I have 1994 Ranger which wants DOT 3 brake fluid. I went to the parts store today and all they had was the house brand (O' Reilley) and Prestone DOT 3 which had "Synthetic" written all over the bottle.

Seems like brake fluid is hydraulic fluid which is oil after all. So, maybe synthetic's supposed to be better just like for motor oil. It was not expensive at all.

I'm guessing DOT 3 is DOT 3, but I thought to post and ask the experts.

 

Since it is quote synthetic dot 3 it is probably ok . Dot 3 to dot 3. But i am a little goosey about mixing different brake fluids. The O'reilly's house brand will work just fine. And is probably cheaper. If you are going to use the synthetic then I would flush the entire systemand refill the whole thing with the new fluid.

 

It is more than ok, it is recommended. The synthetic fluid can withstand more heat, it lasts longer, it protects the seals better, etc. You can use DOT 4 synthetic too, its even better.

 

However, do NOT use DOT5 brake fluid. It is silicone-based and NOT intended to be mixed with DOT3 or DOT4. It is an animal unto itself and is used ONLY in those vehicles that specify it.

 

The only advantage other than a lower boiling point would be the elimination of alcohol in the mix which would stop the wicking of moisture from the air. Other than those two factors there really is nothing wrong with DOT 3. It has been around for a long time and still works. I've never had it hot enough that it didn't. As far as DOT5 conversion. I worked for the largest fleet in the US when they went that route and even following all the instructions it was a bit of a nightmare. kotzy

 

So what is the difference in dot3 and dot4? Why do new cars still call for dot3?

 

Dot 4 is used mainly in older cars [MG's and Triumphs come to mind]. They used a live rubber [not synthectic] for their seals. I learned the hard way many years ago that Dot 3 is incompatibale with 'real' rubber. Modern seals are made from oil, not rubber trees. My British cars could use Dot 5 but it was far too much trouble purging the brake and clutch lines. I simply stuck with Castrol LMA Dot 4. I could also use it in my American cars and trucks with no problem. I never had a problem mixing them. Indeed, all I kept around my garage was Castrol.

 

My VW Passat uses DOT4. Seems the moral of this story for me is to use exactly what the manufacturer recommends for the car.

 

I'd use Motorcaft DOT-3 fluid, as it's formulated for our brake systems & is a very good product with a very high boiling point.

Maybe this link to a mini brake fluid tutorial would be informative, it sure was for me.
http://www.aa1car.com/library/bfluid.htm

Answered questions about why not to use silicone brake fluid on street vehicles, why DOT-4 fluids loose their boiling point faster than DOT-3, it has a boilng point curve versus time, so we can see where we likely are on the boiling point curve, with our old brake fluid thats absorbed moisture over the past years & how to test brake fluids boiling point.

I change/flush my brake fluid evry 3 years with Motorcraft fluid, because we haven't lived until we have to fork over a chunk of our gold for a ABS system motor thats all sludged, or corroded up from old moisture contaminated fluid!!!!