Which DOT
Le Mans Master
Joined: Aug 2017
Posts: 6,928
Likes: 1,486
From: New Jersey
Dot 3 or 4... dot 4 has a higher boiling point. Dot 5 is silicone... you could use Dot 5.1 which is compatible with 3/4. I'd use Dot 4 as it's available pretty much everywhere and inexpensive.
Pro
Joined: Jan 2022
Posts: 688
Likes: 243
From: Spokane Wa.
In a clutch application I think 3 would be fine as not much need for higher boiling point there. Also, 3 is less likely to absorb moisture than 4 from what I have read. If you are thinking of a brake flush also than it would be best to do both with the same and have less chance of a half empty bottle sitting around absorbing moisture.
Instructor
Joined: Jul 2020
Posts: 226
Likes: 43
From: New Jersey
When we replaced the hydraulics on my son's, we went with one by Valvoline labeled as "Synthetic DOT 3 & 4." I had read somewhere that it's what Bill Boudreaux recommended. It's seemed to work alright for us, though we're admittedly not using the car in a very demanding way where we'd have to worry about burning/boiling the hydraulic fluid.
Racer
Joined: Mar 2020
Posts: 384
Likes: 144
From: Langton, Ontario, Canada
2025 C4 of the Year Finalist - Unmodified
In my 85 4+3, I put Dot 5 silicone brake fluid in the clutch system. It doesn't attract moisture, so it's good for a long time. The 85 doesn't have ABS, so I put it in my brake system as well. DOT 5 Silicone foams with ABS brakes.
