[Tigers] brake fluid - Types

[Rense, Mark (GE Indust, ConsInd)]

The main difference between DOT 3 and DOT 4 (both glycol-based) is the boiling
point. The DOT 4 has a higher boiling point for both wet and dry measurements.
This is important to us because our clutch and master cylinder reservoirs are
not sealed and therefore allow the passage of moisture, and since glycol-based
fluid is hydroscopic, the DOT 4 rating will allow more moisture content while
still providing adequate service.

You CANNOT mix DOT 3 or 4 with DOT 5, as DOT 5 is silicon based. However, you
can mix with the new DOT 5.1 fluid. The recommended fluid for most British
cars old and new is Castrol GT/LMA, which is rated as a DOT 3/4. If you
rebuild your hydraulics with all new synthetic rubber parts, you can use the
silicon-based DOT 5, the advantage here is that when (notice I didn't say
"if") it leaks, it does not affect the paint. The disadvantage of DOT 5 is
that it does not absorb water at all, so the water pools in the cylinders and
causes corrosion.

In any case, flushing your brake fluid every other year is a Best Practice.

Brake Fluid Rating  	Dry boiling point		Wet boiling point
DOT 3 			2050C (4010F) 		1400C (2840F)
DOT 4 			2300C (4460F) 		1550C (3110F)
DOT 5 			2600C (5000F) 		1800C (3560F)
DOT 5.1 			2700C (5180F) 		1910C ( 3760F)

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