Need answer ASAP about brake and Power steering fluid

[CL8]

Are brake and power steering fluid the same and can one be used for the other?

Why or why not?

Thanks
cl8

[MagicRat]

No. They are, chemically, very different and must never be mixed, ever, or component damage will result.

Brake fluid is based on ethylene glycol (except for DOT 5 fluid, which is silicone based). If used in a PS system, it will not lubricate the hydraulic moving parts like the PS pump sufficiently. Also PS systems are not well-sealed by design, so the fluid would become contaminated by moisture.

Hydraulic fluid is usually petroleum-based, and will ruin the flexible seals found in a brake system.

[CL8]

Thanks MR,

I remembered a driving instructor I used to work with said something to that effect, (her brother was a mechanic)
and tomorrow I am going over fluids under the hood with drive students.

Interestingly, brake and power steering fluid are very much the same color, any reason why?

And is there ANY automotive fluid that could be used in place of another?

My guess is there is not, I am just trying to find out if this former co-worker was talking about two other kinds of fluid.

Thanks,
Cl8

[Moppie]

Power steering and fluid used to be the same as automatic transmission fluid, since its just a lubricating hydraulic fluid.
They were all red.

Then for some reason it seems that manufactures have started specifying a different fluid for the power steering, which is usually clear.

So older cars generally use the same fluid, while newer ones seem to use different fluids, and there are cross of vehicles that are supposed to use different fluids, but work just fine on the same fluid (late 90s Honda's for example).

[RahX]

Brake fluid will outrageously swell a petroleum seal the same way petroleum will a brake seal.

[CL8]

Thanks Moppie and Rahax!

[MagicRat]

Originally Posted by CL8

Interestingly, brake and power steering fluid are very much the same color, any reason why?

Liquids that do not have dyes or particles in suspension tend to be reasonably clear. It is not deliberate but merely a byproduct of chemistry.
For example, gasoline and water initially appear to be almost identical, but obviously are not.
Auto transmission fluid is red because it has been dyed, for identification purposes. Without the dye it is clear, like hydraulic fluid, as far as I know.

Originally Posted by CL8

And is there ANY automotive fluid that could be used in place of another?

In an emergency, you can interchange engine oil, power steering fluid and auto transmission fluid (ATF) extensively. Generally, you only would "top-up" the existing fluid, and only in an emergency, if you absolutely have to. But do not replace all of the fluid in a system with a substitution.

You can top-up the engine oil with ATF or PS fluid. You can use ATF or engine oil in the PS system, and use PS fluid in the transmission.

You can use ATF or engine oil in manual transmissions, 4x4 transfer cases and differentials (indeed, one or other of these fluids are specified for some of these devices.)

You can use differential gear lube in many manual transmissions and transfer
cases ( it is required in some types of gear boxes). But gear lube is no good for engines and auto transmissions.

If you do have to mix fluids, it's probably a good idea to get the mixed fluids drained and the proper fluid put in as soon as reasonably possible.

[CL8]

Originally Posted by MagicRat

Liquids that do not have dyes or particles in suspension tend to be reasonably clear. It is not deliberate but merely a byproduct of chemistry.
For example, gasoline and water initially appear to be almost identical, but obviously are not.
Auto transmission fluid is red because it has been dyed, for identification purposes. Without the dye it is clear, like hydraulic fluid, as far as I know.


In an emergency, you can interchange engine oil, power steering fluid and auto transmission fluid (ATF) extensively. Generally, you only would "top-up" the existing fluid, and only in an emergency, if you absolutely have to. But do not replace all of the fluid in a system with a substitution.

You can top-up the engine oil with ATF or PS fluid. You can use ATF or engine oil in the PS system, and use PS fluid in the transmission.

You can use ATF or engine oil in manual transmissions, 4x4 transfer cases and differentials (indeed, one or other of these fluids are specified for some of these devices.)

You can use differential gear lube in many manual transmissions and transfer
cases ( it is required in some types of gear boxes). But gear lube is no good for engines and auto transmissions.

If you do have to mix fluids, it's probably a good idea to get the mixed fluids drained and the proper fluid put in as soon as reasonably possible.

Then for some reason it seems that manufactures have started specifying a different fluid for the power steering, which is usually clear.

So older cars generally use the same fluid, while newer ones seem to use different fluids, and there are cross of vehicles that are supposed to use different fluids, but work just fine on the same fluid (late 90s Honda's for example).

So then, is the reason they started specifying different fluid, for financial profit or because the systems are built different?

[MagicRat]

Originally Posted by CL8

So then, is the reason they started specifying different fluid, for financial profit or because the systems are built different?

Haha.... I think if auto engineers were that financially sophisticated, they would make their living on Wall St. and not in a lab.

You are mixing the marketing concept "product differentiation" with engineering specifications.

All these basic fluids are engineered to excel at certain functions so they all are different, according to their requirements. All packaging and labelling must be justified and accurate. The Society of Automotive Engineers (SAE International) is the industry regulating body which establishes the performance standards and specifications which many (if not all) these fluids must meet.

So, all fluids must be manufactured to meet certain impartial, industry-wide standards and content regulations before they can be sold

I do not think some fluid additives are SAE regulated, though (like fuel injector cleaner, oil additives etc)

[CL8]

Originally Posted by MagicRat

All these basic fluids are engineered to excel at certain functions so they all are different, according to their requirements. All packaging and labelling must be justified and accurate. The Society of Automotive Engineers (SAE International) is the industry regulating body which establishes the performance standards and specifications which many (if not all) these fluids must meet.

Are they for or against Obama?

That will say a lot!


* I finished teaching my class Friday (One kid is born and raised in Saudi Arabia because his dad works for an oil company!)

I didn't tell them to mix ANY automotive fluids.

[jdmccright]

Each fluid type is designed for the environment and conditions in which it is expected to serve.

Oil contains detergents and additives to help with lubricity, prevent drain back (to keep parts lubed upon restart), and to suspend fine particles, all at high temperatures and shear loads. The multi-grade viscosity allows it to work in a wide temperature range.

Brake fluid doesn't need all that, but does need to be stable, be able to prevent corrosion as water is absorbed, and remain a liquid at high temperatures with low vapor pressure. Its low viscosity keeps foot pedal pressure low and valve sizes smaller.

Transmission fluid must hold particle fines, withstand continuous shearing (in the torque converter), disperse heat, and provide lubricity at fairly high, and low, temperatures.

Gear oil must withstand extreme pressure and shear to maintain a continuous film on the gear tooth flats. Its higher viscosity provides this while keeping fines in suspension and prevents corrosion.

I'm sure there are other characteristics unique to each fluid, but this is enough to see that no single fluid can do all these varying jobs. While it would be fantastic to need to stock only one universal fluid, we haven't gotten there yet...indeed, the stock of fluids needed will likely only grow as they become more specialized and demands on those systems increases with new technology.

Hope this helps!

[CL8]

Great points jdmccright,

Isn't one of the purposes of engine oil to disperse heat like transmission fluid does?
I know it does help keep the engine cool.

[jdmccright]

Ayup, it does that and is cooled some by the oil pan in contact with the airstream underneath as well as the cooler in the radiator, but it is augmented by the cooling system.

The coolant, which I didn't even list, has to remain a fluid in a WIDE temperature range, provide lubricity, have high heat capacity, and prevent corrosion of many different materials it is in contact with.

I knew I would miss stuff. Hence the sort-of disclaimer: "I'm sure there are other characteristics unique to each fluid". Thanks CL8.