When new the cars used DOT3 as DOT4 was not available yet. DOT4 is an
improved DOT3. DOT5 is a silicon brake fluid that is not hygroscopic
like DOT3/4, however is can not be mixed with DOT3/4 and once a system
has been filled with DOT3/4 it is not wise to refill the system with
DOT5 even after it has been rinsed thoroughly. Only if all rubber
components have been renewed you can use DOT5 safely.
There is another brake fluid DOT5.1 which can be regarded as an improved
version of DOT4. This does mix with DOT3/4 but not with DOT5.
Use DOT4, any make will do, widely available, cheap and safe. It will
absorb water so you have to change the fluid every 2-3 years, depending
on the climate. Because of this you will automatically clean out the
system periodically
DOT5 hardly absorbs any water, which, if entered, then will collect in
some low spot in the system and cause corrosion unnoticed. Most people
think that you do not have to change it periodically because the is no
water absorption, however there is still wear in the system. It is also
slightly compressible giving a very slightly spongy feeling. These are
the reasons I do not like to use it.
A can of worms has been opened again.
Kees Oudesluijs
NL
Op 12-10-2013 4:32, Greg Lemon schreef:
> People have mentioned DOT 3, 4, and 5, but I don't think anybody had
> really given much background.
>
> When new the cars used DOT 4 fluid, usually if not always Castrol or
> Girling brand. DOT 3, the stuff you can pick up at the local
> convenience store or wherever, was not recommended.
>
> I believe if you have a totally rebuilt system with new rubber
> components you can now use DOT 3 , willing to be corrected if that is
> not the case.
>
> Dot 5 can be used as well, but does not mix with DOT 3 or 4, as
> mentioned, DOT 3 and 4 mix ok. Most people only use DOT 5 after a
> complete rebuild of the system or at least a thorough flush.
>
> So the question is, has your system been rebuilt and what it it
> running now?, most DOT 5 I have seen is purple versus a golden color
> for most DOT 3 and 4s, but in an old system with old fluid they will
> all often all look kind of brownish grey.
>
> If you don't know what is in the car you might take a bit out of the
> reservoir and mix it with some DOT 3 and see if it mixes if it is DOT
> 5 will be like oil and water, if not you probably have DOT 4 or three.
>
> So bottom line is most likely it has DOT 4, as the was OEM, but many
> run DOT 5 these days and some probably DOT 3 too, since these cars
> have been around for so long hard to know for sure without some
> testing unless you have a reliable history.
>
> Greg Lemon
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--
Kees Oudesluijs
Dorpsstraat 183
2995XG Heerjansdam
T: 078-677 1233
E: coudesluijs@chello.nl
Technische commissie Jensen Healey en GT
Het Jensen Genootschap Holland
www.jensenholland.nl
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