I thought someone on this board might know the answer: I have a liter of DOT 4 brake fluid that I bought for my Mercedes, but I also have a Nissan that I want to flush. The Nissan's owner's manual says DOT 3. Can I use the DOT 4 fluid to flush it with? I vaguely remember reading once that you can use DOT 4 in a DOT 3 system, but not DOT 3 in a system that requires DOT 4. Is that true?

Thanks,

GregS