No, it says do a full flush of the older fluid and replace it with the new one. No mixing.
Can I use Lucas Synthetic DOT 3 Brake Fluid instead of the Subaru brand DOT 3 on a 2015 Subaru Crosstrek with 92K miles?
- Thread starter Jeep_Riot
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Correct, a full flush....
Most of you have completely missed the point. It's about ratio. You don't mix fluids types because of basic chemistry. There's no hard and fast rule, however... usually... usually.... two differing fluids mixed gain a lower boil-point than any one of them.
Brand A's DOT 3 mixed with Brand A's DOT 4 does not give you the boil-point of DOT 4. More likely lower than DOT 3. And do horrible things to pH.
The only saving grace, your old DOT 3 was so acidic, no matter what the mix is now, it'll be an improvement. And this before we get onto the BITOG misdirected obsession with boil-point when the focus should be pH. The mix will show a pH through the roof. You've now got a stronger acid that'll soak up moisture far faster. Thus you'll have to flush sooner, which likely won't happen.
Don't mix fluid types. And if you must, put a gallon to the job to be sure there's not much of the old left. It'll take a lot to flush the last 2-3%. It's about ratio. One tiny tin won't do it. Then.. and only then do you get low pH and high boil-point.
Else watch the pH go high.
Yes you can mix glycol base fluids, that'll be what it says on the tin. Only unless you watch the ratio, don't. And brake-fluid manufacturers or car manufacturers -when it doesn't serve their interests - are not going to give you a chemistry lesson, and mostly you shouldn't need one.
One take-away - Boil-point is for knuckle-draggers. Boil-point provided you've got DOT standard fluid in a daily-driver will be broadly irrelevant. It's there to sell brake-fluid. What you want is low pH, sadly that doesn't sell brake-fluid. Let the world buy the boil-point, and the pH tear seals.
Most of you have completely missed the point. It's about ratio. You don't mix fluids types because of basic chemistry. There's no hard and fast rule, however... usually... usually.... two differing fluids mixed gain a lower boil-point than any one of them.
Brand A's DOT 3 mixed with Brand A's DOT 4 does not give you the boil-point of DOT 4. More likely lower than DOT 3. And do horrible things to pH.
The only saving grace, your old DOT 3 was so acidic, no matter what the mix is now, it'll be an improvement. And this before we get onto the BITOG misdirected obsession with boil-point when the focus should be pH. The mix will show a pH through the roof. You've now got a stronger acid that'll soak up moisture far faster. Thus you'll have to flush sooner, which likely won't happen.
Don't mix fluid types. And if you must, put a gallon to the job to be sure there's not much of the old left. It'll take a lot to flush the last 2-3%. It's about ratio. One tiny tin won't do it. Then.. and only then do you get low pH and high boil-point.
Else watch the pH go high.
Yes you can mix glycol base fluids, that'll be what it says on the tin. Only unless you watch the ratio, don't. And brake-fluid manufacturers or car manufacturers -when it doesn't serve their interests - are not going to give you a chemistry lesson, and mostly you shouldn't need one.
One take-away - Boil-point is for knuckle-draggers. Boil-point provided you've got DOT standard fluid in a daily-driver will be broadly irrelevant. It's there to sell brake-fluid. What you want is low pH, sadly that doesn't sell brake-fluid. Let the world buy the boil-point, and the pH tear seals.
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Any DOT 3 will be fine. Subaru, Honda and others do not manufacture fluids or filters and a lot of other parts and chemicals, they publish a spec and buy from "trusted vendors".
Very interesting, not so sure it matters as far as US Government standards makes no such distinction.
(all brake fluid is synthetic, the word is used to marketing)
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Used to buy Valvoline DOT 4 by the case when it was on sale for $5.99 a quart at Advance Auto and use it in everything. Now I can't find it under $10 anywhere. Been using the Walmart DOT 4 for $7.97 instead.
