5.1 has a higher boiling point than silicone too.

i found this info in my documents-----

Brake fluid is engineered to do specific things in specific ways. So it's important to put the right kind in your car or truck.

DOT 3 and DOT 4 brake fluids are glycol-based. They're used in most modern cars and trucks, because they work with ABS brakes. DOT 4 has a higher boiling point than DOT 3. You can use DOT 4 where DOT 3 is called for, but not the reverse. Using DOT 3 in a DOT 4 brake risks boiling the brake fluid. Glycol-based fluid can absorb water over time, which leads to corrosion. It also changes the quality of the fluid in braking. This is one reason to have your brake fluid changed regularly.

DOT 5 is silicone-based. Its advantage is that it doesn't absorb water, so it doesn't corrode brake systems. However, it doesn't work with ABS brakes. So it's mostly for older cars and trucks.

I saw a video of dot 5 swelling seals is that true.? That's the only reason I have been hesitant to use it.

I totally understand the paint issue, but as long as you don't use a squirt pistol to add fluid I would just be careful. Talk to strange, mark williams, or wilwood they all recommend 5.1.

I have been using Dot 5 in my all cars for at least 30 years, have it my '70 Roadrunner that is in that 30 year range, drained some at all the 4 corners a few years ago and it still had a bit of that purple look to it. The reason I went to Dot 5 30 some years ago is that after 2-3 years of Dot 3 fluid I was having brake leakage from the wheel cyls due to rusty bores, I live where we have that good old white crap, in the snow belt for 1/2 a year. Not to mention it doesn't destroy your paint!!!I I also have it in different year Vipers, '02, '03 with ABS and no problems.

If this was true then that means it would/could cause brake failures. Can you imagine the legal liability for someone selling a product, that if misused, could kill you?

What is interesting about this whole question is that when this came up 10 years ago or more, the majority said don't use it. Its good to see "we" have become more informed.

some years back I saw or read something about dot 5 swelling seals/rubber stuff. i'd been using dot 5 on one of my cars for several years and thought i'd better check this out. it was complete bunk. no damage and everything was as good as the day it was installed. I don't understand the anti dot 5 thing. I probably have close to 25yrs on the brake system with dot 5 and the car has never stopped better.

The reason I have wanted to do this was I have a charger and belvedere that sit for long periods and i have had rusty seepage from the master cylinder pushrod area that eventually eats all my firewall paint below the master. If this would stop that it would be great!

go for it. your reasoning is the same as mine. both my cars are fine with dot 5.

So just drain as best I can and refill?

you need to flush the dot 3 out. dot3 and dot 5 are not compatible. when I switched over I took the master cylinder, distribution block and wheel cylinders apart and cleaned all the dot 3 off/out of them. I took a couple cans of brake cleaner and flushed all the lines. it's a little work but not difficult.

DOT 3/4 and DOT 5 are not miscible. But they do not react with each other. The glycol and the silicone oil will form two separate layers if mixed. That's all.

You want to get all the glycol out that you can, only because any that is left will gradually attract water and cause corrosion where it sits.
DOT 3 & 4 also have a lower boiling point than 5, so any glycol left in the system will boil first