Brake Fluids (A hopefully definitive thread)

[cheezemonkhai]

Following much discussion about brake fluids i figured a mini thread to pull together the information and keep it somwhere useful it can be found was called for.

So to summarise you have the following brake fluids that you can readily buy:

• DOT 3
  
• DOT 4
  
• DOT 5
  
• DOT 5.1 (Also knows as Super DOT 4 or DOT 4 Plus)
  
• LHM
  

DOT 3, DOT 4 and DOT 5.1 are all compatible and as such can be 'mixed'

DOT 5 is silicon based and MUST NOT be mixed with any of the other fluids.

LHM this is mineral based and is only for use in citroens with the hydraulic suspension (or rolls royce cars with the same set up). This MUST NOT be used in place of a DOT rated brake fluid.

Super DOT 4

To summarise super DOT 4 is another name for a fluid which meets or exceeds the DOT 5.1 standard.

DOT 5.1 fluids are simply DOT 4-type fluids which meet DOT 5 performance requirements and because of this, they typically can be mixed with DOT 3 or DOT 4 fluids without concern.

The referal of these fluids as ‘DOT 4 Plus’ or ‘Super DOT 4’ fluids is done because they are more similar to a conventional DOT 4 fluid by chemistry than they are to a conventional DOT 5 fluid. In fact, DOT 5.1 is essentially comprised of Borate Esters

This information was taken from product data sheets and the article at:

StopTech : Balanced Brake Upgrades

Which Brake Fluid

Generally DOT 4 will suffice for your car, however should you intend to be driving in a brisk fashion then DOT 5.1 may be a better choice due to the higher dry and wet boiling points.

The wet boiling point is what is important, as after the fluid has been in the brake system for a year this is most likely how the fluid will behave in real use.

Some car suppliers (including halfords) recommend DOT 5.1 fluids for any cars which use standard DOT3/4 fluids and have ABS.

[john_grant358]

Good thread, nice one!

[drew79]

DOT 3, DOT 4 and DOT 5.1 are all compatible and as such can be 'mixed'

I just wanted to make it clear that you can mix them, but only go upwards in numbers from what you have otherwise you will lower the boiling point...

So if you have some old classic motor that says use DOT3 you can stick in DOT4 or 5.1... but dont go sticking DOT3 in a modern motor.

Most VAG motors from late 90's onwards will all specify DOT4 plus, I know it can be tricky to find in the shops but I personally wouldn't risk anything else brakes are concerned.

I dont know if they specify DOT4 plus due to the higher temps found inside the calipers of modern braking systems, or if its more to do with high temps found inside the ABS pump due to the pressure when the ABS kicks in.

[billly the fish]

HI,

You seem very clued up on brake / servivce i have a fabia 1.9 tdi est 2001 It recommends oil to be changed every 10k, / brake fluid every 24 month is this essential AS I ONLY COVER 6/8K a year mostly short runs scchool runs,max run around 70 miles every fortnight when we go to the caravan, the car has main dealer full service history and the oil was changed at 77k also brake fluid part of 12 month annual inspection purchased at 86k, now at 88k,

Thanks,

Billy the Fish.