Brake fluid. DOT 5 versus DOT 3 or 4 ...Paint safe?

[Kern Dog]

I decided to switch to DOT 5 brake fluid in my car since I was replacing the front brakes and master cylinder. I wanted the DOT 5 for the simple reason that it isn't harmful to the paint. I've had leaks eat the paint on the fender aprons and frame rail. I wanted to avoid that from now on.
I noticed that DOT 3 and DOT 4 is now available in a silicone formula.
Does this mean that the 3 and 4 are also paint friendly?
The DOT 5 was over $35 a quart. I know prices have risen on everything but jeez...If the 3 or 4 silicone stuff is safe, it is about half the price!

 

[PlymCrazy]

 

[khryslerkid]

Haven't heard of that one before.

I'm using dot 5 for the same reason, getting 3 or 4 on paint. Dot 5 will have the slightest bit of sponginess to it.

A good flushing will be required to rid the system of the old fluid first. There's a thread on here somewhere on what's best to use.

 

[khryslerkid]

If the 3 and 4 silicone has glycol-ether in it, it could still eat paint. 3, 4, and 5.1 have glycol-ether in them. Dot 5 is a silicone with no glycol-ether.

What I've read is the standard 3 and 4 can be mixed with the silicone 3 or 4 but definitely not with Dot 5.

 

[Kern Dog]

Haven't heard of that one before.

I'm using dot 5 for the same reason, getting 3 or 4 on paint. Dot 5 will have the slightest bit of sponginess to it.

A good flushing will be required to rid the system of the old fluid first. There's a thread on here somewhere on what's best to use.

The front calipers are new. The master cylinder and hard lines to the front are new. I have already bled the brakes and pushed out most of the old DOT 3 fluid.
I'm not a broke dick, I just don't like to spend money where it can be saved. If a DOT 4 silicone can be used and still have the same qualities, I'm all for using it. I'm not towing anything, I'm not racing it on road courses every week either. I doubt that I'd reach the limits that DOT 5 have in terms of temperature.

 

[khryslerkid]

The front calipers are new. The master cylinder and hard lines to the front are new. I have already bled the brakes and pushed out most of the old DOT 3 fluid.
I'm not a broke dick, I just don't like to spend money where it can be saved. If a DOT 4 silicone can be used and still have the same qualities, I'm all for using it. I'm not towing anything, I'm not racing it on road courses every week either. I doubt that I'd reach the limits that DOT 5 have in terms of temperature.

Dot 4 synthetic still has polyethylene glycol ethers which I'm sure it's what will eat paint. Here's a good breakdown...

Synthetic Brake Fluid Dot 3 & 4

 

[mrmolding]

After reading all of the reasons not to use DOT 5, I really wanted to see if there was another option to DOT 3. I had DOT 3 destroy some areas of paint after a battery cable started touching the master cylinder lines while I was driving. The cable touched both lines and sparks started flying out of the front of the car. The previous owner put in a reversed terminal battery and the cable just reached the terminal with an aftermarket cable. Oh well. It had been a while since I'd stared at a Mopar and I missed it. It cut one of the master cylinder lines in half and poured DOT 3 all over my engine bay and it went all over the paint. I had to have the car towed since I was miles from a new cable. I wiped most of it off in time, but a few areas made it to the metal.

Anyway...when I replaced all lines, wheel cylinders, master cylinder, etc on my next car -- 70 RR, I found one of Rick Ehrenberg's articles about the joys of DOT 5. I've bought a fair amount of parts from him so I asked him how he felt 20 years after he wrote the article and he said ignore the noise and try DOT 5. So, I did. I agree that it is a tad spongy at first but I've seemed to get rid of it with a second bleeding and re-adjusting of the brakes.

I've had it in for almost two years and I think the brakes are better than on my daily driver. So a few extra bucks for DOT5 is insurance, but who knows in the future if the other fluids will have a new formula and be more affordable.

 

[dadsbee]

Zero issues with DOT 5 in my Bee. Brake pedal is no different than any of the other cars with DOT 3 in them.

 

[Don Frelier]

I've had the same master cylinder in my charger since around 2000. No issues.
I change any car I own to dot5 almost immediately and I haven't had to replace calipers either which is a common problem with cars driven year round here.

 

[Kern Dog]

I looked in the cabinet and found this:

I didn’t know the stuff I bought for the other cars had a silicone formula.
The DOT 5 stuff I bought didn’t clearly define it on the front.

It did on the back though.

 

[ruffcut]

I've got Dot 5 in both my cars with no problems! ruffcut

 

[Dan64]

Just make sure to really flush a ton of Dot 5 thru the lines and rear calipers . When Dot 3 & 4 come into contact with Dot 5 it can jell causing poor brake performance. Other than that i'm a big fan of not destroying my paint job.

 

[dvw]

Been using Dot 5 for 30+ years. Street cars, drag cars. Never an issue. And all the paint is still nice.
Doug

 

[mrmolding]

So I got curious and looked up the ingredients in the synthetic O’Reilly DOT 3 and it says:

• Fluid Composition: Diethylene Glycol

Searching on Diethylene Glycol is an alcohol based solvent. I’m not a chemist but I think the alcohol is what dries up water in brake lines using DOT 3 so I guess even if it says synthetic DOT 3 it still has alcohol that can remove paint.

 

[Boris7K]

Kern Dog asking all the right questions! Thanks, I'll be using DOT 5 this time around.

 

[YY1]

I replaced the same parts you did, but I also replaced the rear wheel cylinders.

I flushed the valve and front to rear line thoroughly with brake-kleen.

My master cylinder is still black (not rusted) after 8 years.

 

[copper67sat]

I put DOT 5 in my Satellite when I restored it 30 yrs ago and haven't had any problems with it. Everything was off the car so flushing the lines was easy. I remember being told at the time to replace any rubber in the system as it would have absorbed some of the old DOT 3 fluid, but I was replacing the rear wheel cylinders and rebuilding the front calipers anyway so that took are of it.

 

[Derwud]

I run Dot 5.1 has not eaten paint and pedal is FIRM.. Still use Dot 3/4 for Clutch.

 

[Master Gunner]

The military's been using DOT 5 for years, of course they're not really concerned about paint damage. Main reason to use 5 is that it is not hygroscopic (does not absorb water)

Mark

 

[Dennis H]

Sprits a little of the 5 on the fender and report back.