What type of brake fluid should I use after a brake line replacement?

Your opinion?

What type was used originally?

Thanks to all for their input - DOT 4 will be my choice.

After reading some search results, I am a bit surprised that silicone was not suggested - I guess that the age of the system is a big factor.

Now, I have a bit of work ahead of me!

Basically silicone (DOT5) brake fluid is not recommended for a couple of reasons. First, it's not hygroscopic (does not absorb water0, so any water that gets in there through condensation, etc, will roll around, causing corrosion. Second, it foams easily, causing a soft pedal. There's more you can google.
--
1992 745, >500k km (now gone, but not forgotten)

DOT 4
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

Agree with DOT 4 or DOT 3 if 4 is not available.

I would not recommend DOT 5 in a plain old vintage Volvo.
Made that mistake in my 220.

DOT 3 brake fluid only in an emergency and then a flush with DOT 4 ASAP.

DOT 3 is a lower grade of brake fluid and can damage some of the internal rubber seals.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

I thought DOT 3 and 4 were compatible, with boiling point being the difference. DOT 4 with a higher boiling point. Could you elaborate?

There are two high performance Japanese built cars (GS400) in the family. The owner's manual specs just DOT 3 brake fluid.
--
john

They are compatible, but due to manufacturers recommended specifications, replacing DOT 4 with DOT 3 is NOT recommended. Besides, I might be liable if for some reason a judge decides that DOT 3 used in a system that called for DOT 4 caused an accident and I would like to stay in business a little while longer.

I have to admit that we only use DOT 4 and stock nothing else because of tradition and because Volvo has always called for it. And it is legally accepted to top off or replace DOT 3 with DOT 4.

From personal experience over 20 years ago, a customer bought a full set of wheel cylinders and installed them himself in his Volvo 544 and within a year, the wheel cylinders were leaking. He had used DOT 3 instead of DOT 4 and when we got to check out it out, we found the edges of most of the seals in the wheel cylinders were worn down. The bores were in excellent condition so we replaced all the wheel cylinder seals and flushed with DOT 4 and problem solved.

I can't swear the DOT 3 caused the damage, but I prefer to err on the side of safety. A lot of British vintage car enthusiasts swear that DOT 3 can damage the natural rubber used to make early brakes seals, but I have never seen any documentation to support that, but brakes being so important why mess around.

And I don't like upgrading to silicone fluids either.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

While we're on the subject of brake fluids, should we use DOT 4 in the clutch cylinders also??

Volvo recommended DOT 4 for the clutch hydraulics too and is what we use.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

I've been following this thread and since there was mention of British cars thought I'd add this. My first cars (1965) were British from the 50's. They required a red hydraulic fluid made by (IIRC) Girlng. The fluid available in the US at the time would kill the seals. - Dave

Either is fine - the main difference is DOT 4 is a bit less hygroscopic and therefore has a slightly higher boiling point. There’s nothing magical about Dot 4 - my 2017 Mazda is spec’d to use DOT 3.
--
82 242-6.2L; '17 Mazda3; '16 Crosstrek

The red hydraulic fluid you mention was probably similar to Mil. spec. 5606 which is commonly found in aircraft hydraulic systems. They use it as "brake fluid" also. I actually think it's very similar to the red ATF and have often thought about using ATF in the clutch, but haven't yet. Maybe someone else out there has tried it and will post their results/opinions here.

No, ATF will rot the seals in a brake system.