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Is there a difference between dot3 and dot4 brake fluid?

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Iv'e found some dot3 brake fluid in the shed and i'm wondering if it's similar to dot4 so I can use for my front brakes. The manual said to use dot4 but would dot3 work?

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There may be a difference in boiling temperatures. Most DOT 4 fluids have a higher boiling temp than DOT 3, however they are both compatible. If the brake fluid has been sitting around opened for a long time, don't use it as brake fluid is hygroscopic (absorbs water).

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both should be Poly glycol

boiling point, dry first, then contaminated/Wet

DOT 3 401ºF 284º F

DOT 4 446º F 311º F

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I have used DOT 3 in my bike's brake lines and not issues....now on my sportbike is a whole different beast. DOT 5.1 since these bad boys like to get hot going into corners.

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I would recycle the old brake fluid. Like everyone else pointed out, it will absorb moisture so run down to the local auto parts store, pick up a new container and bleed the brakes with that. Its less that $5 for enough to bleed front/rear brakes on your bike and top off the fluid in your truck.

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