Mixing Brake Fluids?

[sproutdreamer]

I decided to bleed my brakes and at the same time change the fluid as it has never been done on a10 year old Avensis. So being wary of snapping off bleed nopples I gave them a dose of Penetrating Oil a couple of times before the day. All went well and I did get a bit of air out and flushed about 2/3 of a litre through althogether. I was topping up with Halfords DOT4 fluid and finished topping up with Comma DOT4 fluid, however the Comma Fluid is labelled synthetic. Have I boobed by mixing synthetic with non synthetic fluids and am I going to regret it? At the time I was thinking that they were both DOT4 and therefore compatible but does DOT4 only refer to temperature specs?

I am aware that mixing 4 and 5 is a no no as one is Glycol and the other silicon based, just hoping that the Halfords Fluid just does not say synthetic although it is also a glycol base?

[Guest]

On the basis of pure caution, i would drain and replace again.

Its that's just not possible for any reason, your best to check with the two manufacturers of the fluid, as the types can vary substantially.

For example , Motul points out with their fluid:
DOT 5.1 BRAKE FLUID,
QUALITY100% SYNTHETIC, OEM APPROVALS: FMVSS 116 DOT 5.1 NON SILICONE BASE, DOT 4 ET DOT 3 ; SAE J 1703 ; ISO 4925 (5.1, 4 ET 3)
RECOMMENDATIONS
Mixable with DOT 3, DOT 4 and DOT 5.1 NON SILICONE BASE products.
Do not mix with silicone (DOT 5 silicone base) or mineral base fluids (LHM).

Taken from:
https://www.motul.com/us/en-US/products/dot-5-1-brake-fluid
https://s3-eu-west-1.amazonaws.com/motul-production2/images/product_descriptions/technical_data_sheets/2614/DOT_5.1_Brake_Fluid__28GB_29.pdf?1492016150

 

[sproutdreamer]

Just had a look at the Halfords can. It is also Glycol based as is the Comma and the ingredients although not exactly the same wording  very similar so ok I think.

[yossarian247]

Basically DOT4 is DOT4.

Some brands seem to put the word 'synthetic' on the packaging but it is meaningless. One manufacturer's DOT4 will mix fine with another manufacturer's DOT4.