DOT 3 vs. DOT 4

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grinder - 26 Aug 2005 19:54 GMT

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?

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z - 26 Aug 2005 20:09 GMT

> 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?

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.'

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J Strickland - 26 Aug 2005 20:16 GMT

DOT4 isn't difficult to find. Go to another store.

> 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?

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Bob - 27 Aug 2005 15:52 GMT

> 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?

In my old E28 I discovered that DOT3 caused the rubber to deteriorate.
I switched to DOT4 and the problem was solved.

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fbloogyudsr - 27 Aug 2005 16:29 GMT

>> 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
[quoted text clipped - 4 lines]
> In my old E28 I discovered that DOT3 caused the rubber to deteriorate. I
> switched to DOT4 and the problem was solved.

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fbloogyudsr - 27 Aug 2005 16:32 GMT

Sorry about the earlier empty message - finger twitch.

> grinder wrote:
>> After changing the oil in my 318ti I was going to top off the fluids.
[quoted text clipped - 5 lines]
> In my old E28 I discovered that DOT3 caused the rubber to deteriorate. I
> switched to DOT4 and the problem was solved.

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

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MWarren - 27 Aug 2005 22:42 GMT

> Sorry about the earlier empty message - finger twitch.
>
[quoted text clipped - 13 lines]
>
> Floyd

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

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