Brake Fluid. Moisture Content. Change Intervals.

[koko64]

Changed the brake and clutch fluid on a 749S six months ago. Used a reputable local brand of DOT4 (Penrite). Flushed and bled carefully using a number of methods but an electronic fluid tester recently indicated that the fluid had too high a moisture content (fail). Did it all again with Castrol DOT4. I actually tested the new bottle after opening and although passing, the device indicated a low level of moisture content.
Although the bottles have an inner seal under the cap there must be a negligible amount of moisture in the air gap between fluid and cap. The device i purchased is new and used in many workshops. It's a pretty sensitive device!

A rule of thumb for street bikes is to change brake fluid change every 2-3 years. Areas with high humidity may be every two years.

Any comments or insights much appreciated.

For reference.
https://www.misco.com/when-to-change-your-brake-fluid/

[Howie]

Shocking!

I've always change fluid on bikes yearly and cars every two years and use an extra high boiling point DOT 4 like ATE 200.

[DarkMonster620]

I always changed my brake/clutch fluid on the bike every 18 months, yes, that much humidity and in my car, every 2yrs ... As well as coolant, NO exceptions ... Yes, avg humidity 70% and those seals in MCs, just don't trust them, I have just replaced my car's brake reservoir's cap on last fluid flush made.

[stopintime]

The very best Castrol (boiling point 70 degrees higher than number two) three years ~ 40,000km. Neither bottle or bike reservoir any sign of humidity. Cheap tester.

[koko64]

The moisture content was verified by my local car shop with a premium Wurth device. The car shop is a certified vehicle tester and my device (Repco) had the same reading. So the new fuid (Castrol) passed but still registered a small % of moisture below the threshold (<1%). The devices are therefore very precise and sensitive.

[koko64]

I always changed my brake/clutch fluid on the bike every 18 months, yes, that much humidity and in my car, every 2yrs ... As well as coolant, NO exceptions ... Yes, avg humidity 70% and those seals in MCs, just don't trust them, I have just replaced my car's brake reservoir's cap on last fluid flush made.

Interesting. Melbourne's summer has had tropical humidity this year and a very high dew point. The customer's bike was sweltering in a tin shed. Might have to change to Panama specs.

[DarkMonster620]

Interesting. Melbourne's summer has had tropical humidity this year and a very high dew point. The customer's bike was sweltering in a tin shed. Might have to change to Panama specs.