muriatic acid radiator clean out

   / muriatic acid radiator clean out #1  


Super Member
Dec 16, 2009
gilmer tx
Bobcat CT235
OK, I know y'all (you guys) think I'm touched by now. I admit I do a lot of things that probably don't need done. That is one of the advantages of being retired and a bit retarded. My heat gage on these East Texas 100 degree days has been running up a tad over the midway point on my gage when pulling my finish mower which is my biggest user. I have flushed my system with over the counter flushes but never been happy with the results. I started goggling different home remedies and after quite a bit of reading I determined I was going to try a muriatic acid cleaning. Muriatic acid can be bought at Lowe's for around $8 a gallon. Normal use is for cleaning or etching cement. There muriatic acid is a 20% solution and is actually hydrochloric acid. It is stout stuff and actually reacts with water and causes heating. I removed my radiator, made wooden plugs to mostly plug the inlet and outlet. Cut 3 short pieces of 1/4" hose, plugged one end with a piece of dowel rod, put the other end on the overflow, drain, and small bypass outlets on the radiator. I stood my radiator up. I mixed 2/3 gallon of water and 1/3 gallon of muriatic acid and poured this mixture into the radiator. I let this stay for appx 10 minutes. I then drained and flushed and flushed and flushed. I then mixed up a good dose of baking soda and filled a gallon jug. I poured this into the radiator and let set for 10 minutes or so and again flushed over and over again.

I know this is getting long. During the flush process I did get out a bunch of crud. The jury is still out on my success or failure. I have reinstalled, hooked up my finish mower and let it run in the garage at 540 RPM. Reason I state that is because these high lift blades require a good deal of horsepower even without cutting grass. My thermostat opens at the first mark on my gage, the gage never went any higher than that. I know the test won't be complete until I have tested it on a hot day with a load. Whenever that happens I will be back with an honest report.

I will conclude by saying muriatic acid can be dangerous and I am not recommending this process to the world. Please don't ask what I did with the used acid mix. I disposed of it properly. Might add, the solution can be neutralized with several different products. My radiator may start leaking! Sure hope not. :D
   / muriatic acid radiator clean out #2  
I've used it to take the rust out of a steel motorcycle tank. Did a good job. I used a weaker solution than you did. Great stuff. Battery acid is good for rust too- sulfuric acid.
   / muriatic acid radiator clean out #3  
Radiators are a use I had never thought of. I occasionally use muriatic acid to clean rusty tools and files. It can make an old rusty file look new again and with the rust gone files better.

I'm interested to see your results.
   / muriatic acid radiator clean out #4  
Interesting,I hope it holds up.Keep us posted.
   / muriatic acid radiator clean out #5  
I like this idea and would think about doing it on one of my mowers but- am afraid it might fall apart.......(un) fortunately, that is the only one with any type of restriction in flow.

I've used muriatic acid over the years to deal with hard water caused crud on different items. Caution is an understatement when it comes to the heat reaction in water. I know someone who had the "great" idea of using it to clean their toilet bowl from hard water/rust staining. They dumped in way too much........bubble bubble toil and trouble- crack went the bowl.
   / muriatic acid radiator clean out #6  
I used it to clean up an old encrusted furnace humidifier made from Bakelite (an old thermoset plastic). It looks like new.:thumbsup:

Nasty stuff, though. Wear rubber gloves, a face mask and long sleeves and never pour water directly into acid.
   / muriatic acid radiator clean out #7  
I believe a solution of vinegar would have had the same results although soak time would need to be a little longer...acid is acid.
   / muriatic acid radiator clean out #8  
Pure acetic acid is highly corrosive, more so than hydrochloric acid or sulfuric. Here is an interesting fact: 100% sulfuric acid can be stored in a carbon steel tank but dilute it with water and it will dissolve carbon steel quickly. Weaker solutions are not always less corrosive than pure product. Another acid fact: gold is not affected by nitric acid or hydrochloric acid but mix them together and you have Aqua Regencia and they will readily dissolve gold.
   / muriatic acid radiator clean out #9  
I new I still had some. Used it for YRS. Found it out back. The bucket with the Orange Lid I found it with "Alot" of people will know what for.;) Do you see the label and the Vertical Warning. Not in my Radiator LOL.


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   / muriatic acid radiator clean out #10  
Weaker solutions are not always less corrosive than pure product.

That's true.

Hydrofluoric acid (HF) is called a weak acid, but can dissolve glass. In the semiconductor
biz, we used a mix of HF and nitric acid, called pirana etch cuz it bubbled furiously. It had to be held
in polyethylene containers since it could eat thru pyrex glass.

Aqua Regia (King's water) had to be stored in waxy containers as it was called the "universal solvent".
We did not use that, but it was discovered centuries ago.

I had some good results years ago with copper radiators and HCl soaks. These days with most
rads using aluminum, you have to be less aggressive with the acid.