DOT-3 vs DOT-5 problem. Got them mixed.

From: Bjorn Brandstedt (super_deuce@hotmail.com)
Date: Sat Nov 09 2002 - 03:41:30 PST


Some thoughts about brake fluids.

It is interesting to note that the manual for Battlefield Damage Assessment
and Repair (TM 9-2320-356-BD), lists the following emergency substitutes for
brake fluid: Hydraulic fluid, Antifreeze, Diesel fuel, Water,
Petroleum-based fluids and Alcohol. Of course these are only temporary
measures, but they make a hydraulic system consisting of non-compressible
liquids.

Fact:When you accidentally add DOT-3 to DOT-5, you still have a complete
hydraulic system. The brakes will not fail. Most brake systems probably end
up with some water in them as a result of condensation (the master cylinder
is vented and exposed to the ambient air at all times), but the system still
works just fine with those two fluids. In the long run, there may be some
corrosion. This corrosion is more of a problem with DOT-5 since water may
collect at low points. Remember that the truck was designed for DOT-3 fluid
and water mixes with DOT-3 but not with DOT-5 and seals etc are compatible
with DOT-3 for sure.

Question: What is the real reason for using DOT-5 in MV's?
Personal opinion: DOT-5 was specified because it does not act as a paint
remover when spilled.

Fact:When you pour DOT-3 fluid into a reservoir with DOT-5, then the DOT-3
sinks to the bottom, the fluids do not mix, but you still have a hydraulic
system of non-compressible fluids.
Assumption:There may be some problems at the extremes when the differences
in boiling points come into play, but having water in the system would be
more of a problem with its lower boiling point.

Question: Would this statement be correct? "As long as the fluids are not
brought to a boil (from extreme driving, mountains etc), there is no reason
to be concerned when there are more than one type of fluid in the hydraulic
(brake) system".

Bjorn

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