Hi everyone, thanks to all for the input on my question regarding
using phosphoric acid to clean my mk2 cooling system of rust.
I would like to make a few comments: All acids are not the same, I
might use phosphoric acid (diluted to about 0.1 molar) because it reacts
fairly slowly with iron/steel and will reduce rust to iron phoshate
(which can be flushed out subsequent to treatment). It also leaves a
thin layer of iron phosphate on the surface of the metal which somewhat
inhibits further rusting. Naval jelly is gelled, dilute phosphoric acid
and is commonly used for rust removal, for example.
Muriatic acid is a concentrated solution of HCl (a gas) in water
and is very dangerous! While it will disolve rust (as will most acids)
it will also attack the metal at a greater rate at use dilution than
phosphoric acid. Not only that, but unless thoroughly removed,
hydrochloric acid will promote rust at a very rapid rate. For a short
synopsis, check this url:
http://www.geocities.com/MotorCity/Downs/3837/deruster.html
So, I might use diluted phosphoric acid for rust removal in my
cooling system (or other areas) but would never suggest using hydrochloric
acid (muriatic acid)! Certainly, no one should use undiluted muriatic
acid for anything unless you are very familiar with its properties.
I did a compression test today. 100 to 110 psi. Is this low for a
ll47 engine? It was warmed up, but I forgot to open the throttle.
thanks, David
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