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Re: Why you should change brake fluid periodically
Well apparently GM does as they are one of the OEMs that doesn't recommend changes. Back when I was a Pontiac production engineer in 1968 (during the five year/50K warranty era) I investigated some field failures (not brake related), and the attitude was that they really didn't care about much beyond the warranty period. I think and hope that attitude has changed.
I didn't know that that early brake fluid was a blend of caster oil and alcohol - always thought it was glycol based, but apparently that came later.
Hydraulic systems took a big leap when synthetic elastomers were developed to resist petroleum-based hydraulic fluids and I think the big driver was aircraft control systems circa WWII, but we're still stuck with glycol-based fluid for automotive brakes due to the fear that a switch to a petroleum based brake fluid will be result in the "new brake fluid" being using in older systems designed for glycol, which will likely cause brake failure.
Re: Why you should change brake fluid periodically
I was in an automotive parts store the other day and for the first time saw that Prestone has a synthetic blend DOT3 and DOT4 now. What are your thoughts and information on this fuid?
Re: Why you should change brake fluid periodically
All brake fluids are "synthetic" because they are sythesized in a petrochemical process. Brake fluid, like motor oil should be selected based on specification (API in the case of motor oil, DOT in the case of brake fluid), not brand name.
The primary difference between DOT 3 and 4 is boiling points, although I do have some information that premium DOT 4s may also have a better/longer lasting corrosion inhibitor package even though the basic difference between the two specs is the higher wet and dry boiling points of DOT 4.
I've been using Castrol LMA DOT 4 for at least 20 years, and will probably continue to do so. It's readily available, and I always buy a quart or two for inventory when it goes on sale.
As long as the foil seal is not removed, ASAIK its shelf life is indefinite, but it never sits around more than a couple of years being as how I have three cars that I flush on two year intervals.
Re: Why you should change brake fluid periodically
Thanks for the reply Duke. I also use the Castrol LMA DOT4 and glad to hear that its shelf life is indefinite with the foil seal not removed. Also have silicone fluid in the 68 and 70.
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