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Old 05-15-2015, 04:33 PM
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Mermaidquest Mermaidquest is offline
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Engine flush with phosphoric acid?

I am under the impression that muriatic acid is for calcium/lime dissolving as used in the swimming pool industry. I would think that phosphoric acid would be the a better choice.I have found the overpriced green stuff sold under the marine price for a mere 7 dollars a quart at Loews building supply under the name of rust primer in the paint section. I took the plunge and dumped a pint into the thermostat chamber prior to reinstalling the thermostat.I bolted shut the housing,started her up let it run for about 3to5 minutes. Then shut it down installed the thermostat and and it runs at the coolest ever! I did also install a ball valve restrictor in the "loop".It performs perfect at half open. Prior to this I boiled alot of water all around Florida. Any thoughts on chemical reactions?
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Old 05-15-2015, 09:31 PM
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marthur marthur is offline
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What precipitates out of seawater in the engine is mostly calcium carbonate ("lime"). Salt is very easy to dissolve, so that isn't the biggest part of the blockage.

Any decent acid will react with the calcium carbonate. I tested some that I scraped out of a project motor and found that Vinegar also does the job, just takes longer than the concentrated acid.

The phosphoric acid is used in rust converters to convert rust to a layer of iron phosphate.

Last edited by marthur; 05-15-2015 at 09:37 PM.
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Old 05-16-2015, 07:34 AM
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BunnyPlanet169 BunnyPlanet169 is offline
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Muriatic is commonly used by the steel industry to remove flash rust from coils and sheet stock. It's dilute hydrocloric acid IIRC. I suspect phosphoric is more commonly sold for 'do it yourself' because it's not such a nightmare to play with.

S/V Bunny Planet
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Old 05-16-2015, 01:20 PM
toddster toddster is offline
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Well, hydrochloric acid (swimming-pool strength "muriatic" acid is actually a fairly concentrated form) will solubilize scale and rust. Phosphoric will also, but residual phosphate, combined with engine heat, will react with calcium and iron to form insoluble crystals. Apatite, vivianite, stuff like that.
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Old 06-13-2015, 11:00 PM
BobinSF BobinSF is offline
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For future flushing, I bought 'Trac Descaler Barnacle Buster' from West Marine. The MSDS says it is phosphoric acid. The ad copy speaks of it being effective at removing all sorts of things. The ad copy says it is non-toxic and biodegradable, but only talks of recirculating it and then pouring it down the drain, but not running it through the wet muffler and out into the seawater. I haven't tried it yet.
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