boiling temperature and the difference in the chemical composition to give it that high boiling point.

One excellent brand of DOT4+ brake fluid is ATE. Their blue-dyed fluid makes it easy to see when all the oil fluid is gone. The next time, ATE amber can be used.


Ken

 

[1maniac]

Ditto on the ATE fluid. It's all I run in my BMW which also requires DOT4

 

[Silk]

I have heard,but can't find the source now - that DOT3 has a higher boiling point than DOT4,but DOT3 is more hydroscopic,so needs changing more.

 

[Ken4]

I stick to DOT3 for my Toyotas. Here are some good articles on brake fluid:

http://www.popularmechanics.com/automotive/sub_care_clinic/1302781.html?page=2&c=y

http://hostingprod.com/@aa1car.com/library/bfluid.htm

http://www.babcox.com/editorial/bf/bf110212.htm

http://www.stoptech.com/whitepapers/brakefluid1a.htm

 

[terminaldegree]

quote:

---

Originally posted by Silk:
I have heard,but can't find the source now - that DOT3 has a higher boiling point than DOT4,but DOT3 is more hydroscopic,so needs changing more.

---

I think you may have it backwards.
I just did a brake job on my car the other day and was reading about this.
Dot 4 has higher boiling points [good] than dot 3
but Dot 4 will break down faster than dot 3 in terms of maintaining those boiling points, I think due to its being more hydroscopic.

I'm no expert at this, but with regard to the original question, if it's not a lot of hassle, I would bleed out the Dot 3 in your Volvo and get the factory spec back in there. The braking performance of my Mom's '88 740 was always quite amazing, when we weren't replacing brake parts or a/c compressors...

 

[VaderSS]

quote:

---

Originally posted by terminaldegree:

Dot 4 has higher boiling points [good] than dot 3
but Dot 4 will break down faster than dot 3 in terms of maintaining those boiling points, I think due to its being more hydroscopic.

---

It is a fact that DOT4 has a higher minimum boiling point. That does not mean that all DOT3 fluids have a lower boiling point than all DOT4 fluids. Ford's DOT3 fluid had a 550F dry boiling point and the DOT4 minimum is 446. However the Ford fluid's Wet boiling point keep it a 3. Ford's fluid is one of the most hygroscopic of all though.

I also have yet to see a credible source that says DOT 4 is more hygroscopic by nature, or that it breaks down any sooner. I feel that the DOT3 vs DOT4 arguments are full of myth and urban legend. I feel there is more difference between individual fluids, than the general types, in this regard.

This is an old list, not sure how accurate it is;


ARRANGED BY DRY BOILING POINT:

DRY:401F -- WET:284F --- DOT3 MINIMUM
DRY:446F -- WET:311F --- DOT4 MINIMUM
DRY:446F -- WET:311F --- Castrol LMA DOT 3/4
DRY:500F -- WET:356F --- DOT5 MINIMUM
DRY:502F -- WET:343F --- VALVOLINE SYNPOWER
DRY:509F -- WET:365F --- MOTUL 5.1
DRY:527F -- WET:302F --- AP RACING 551
DRY:536F -- WET:392F --- ATE SUPERBLUE/TYP200
DRY:550F -- WET:290F --- Ford Heavy Duty DOT 3
DRY:590F -- WET:410F --- AP RACING 600
DRY:590F -- WET:518F --- CASTROL SRF
DRY:593F -- WET:420F --- MOTUL RBF600
DRY:610F -- WET:421F --- NEO-SYNTHETIC SUPER DOT 610
DRY:620F -- WET:425F --- COBALT SUPER XRF

ARRANGED BY WET BOILING POINT:

DRY:401F -- WET:284F --- DOT3 MINIMUM
DRY:550F -- WET:290F --- Ford Heavy Duty DOT 3
DRY:527F -- WET:302F --- AP RACING 551
DRY:446F -- WET:311F --- DOT4 MINIMUM
DRY:446F -- WET:311F --- Castrol LMA DOT 3/4
DRY:502F -- WET:343F --- VALVOLINE SYNPOWER
DRY:500F -- WET:356F --- DOT5 MINIMUM
DRY:509F -- WET:365F --- MOTUL 5.1
DRY:536F -- WET:392F --- ATE SUPERBLUE/TYP200
DRY:590F -- WET:410F --- AP RACING 600
DRY:593F -- WET:420F --- MOTUL RBF600
DRY:610F -- WET:421F --- NEO-SYNTHETIC SUPER DOT 610
DRY:620F -- WET:425F --- COBALT SUPER XRF
DRY:590F -- WET:518F --- CASTROL SRF

DOT5 is a silicon based fluid and not at all compatable with DOT3/4/5.1

 

[labman]

Have you ever experienced brake fluid boiling in a street machine, or know somebody that has? Unless you are using metallic or ceramic pads, your brakes are going to fade long before the fluid boils. If the fluid did boil, the increased volume would push fluid back to the master cylinder and over flow it. You would have no pedal, and a strong, sweet smell of the glycol ethers. A firm pedal and a burned smell of phenolic or epoxy, means the lining overheated.

I started using Prestone disk Brake fluid in the late 60's in my TR-4. I think it evolved into DOT-4. I have used nothing else since and never have had any problems with it.

Don't worry about the DOT-3.

 

[Fabmanrich]

Thanks guys, you gave some food for thought (haven't checked those links yet, Ken). The stuff that was in it when we got it was clear, not blue or amber. The different color sure would make it easier when flushing.

Richie

 

[Big Jim]

I certainly would not be overconcerned with using DOT 3 in that application for street use. I would probably change it sooner than I might otherwise do, and I would use Castrol LMA or Valvoline Synpower. It certainly is not an emergency situation unless the car is typically driven very hard.