Thread: Electrolytic rust removal for engine block

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Thanks, I will make sure it's dunked well under the water. I have a vice grip that is helping hold the head in the correct place in the bucket, and you can definitely see a line on that when it comes out of the water.I was thinking about coating all the machine services with a moly grease or something, it seems like this process has no effect on Grease. I checked on it this morning, it was unbelievable how nasty the water looked on the top. I looked inside the water jacket, it is getting better but I'm going to it sit until I'm happy with it.

Well, here it is after about 4 days in the tank, it is making a difference, but I can't say it's a day and night difference but it is better. I'm also glad I started with the head, clean up of the slime and black residue it leaves behind will be too much for a machined block. I might try Mikes citic acid soak and pound in some new cam bushings if need be.

Yep, it is a nasty process! Especially with iron anodes. That's why I switched to carbon. The slime pretty much goes away with carbon.

It does look to me like it was getting there and your results look like mine (just not on an engine), but it might have taken another week to really get it clean.

Originally Posted by Hotrod46

Yep, it is a nasty process! Especially with iron anodes. That's why I switched to carbon. The slime pretty much goes away with carbon.

It does look to me like it was getting there and your results look like mine (just not on an engine), but it might have taken another week to really get it clean.

Oh, the carbon doesn't leave the mess either? Maybe I'll have to try that first. I got to start on the kitchen soon for a big honey do list so it can sit for months

Seth, I have a source for large carbon brushes out of commercial generators. These are not pure carbon and I have trouble with them breaking down and literally melting after being in the electrolyte for a few days, but they are a soft carbon (maybe even some kind of composite). It doesn't matter because I have a bunch of them. It's my understanding that hard carbon anodes don't break down much and will last a long time. This will allow the process to go on for days or weeks with not much attention, other than topping off the electrolyte.

The black residue is the pure iron that was locked up in the rust. Rust is one iron atom combined with two oxygen atoms (FE02). The iron is left after the oxygen is liberated in the electrolysis. It will always be left.

Seth I seem to recall that your major concern was the rust that was mostly in the bottom of the water jackets.

If I was doing it what I might try would be to put in some freeze plugs (maybe the rubber kind just snuged enough to make it water tight and throw a water pump or block off plates to cover those holes and then fill the block with the citric acid and water solution.

If you have the block sitting flat like the photo in post 1 the citric acid shouldn't get on any of the machine surfaces , even if you have to pull the freeze plugs a time or 2 to change the solution.


The citric acid will work in cold weather, but it takes a bit longer when it's cold. Seems like I soaked the HEMI block for a bit over a week when I did it in December last year.


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I was looking at it today and I think I'm going to bolt on what I can to block things off ,use some gorilla tape for the rest and take my siphon feed bead blaster to remove the worst. Then I think I'll pop in some new frost plugs and fill it with citric acid and change it out now and then like you said. I could even set it on end with the head bolted on and fill it through the water pump hole.