99 Honda Odyssey had brake fluid flushed 4700 miles (27 months) ago. The mechanic claims that it is in serious need of replacing due to having 300+ copper parts per million (they were the ones who flushed it last time). If it does need to be replaced now, does that mean they likely did not do a good job last time? Is it expected to have to replace the brake fluid after less than 5K miles, given that it has been 27 months?

Update: the maintenance schedule says to replace the brake fluid every 36 months or 45K miles, whichever comes first. Coupled with other comments, it seems reasonable that I would have to change the brake fluid again.

  • 27 months ago is a long time to only drive 4700 miles. So yes, it would not surprise me if the brake fluid needs to be flushed.
    – jwh20
    Commented Jan 6, 2020 at 23:38
  • Brake fluid absorbs water from the atmosphere. The usual recommendation is to change it every 2 or 3 years whatever the mileage is. Even if you are driving very low mileage, you never know when you are going to need to do an emergency stop!
    – alephzero
    Commented Jan 6, 2020 at 23:50
  • Is he/she giving you some type of test results that indicate it needs to be changed? Refractometer testing, off color, test strip are common tests did they show you results of some testing?
    – mikes
    Commented Jan 7, 2020 at 0:00
  • In UK the mechanic often quotes the "boiling point test" claimed to have been done. When the fluid contains water, as mentioned, it boils at a lower temperature. Commented Jan 7, 2020 at 0:16
  • 1
    Those tests are bs. They always test as having high copper content. I dont even think braking systems have much copper in them. But is the brake master cylinder piston copper? Here's a link for the test kit they used. Phoenix Systems (3003-B) Brake Fluid Test Strips, 2 Strips Per Package, Reveals Brake Fluid Condition amazon.com/dp/B00E6TXWA6/ref=cm_sw_r_sms_apa_i_.TxfEbNGZHQDC
    – Dan Z
    Commented Jan 8, 2020 at 6:52

1 Answer 1


Brake fluid replacement is not determined by the amount miles on the vehicle, but by the amount of time. That's because it is hygroscopic, which means it absorbs water. It does this through the rubber in the lines and anywhere else it can find it.

The normal change interval for DOT 3, 4, & 5.1 is two years. If you're past that point, you should get it flushed with fresh fluid.

I don't know if 27 months is "serious", but your mech is not wrong in that it should be changed. The brake fluid will continue to work even if it is expired. The big deal with brake fluid is, the more water it absorbs, the lower the boiling point becomes. If the brake fluid should boil due to overheating, you can seriously lose braking ability as the steam in the lines will act just like if you had air bubbles in there. Air (or steam) bubbles compress, which means the brakes will be about as spongy as can be.

  • 2
    Some of the commenters above should read this answer...
    – Solar Mike
    Commented Jan 7, 2020 at 8:54
  • The Honda owners manual says 6 years or 90,000 miles unless brake fluid condition required it being changed during prior inspection. The key point being condition of the fluid, which is measurable. My comment was to get a clear reason why the flush was needed. If the fluid is rusty, changing it will not remedy the problem.
    – mikes
    Commented Jan 7, 2020 at 11:36
  • I feel it is amazing to see how the source of the specification can take it from one extreme to the other. Ask a quickie lube oil change place how often and they certainly says 3 months 3000 miles. Ask the salesman at the dealership what the yearly maintenance cost estimates are and you'll actually get stuff like honda recommendations, 7500 miles and the $2.99 USD oil filter EVERY OTHER OIL CHANGE. Insane. Commented Jan 9, 2020 at 0:22

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .