j curtiss

The subject message is boldly displayed on the brake master cylinder cap of my '99 C5. Notably, DOT 4 brake fluid has a higher boiling point than DOT 3 and, therefore, would appear to be a superior fluid to use? However, the warning suggests that there's a problem with using DOT 4fluid. Does anyone know what the issue is here? The same goes for the clutch fluid. I assume DOT 4 fluid must adversely react with the elastomer seals in the brake and clutch system - hence the warning?

Thanks,

ZeeOSix

I believe DOT 4 is compatable with DOT 3. Look on the back of the bottle and it should say, or it may be labled "DOT 3/DOT 4".

I've used DOT 4 (Valvloline SynTech) in my clutch master cylinder and no ill effects seen.

http://www.valvoline.com/pages/produ...asp?product=51

From the link below:
"DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point."

http://www.xs11.com/tips/maintenance/maint1.shtml

My read is that DOT 3 and DOT 4 are fully compatable. More into to back that up:

http://www.cartalk.com/content/colum...August/02.html

BrianG01

Dot3/4 is fine in these cars for the brake and clutch systems. Dont go anywhere near Dot 5, thats where the trouble is.

If dot 3 is an orange...

Dot 4 = a better juicier orange.

Dot 5 = an apple. An apple that will cost you a hell of a lot of money.

Mr. Lucky

DOT 4 fluid has a higher viscosity, which could be an issue in cold climates.

cruisemon

Never have understood the DOT 3-4 thing because they are essentially the same fluid except DOT 4 has borate esters in it to raise the boiling point to 440F from 401F. DOT 5 silicone is another story and maybe this is why there is the admonition. DOT 5 doesn't absorb water like DOT 3-4 and boils at 500F but unlike any other liquid, it is compressible, which can make for spongy brakes. And if it DOES get water in it and the water migrates to a caliper, since the oil and water are not miscible the water will boil at 212F and now we're really talking compressible, as in NO brakes.

Charlie

Boob

I've hear to use only non-synthetic Dot 3. As a result that's what I've been using. I just try to change the fluid in the res at least once a year. No problems to report.

Do I think DOT 4 will present a problem: Not really, but if one develops and it's not a mechanical part I'd look to that.

I think DOT 5 fluid is too thin to use/too corrosive.

These are just MHOs.

ZeeOSix

I'm sure DOT 3 was developed before DOT 4, and as such they are the same base and therefore compatable ... but DOT 4 is "enhanced". It's like Dexron fluids, Dexron VI is compatable with all older Dexron versions (ie, Dexron II for example), but Dexron VI is just a better enhanced version of the Dexron fluid line.

j curtiss

Thanks for the response. I remember the old Triumph GT 6 brake master cylinders would absolutely not tolerate any other fluid than Castrol brand brake fluid.

The DOT 3 DOT 4 fluid issue does not appear to be the same as my old Triumph fluid problem. And if Tom and Ray say they're miscible, then by golly they must be. And per Ray's instructions, I made special note not to use Felipo Berio Extra Virgin Olive Oil, as tempting as it is.

So, with DOT 3 and 4 being completely miscible and compatible, I wonder why GM insisted on the warning? Does the C6 have the same warning, I wonder?

BlackZ06

Strangely, in the 2006 and 2007 C6 Owner's Manual, page 443 (2007), the brake fluid listed is DOT3, but the clutch fluid is DOT4 brake fluid ....

see following link for access to C6 owner's manual (just change the year to move between the different manuals ...) ....

https://www.mygmlink.com/pdf/go2cont...07corvette.pdf

TEXHAWK0

Anybody know when DOT 4 first appeared?
Could be in 1999, DOT 4 did not even exist, so the reservoir says used DOT 3.

BlackZ06

Not sure exactly when it came out ... but why does the C6 say DOT3 for brakes and DOT4 for clutch ????? WEIRD ......

Jason

3,4, and 5.1 are all compatable.
5 is it's on animal.

MNCrystalRed2011

NEVER use DOT 5, it is silicone and not compatible with DOT 3 & 4. I use DOT 5.1 in mine.

JPEAK

AU N EGL

Brake fluids classified as DOT3 and DOT4 are naturally hygroscopic: that is, they possess a strong tendency to absorb water. Air can contain varying amounts of moisture depending upon the relative humidity. This moisture can find its way into the brake system through flexible hoses, thus contaminating the fluid. Moisture contamination directly results in reduction in the brake fluid boiling point.

The frictional components in a braking system generate very significant amounts of heat, especially vehicles being operated in severe conditions like a police vehicle or service vehicle in mountainous regions. Vehicles used in operations such as these could have an increase of brake fluid temperatures of as much as 20%. This combination of higher heat and a reduced boiling point increase the possibility of fluid vaporization or vapor lock. Unlike brake fluid, vapors are highly compressible. When brake fluid becomes more compressible it loses its ability to transmit the necessary force to effectively stop an automobile. In the loss of brake force comes the loss of pedal response and conceivably, even loss of braking action. Vehicles equipped with Anti-lock Brake Systems (ABS) are much less likely to skid out of control, especially when the roadway is wet or slippery. The anti-lock system pumps the brakes automatically up to 15 times per second, thereby avoiding brake lock-up and skidding. The results are maximum braking and increased control. ABS systems, in some vehicles, send a sense of reduced resistance to the brake pedal. General Motors, in their Chevrolet Caprices, have added a booster kit to the vacuum booster, which increases the amount of resistance felt in the brake pedal. GM has also added larger wheel cylinders to the rear of the vehicle to create more braking power. This also creates more heat in the brake components.

Conventional DOT3 brake fluids will absorb and average of 2% or more of water in the first year of usage. In that period, the boiling point can drop from 401 degrees to 250 degrees, a reduction of over 150 Fahrenheit degrees.(6) Brake fluid designated a DOT4 possesses an important characteristic, having low moisture activity or improved ability to resist boiling point drop. This boiling point drop becomes essential in assuring safe brake operation.



Brake Fluid Comparison

Brand Wet Boiling Point Dry Boiling Point
Castrol SRF 518°F 590°F
Motul RBF600 420°F 593°F
Wilwood EXP 600 417°F 626°F
AP-600 410°F 572°F
Brembo LCF 600 399°F 600°F
ATE-Super Blue 392°F 536°F
Valvoline 333°F 513°F
Castrol LMA 311°F 446°F
Ford HD 290°F 550°F
Wilwood 570 284°F 570°F
PFC-Z rated 284°F 550°F
AP-550 284°F 550°F


Summary

A number of automobile design changes have occurred in recent years which directly or indirectly affect the braking system. The major influence on design changes has been for fuel economy. Drastically modifying the vehicle aerodynamics and design reduces turbulent air flow under the vehicle to lower the wind drag factor. Unfortunately this also results in a reduction in cooling air past the brake discs and drums. This potentially translates to significantly higher brake fluid temperatures in the wheel area. Improved aerodynamics and engine turbo charging have served to increase under hood temperatures. This will increase the temperatures in all brake components, from master cylinder to the rotors and drums. Front wheel drive vehicles and smaller lower profile tires equally increase brake fluid temperatures.

The boiling point of new DOT 3 brake fluid is 401 degrees Fahrenheit. Contaminates such as moisture, dirt and corrosion greatly reduce the boiling point of brake fluid. High temperatures encountered in ABS disc brake applications require hydraulic fluid specifically formulated to withstand the higher temperatures than normally experienced in drum type brakes. Modern hydraulic brake fluids are designed for high boiling points because of the extended temperature ranges prevalent in disc brake service. Small amounts of contamination such as foreign material, vapor and water greatly decrease the boiling point. When the service temperature exceeds the reduced boiling point, contaminated brake fluid will vaporize and prevent positive braking on the subsequent application. Besides materially reducing the boiling point, moisture promotes rust in
steel brake lines, sludge in cylinders and corrosion inside wheel cylinders and calipers

99 vett babycar

Irish Whiskey

I have used Motul 6 for sometime - good high temp and fine for daily driving

Greg_E

I use the ATE super blue. Good stuff, and more reasonably priced than some of the high end DOT 4 fluids. It also come in the regular yellow color. If you alternate which color you use each time you flush the system it's easy to tell when the old fluid has been purged.

Lord Vetter

Dot4 can be used in Dot3 applications. However, Dot3 should not be used in Dot4 apps.

timemender

The main problem with silicone brake fluid is that it has an affinity for air – it tends to form and hold air bubbles. ABS systems cannot use silicone primarily for this reason.

Years ago, I used silicone (DOT 5) in my C3 Corvettes for a few years for the sole purpose of keeping moisture out of my brake system. Worked like a charm with a good solid brake pedal – until I took one of the cars on a trip over the Appalachian Mountains while traveling to Florida.

Traveling UP the mountain range everything was just fine, however on the way down the change in the ambient air pressure caused air bubbles to form in the silicone fluid. Talk about spongy brakes – I hardly had any stopping power at all.

I use synthetic DOT 4 in all my cars now – C3 – C5 – and others.