Brake Fluid

[alhendo1 3,031]

Good morning folks. Possibly a daft question but here goes... I'm going to change the CB500X brake fluid and was in Halfrauds earlier....they had Comma Dot4(which was marked Synthetic) and Mobil which was just branded as Dot4... Are all Dot4 fluids synthetic? and safe to use on the bike....thanks.

 

[Tex 36,817]

I was under the impression that Dot 5 was synthetic and the standard 4 wasn’t, but that’s clearly out of date.

 

Me? I would go for the Mobil. When you bleed brakes you never quite get all the old fluid out and I wouldn’t be wanting to mix synthetic and mineral. Same as you can’t just change to Castrol R, you need a complete strip down and clean. 

[Xactly 5,340]

DOT4 and DOT5.1 are glycol based and may be mixed. DOT5.1 has a higher boiling point. DOT5 is silicone based and must not be mixed with either DOT 3,4 or 5.1. AFAIK any DOT4 may be mixed with another DOT4.

[Andy m 23,473]

Nothing wrong with the Comma IMHO, so long as you stick to the right grade it's all the same. Comma was Exxon until 2012 when they were spun off to their own Brazilian distributor. They are still big enough get good stuff at decent prices so don't need to shift Chinese rubbish. 

 

No idea why they would market one as synthetic though. All DOT4 is from chemical factories, its only sold by the oil companies to complete their offering of all the fluids for your vehicle. 

 

Andy

[Tex 36,817]

12 hours ago, Andy m said:

Nothing wrong with the Comma IMHO, so long as you stick to the right grade it's all the same.
 

 

Indeed. I use Comma oil in my petrol Fiat and in my diesel, er, Fiat. And I will be using it in the wife’s petrol Toyota come January. As good as anything. The only reason I suggested Alan use the Mobil brake fluid was the strange ‘synthetic’ label on the Comma. Maybe it’s a case of marketing (“The punters think synthetics are better”) that’s cost them a sale? 

[alhendo1 3,031]

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.commaoil.com/passenger-vehicles/products/view/197&ved=2ahUKEwjExrDg5LzzAhUqQkEAHSTtCJ0QFnoECBAQAQ&usg=AOvVaw0X8qjsxW1mvw_pZs0XodU5&cshid=1633763989172

I should have probably done this in the first place..... Doh!.... Turns out it can be mixed safely.... Anyhoo, I was in Toolstation last night and bought some Prestone Dot4 so I'll crack on with that. Thanks for the replies folks. 

Edited October 9, 2021 by alhendo1

[MatBin 5,080]

Use whatever grade the manual says, don't put dot5 in if it says 4 or vice versa.

[Hickky 3,131]

I hear brake fluid is hydroscopic, and water is not compressible, therefore what possible harm can water do?

[Andy m 23,473]

2 minutes ago, Hickky said:

what possible harm can water do?

 Except turn to steam which has some really bad volume related habits when heated, condensed or subject to changes in pressure?

 

Andy

[Hickky 3,131]

6 hours ago, Andy m said:

Except turn to steam which has some really bad volume related habits when heated, condensed or subject to changes in pressure?

 

Andy

It was only said in jest mate, keep your hair (or wig) on!

[MatBin 5,080]

15 hours ago, Hickky said:

I hear brake fluid is hydroscopic, and water is not compressible, therefore what possible harm can water do?

Engine oil isn't hygroscopic, so use that instead. Not sure what hydroscopic is though.

Edited October 11, 2021 by MatBin

[Hickky 3,131]

5 hours ago, MatBin said:

Not sure what hydroscopic is though.

Hydroscopic means it attracts water and the water incorporates into the brake fluid. That's why you need to drain then refresh with new on a regular basis. You should never use fluid that has stood on a shelf unless it is under 1 month old and has been stored with a tight cap. Never use old brake fluid, it is cheap and you should never give your life away cheaply. 

[ChrisCB 6,653]

Hydroscopic means absorbs moisture from the air, in the case of brake fluid and air conditioning systems it is absorbed through osmosis from the rubber brake lines and AC lines when the pressure is higher on the inside of the system compared to the outside.

[baben 11,698]

Apparently foxes like to drink it. There has been an outbreak in London of foxes chewing through brake pipes to get at the stuff. Gotta be some jokes in there somewhere for you lot.

https://www.express.co.uk/news/uk/379982/Foxes-drink-my-car-brake-fluid

Edited October 11, 2021 by baben

[ChrisCB 6,653]

3 minutes ago, baben said:

Apparently foxes like to drink it. There has been an outbreak in London of foxes chewing through brake pipes to get at the stuff. Gotta be some jokes in there somewhere for you lot.

https://www.express.co.uk/news/uk/379982/Foxes-drink-my-car-brake-fluid

Makes you wonder how they can identify brake parts in the first place!! 🤔 

 

Also brake fluid is a bigger culprit of under bonnet fires than petrol.

 

[Xactly 5,340]

1 hour ago, Hickky said:

Hydroscopic means it attracts water and the water incorporates into the brake fluid. That's why you need to drain then refresh with new on a regular basis. You should never use fluid that has stood on a shelf unless it is under 1 month old and has been stored with a tight cap. Never use old brake fluid, it is cheap and you should never give your life away cheaply. 

I think Matbin was saying that the wrong word has been used. He's right. I noticed it too, but didn't comment. The correct word is hygroscopic; a hygroscope is something else entirely.... Just saying; it's a common mistake.

[Xactly 5,340]

Sorry I mean hydroscope - predictive text gets its knickers in a twist too...

[MatBin 5,080]

59 minutes ago, Xactly said:

I think Matbin was saying that the wrong word has been used. He's right. I noticed it too, but didn't comment. The correct word is hygroscopic; a hygroscope is something else entirely.... Just saying; it's a common mistake.

I was just being a pedantic old git

[Xactly 5,340]

5 hours ago, MatBin said:

I was just being a pedantic old git

Well, I wasn’t going to say it……

[Hickky 3,131]

Both Hydro and Hygro have the same root in the Greek for wet or moist being hygros. As in middle English a d and a g were often swapped, I just come from a more classical education than you pedants. (and if you believe that, you'll believe anything!)

[MatBin 5,080]

7 hours ago, Hickky said:

Both Hydro and Hygro have the same root in the Greek for wet or moist being hygros. As in middle English a d and a g were often swapped, I just come from a more classical education than you pedants. (and if you believe that, you'll believe anything!)

Cobblers! 

https://www.thoughtco.com/definition-of-hygroscopic-605230

[Hickky 3,131]

On 12/10/2021 at 20:24, MatBin said:

Cobblers! 

Oh well, I tried!