I am not greatly familiar with brake fluids, but from what I have read
you must go with the manufacturer recommendation. You do not replace DOT
3 with DOT 5, etc.

Given that, I would suggest not mixing brake fluid types. You could get
away with topping off 20-50 with 10-40 in your engine oil, but using the
wrong brake fluid is a Very Bad Idea.

Chuck

On 5/4/18 9:27 AM, ddbjorkman@verizon.net wrote:
> Can one mix Dot 3 and Dot 4 brake fluid in a Vanagon brake system, or is that not recommended?
>
> Dave B.