jimxms

Ok, so I've just done a clutch fluid change on my base c6 using the turkey baster method and pumping the clutch over and over again.

I have a tonne of DOT4 PLUS brake fluid left over and wanted to know if there would be any detrimental affect of doing a 'partial' brake fluid swap by simply emptying and refilling the brake reservoir?

At the moment I imagine it has the original DOT3 fluid in there (8 years + 25k old), so its well overdue a change. But I can't be bothered to do a full brake bleed right now.

Can I do a partial change? Maybe even a few partial changes over the course of a few long drives?

WW7

Wow...I just did this same thing last night and had the same thought as you wondering if I could use Dot4 in my brake reservoir instead of Dot3...I decided I would wait until I got some Dot 3 because it said on my bottle that it was compatible with other Dot 4 fluids , but it didn't say anything about being compatible with Dot 3.. Your only talking a few dollars for fluid, so I dicided to wait until I purchased the proper fluid..I decided to just do a complete bleed of the system , that's really the only way to get the old fluid completely out.....WW

I'm sure if you google this question you will get an answer...
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icntdrv55

Yup. DOT3 and DOT4 are miscible with no ill effects. You won't likely see any benefit, tho, as most of the contamination is gonna be at the caliper end, which is also where the heat is coming from. Fresh fluid in the master isn't gonna travel very far down the brake lines when you push the brake pedal simply because there isn't much movement of the caliper pistons and so, not much volume of fluid is exchanged from the master. Can't hurt, I guess.

jimxms

Cool, thanks for the info. I guessed that it probably wasn't going to make much of a difference as the fluid doesn't really circulate. But hey while I had left over brake fluid I thought I might as well.

icntdrv55

FYI. While the benefits of DOT4 over DOT3 are a modest increase in boiling point (BP) WHEN NEW, DOT3 actually retains a greater percentage of it's "fresh" BP index over time as it ages and picks up moisture, while DOT4 degrades more quickly and the BP decreases more quickly with increasing moisture content. This is why most manufacturers use DOT3 in their vehicles' brake systems. If you plan on using your car for HPDE or track, there certainly is some benefit going with a higher BP brake fluid, but there is zero benefit gained under normal street driving conditions.

Note that DOT3, DOT4, DOT4 Super and DOT5.1 are all glycol base fluids and are completely compatible with one another. However, DOT5 is a silicone base fluid and must NEVER BE MIXED with the glycol base fluids!!!

timd38

You can have DOT 3 with a higher boiling point than DOT 4. The range of temps for DOT 3 and DOT 4 are so big that the overlap is huge.

We supply brake fluid to 4 OEMs and a 600 dry, 400 wet to the aftermarket.