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topic 12461

Engine Cleaning with Muriatic Acid

A discussion started in 2002 but continuing through 2018


Q. I am currently rebuilding an engine (1970 Ford 390) and wish to find an acid that will eat the grease and rust off but will not etch the metal. Can a specific strength of muriatic acid accomplish this, and how soon does it need to be rinsed off and painted? Do I need to dip the engine parts or brush them?

Many Thanks,

Mark Byrd
Byrd's Residential Services - Colfax, Washington


A. Hi Mark, just as it's hard to find any single animal which will eat both the carrion & the clover to clean up a field, rust and grease are very different problems so a single chemical to handle both problems probably isn't a great idea. Grease is best removed with solvents or caustics and rust is removed with acid. Get the grease off first, and if you then see a problem with rust, look for a rust remover/convertor. A commercial phosphoric acid based one will be safer for you and your parts than messing with muriatic acid, and it can be dipped or brushed. Good luck!

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. Mark,

To be brief, short and succinct, D O N T !

Any acid will cause problems. HCl, ie. muriatic will attack chrome very nicely let alone ss fastener clamps etcetera. Go and see 6a # 12044 for more advice on using HCl ...

Consider using a proprietary cleaner. Such materials will dissolve oils and are water miscible. Any automotive store should have one! Pour some into an old plastic spray bottle so that you can access hard to reach spots. OK?

Re rust removal, I'm not sure. I really don't know. Personally I would never, ever have contemplated using an acid to remove any engine rust. Maybe HCl or sulphuric with immediate wash-off, drying and then painting. Better still use 0000 steel wool [linked by editor to product info at Rockler].

freeman newton portrait
Freeman Newton
White Rock, British Columbia, Canada

(It is our sad duty to
advise that Freeman passed away
April 21, 2012. R.I.P. old friend).


A. I rebuilt the engine out of my '62 International Scout, it had a bad rust problem on the outside of the crank case, I used a wire cup and a drill to get it all clean, followed that with a nice sandblasting to smooth out the casting marks, finally polished the block to a mild shine, primed with ceramic based primers and painted with ceramic paint. That was 4 years ago and it still looks like factory new.

Just my 2 cents.

John Gardner
- Galt, California, USA

Engine failure

February 21, 2018

Q. I recently got an oil change. 6 days later no oil on my dip stick so I went back to Firestone and complained about it and they put more oil in saying I might have a leak .... but I think they didn't put any in the first time. It's been about a week since they put the new oil in and it's still in there so that means I don't have a leak and it was their mistake right? Could they have messed up my motor?

Shedrick Austin
- Birmingham, Alabama

February 2018

A. Hi Shedrick. This site is about metal finishing than assistance with consumer issues, but sure, it sounds like they forgot to put enough oil in. My guess, but I'm no mechanic, is that if you hear no funny noises your engine is going to be okay.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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