Ok to use DOT4 instead of DOT3?

Associate
Joined
28 Feb 2007
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1,479
MX5 (MK1)........

My clutch is biting right at the bottom of travel, the fluid reservoir is empty......

Im pretty sure the slave cylinder is leaking, no problem, its a £14 part on MX5parts :D

Wont be able to fit it untill the weekend after next though, so I need to top up the fluid before I run out completely, I have a bottle of DOT4 but the filler cap specifies DOT3, ok to use or a bad idea?

My google skills fail me tonight as I cant find anything conclusive apart from that they are very similar.

EDIT: on the bottle it says it meets the specs of dot 3 and dot 4, im just worried about it corroding plastics etc
 
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Associate
Joined
28 Feb 2007
Posts
1,479
DOT3 hasn't really been used for ages, probably got DOT4 in anyway. I'd just top it up tbh

I figured this as they do not sell it in halfords, Im going to ring round some places tomorrow to see if I can find someone who sells DOT3.

If not, then DOT4 goes in and I will flush the system with it or something when I change the slave cylinder :o
 
Soldato
Joined
23 Nov 2007
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2,994
Location
Midlands
Brake fluid should be changed every 2 years anyway, so get it done along with your hydraulic clutch if you have one. You can drain the old stuff and put DOT4 in no problems
 
Soldato
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18 Oct 2002
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16,659
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Devon
IIRC Federal regulations require a basic level of compatibility between DOT3 and DOT4. The crappy silicon DOT5 fluid is the one to be wary of which should never be mixed. If you are concerned then check the wording on the bottle, the majority of manufacturers will say it's safe to mix with other mineral fluids.

I would hesitate to put DOT3 in a braking system that the manufacturer has specified DOT4 fluid for, but as others have mentioned the clutch is far less critical in this respect.
 
Associate
Joined
12 Feb 2009
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514
Dot3 was being replaced when I worked in the spares trade 15 years ago. I'd top up with Dot4 and then obviuosly use Dot4 when you change the cylinder.
 
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