Thanks for the info. I see that I should have been more specific about the brake fluid I am considering changing to. I am looking at Valvoline SynPower Dot 3 & 4 spec with synthetic formulation. Currently, I use Pentosin Super Dot 4 but my supply is almost gone. Hence, the inquiry/question about synthetic (Valvoline) versus non-synthetic (Pentosin) brake fluids. Also, the Valvoline brake fluid costs about 40% less ($5 vs. $8.25) than Pentosin not including S&H to have the Pentosin sent to me. Additionally, if the Valvoline is superior to Pentosin regarding moisture absorbtion then I would change despite the fact that the Pentosin has worked for me for many years. I am always looking for improved products to use as technology/research provides upgrades - provided the new product is proven to be better and not just hype.

I do understand that the Dot 4 synthetic brake fluids do absorb moisture, but at a lower rate which should extend the period when the fluid needs to be changed (up to perhaps 2 years?). Am I right or wrong?

I also change my brake fluid when the relative humidity is low - like after a cold front comes through and the RH is about 25% or less. In Texas, that means the best time to change the brake fluid is just around the corner.

I did not even consider Dot 5 silicone based brake fluid. I have known about the problems with this product for some time - but thanks for reinforcing my knowledge/position as it has been a number of years since I last looked at Dot 5 silicone based brake fluid. However, Dot 5 does have it's advantages but I do not believe my needs requires the use of Dot 5.

Tom