DOT 3 vs. DOT 4

After changing the oil in my 318ti I was going to top off the fluids. The brake fluid reservoir says only use DOT 4 brake fluid. The supply store
only has DOT 3.
Anybody know the difference or if DOT 3 can be used?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I had always thought you could put dot 4 into a dot 3 system but not the other way around, however according to this: http://www.xs11.com/tips/maintenance/maint1.shtml
'DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. In an emergency, it'll do. Silicone fluid will not mix, but will float on top. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures, which is why the US Army likes silicone fluids. Since few of us ride at temperatures very much below freezing, let alone at 40 below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances.'
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
DOT4 isn't difficult to find. Go to another store.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
grinder wrote:

In my old E28 I discovered that DOT3 caused the rubber to deteriorate. I switched to DOT4 and the problem was solved.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sorry about the earlier empty message - finger twitch.

That's not quite a crock. Dot 3 is Castor Oil - brake fluid has always been an organic oil to *PREVENT* the rubber brake lines from breaking down. You probably had aged lines or contamination.
Floyd
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote

If this is the case why does it disfigure (deteriorate) plastic grills and destroy paints? Is it the petroleum base in the plastic that it doesn't get along with?
Matt
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.