My shop manual and master cylinder reservoir cap call for DOT 4 brake fluid for my '92 Volvo w/ABS.

But I can't find any straight DOT 4. The only fluid I can find around here is straight DOT 3 or a kind of a fluid that claims it "exceeds DOT 3 and DOT 4 and can be used in place of either." I found both NAPA and Castrol in this DOT 3/4 version.

Is this 3/4 fluid OK to use? Would it be better to wait and order some straight DOT 4 fluid like ATE? (Or is ATE fluid 3/4 too???)


Also, this 3/4 fluid says it "is compatible with conventional fluids". Does this just mean this fluid will work with any other brand of fluid, or does it mean this fluid is some other formulation?

TIA
Dave S.

DOT4 and DOT3 are actually rather similar, and it's usually no problem using DOT4 with or in place of DOT3. While I wouldn't necessarily trust something making these claims if it were sold in white containers from the back of a truck at a swap meet, I think that if a well-regarded brand like Castrol sells it it's very likely to be fine. If it was problematic I think the DOT would be on their case rather rapidly.

The stuff that can be problematic is silicone DOT5.

I would assume "compatible with" to mean just that -- regardless of what's in there, it's been tested to play nice with DOT3, DOT4 and the related seals.

Most DOT4 on the market exceeds the minimum DOT4 specs, so I wouldn't be surprised if what's in those containers is actually the same stuff that used to be sold as DOT4, rebranded to eliminate the need to keep DOT3 (really a niche product these days) in the product range.

I wouldn't hesitate to use it.

Bram