Should be a reservoir on the firewall driver's side
low brake fluid
try bleeding the brakes or checking the fluid
changing the thermostat in a 1991 geo metro 1.3 liter
Inside car
The 1991 Geo Metro EGR valve can be located on the air cleaner housing. The valve will be on the back of the housing.
Brake fluid does collect moisture. If you've never changed the brake fluid in your system, it probably has moisture in it and yes, it can rust the lines from the inside out.
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If its from 85 then its NOT a geo metro engine. It is probably a Chevrolet Sprint engine because they only started making Geos in 88. If you need an engine for your 95 Geo then you could use one of the following: 1991 - 1995 Geo Metro engine. 1991 - 1995 Suzuki Swift Engine, and 1991 - 1995 Pontiac FireFly engine. Hope this helps :)
4
That depends on what it is doing or not doing.
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You replace it you do not fix it.