Morris Minor Owners Club

Does anyone know if all DOT 4 brake fluids are compatible?

I was about to top up my reservoir from a new bottle of Comma DOT 4 when I noticed it said ‘synthetic’ on the bottle, whereas the previous TRW bottle said just DOT 4.

Looked at a bottle of Mobil DOT 4 in Halfords – no mention of synthetic or otherwise on the label (no point in asking the staff!).

Searched the web but couldn’t find a clear answer – only warnings that synthetic brake fluid should be used only after rebuilding all the brakes and flushing out the system.

Is all DOT 4 synthetic or is there such thing as DOT 4 non-synthetic?

All brake fluids are 'synthetic' - it will be fine. What you MUST NOT use is 'silicone' brake fluid - DOT 5.

What does DOT stand for?

It cannotbe Dept of Transport as it is sold as such also over here.

It has been accepted as a Worldwide term but originates from the USA "Department of Transportation".

bmcecosse wrote:All brake fluids are 'synthetic' - it will be fine. What you MUST NOT use is 'silicone' brake fluid - DOT 5.

That's just an opinion Roy, I say that because I've used silicon for 15 years with good results, and so far no wheel cylinders seizing etc. As a bonus it's kinder to paint. I realise it's one of your pet hates!

I thought it was obvious - but I meant that DOT 5 Silicone MUST NOT be used in a system running on DOT 3/4 fluid. Simples !

Yes sorry, that will teach me to read posts properly ------ but do lay off the simple with an s on the end!

Sorry....