Brake Fluid

[culzean]

Just changed the brake and clutch fluid on Civic, Jazz will be next to get done.  Use a MityVac and makes the job a doddle,  jacking up car and getting the wheels off is the hardest part.  It helps if clean around nipple and take it out and put a couple of wraps of plumbers teflon tape on the thread nearest hexagon,  then it sucks fluid and not foam due to air getting around the thread.  Last time I did brake bleeding I found some thick 'O' rings that were a tight fit on nipple thread and they did the job of stopping air, but the brake fluid attacks then and they crumble away before you can get the benefit of them next time.

There are two types of DOT 4 standard and ESP, the ESP is designed for use in vehicles with Electronic Stability Program and from what I can gather is a higher quality / lower viscosity fluid than standard DOT3 / 4.  Just to muddy the water some brake fluid makers label their fluid 'synthetic' but as they are based of Glycol Esters they are all synthetic ( ie. man made and not naturally occurring ).   For some reason DOT 5 is silicone based but DOT 5.1 is glycol based - confusing or what, the main difference between DOT 3, 4 and DOT 5.1 is the boiling point.

Anyway,  because the Civic and MK2 -> Jazz have VSA  ( Honda Version of ESP but labelled Vehicle Stability Assist ) which can selectively apply the brakes on each wheel to stabilise the car during a skid I used the DOT 4 ESP brake fluid ( Mobil ) - the ESP fluid is supposed to make the ESP / VSA more effective - but the Jazz Handbook makes no mention of it, just says DOT 3 or 4 fluid.  ESP fluid is only a couple of £'s more expensive which over 3 years is not a lot.

Is ESP label just for marketing. like the 'synthetic' labeling   If it had been twice the price may have thought about it, but £9.50 instead of £7.50 for 500ml is hardy a deal breaker.

[MicktheMonster]

I might be wrong but I was under the impression that the ESP stuff has a higher boiling point, meaning it will keep working for longer under harsh use (such as prolonged maximum pressure), so it probably is worth the extra if you ever need it in an emergency.

[culzean]

From what I have read as the number goes higher the boiling point goes higher.  The 'dry' boiling point is for fresh fluid, the 'wet' boiling point is when fluid has 3.5% absorbed water content.  DOT 3 is lowest boiling point, DOT 4 is higher and DOT 5.1 is highest ( they are specified by department of transport to have a minimum boiling point but some makers exceed that specification ) as I said, ESP seems to be lower viscosity and more stable viscosity for use in vehicles that have electronic stability program / or what Honda call VSA which can selectively use brakes to help you out of a skid and also cut engine power if it senses a skid. The lower viscosity is designed to speed up the response of the stability control selectively applying brakes on and off to control skidding.

Thought if anyone was thinking of replacing brake fluid the information may help..

The brake fluid was changed a couple of years ago and was hardly any darker than the new fluid,  the clutch fluid has been in since Civic was new ( 7 years ) and was a lot darker colour.  The sealing that Honda use on reservoir caps looks well designed to stop moisture getting in that way, but apparently water molecules can pass through the flexible hose material and also around piston seals. 

I thought they had announced a few years ago that moisture content of brake fluid was going to be checked as part of MOT,  but according to attached article they only check level and it says ' reservoir caps should not be removed '.... but there is a note nearly at bottom of article  to say 'contamination of brake fluid' is a major fail - do they just check the colour of fluid through transparent reservoir ?

https://www.motester.co.uk/mot-test-of-brakes/