Electrolytic rust removal for engine block

I got my 218 back from the engine shop and they soaked it in what ever they use to clean up the rust. It is nasty enough that he said I will need new cam bushings afterwards. It still has a heavy build up in the bottom of the water jackets, enough for a hammer and screwdriver and I would like it out of there. I would like to use electrolytic to try to remove it but does it work well with hard rust built up that heavy? All the machine work has been done to the block that shouldn't be an issue should it? I know hindsight it is 20/20.

I've used electrolytic to derust some tools and lathe parts. I didn't seem to have any effect on unrusted surfaces, but I didn't measure anything either.

From what I have read, it only converts the rust at the molecular level by liberating the oxygen from the FE02 and doesn't hurt good surfaces. All that's left is basically the pure iron that was converted to rust in the first place. It gets left behind as an ultra fine black powder. This needs to be rinsed off pretty quick, since it sticks pretty good after it dries.

I think you will be OK with the machined surfaces, but they may discolor some. The lathe chuck I did was really bad. So bad that it was almost completely stuck. All four jaws were like that. After about 3 days, I was able to get it disassembled easily, but it took several more days to get it completely clean. There were many fine pits on it, but that is because it was literally covered with rust. If the metal has been eaten away by rust, it will still be eaten away and there will be a pit, just no rust.

Also, the process is similar to chrome plating. It works better on "line of sight" to the anode, but it will work in hidden places. It just takes a lot longer. I read about a guy that had an old antique post drill that had been through a fire and looked completely hopeless. He hooked it up and left to go on a cruise (as on a ship) for several days. When he got back, he was able to get every bolt out with no issues. Almost seems like magic! It did work wonders on my old chuck, which also looked pretty hopeless.

FWIW - I found that using carbon for the anode works much better than iron. The iron anode will get a scummy covering of very nasty looking rust and the rust removal process slows down if it's not cleaned or replaced. Carbon doesn't do this, but will darken the water, leaving it black. Don't use stainless for the anode. This will release Hexavalent chromium into the solution. That's pretty nasty stuff.

Good luck.

What do you mean by " line of sight " is that the things like inside the water jackets? It can stay in for a month for all I care, I'm not in a hurry. Now I need to find where to buy a carbon stick.

The outside of the block would be in a direct line to the anode(s), so would be line of sight. Unless you can get an anode inside the water passages, then the current would have to take an indirect path. That would not be line of sight. The current would still flow through the electrolyte, but it would have to travel a longer path with more resistance.

When I was doing the lathe chuck, the center hole was taking a long time to clean up. I suspended an additional anode in the center of the hole and it cleaned right up. I'm not saying it won't work in indirect locations, it will just take longer.

Thanks, I bet I can slip something through the water jackets.

You know, after thinking about it, you would not even have to submerge the entire block if all you want to do is clean the inside. If you can get an anode or 3 inside the water passages, just seal the block and fill it with electrolyte. That way it will not be able to affect the machined surfaces. Just leave the top open so you can let the gas escape (oxygen and hydrogen) and to add more electrolyte as needed. Obviously, you can't let the anode touch the block.

That's a great idea.

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Originally Posted by Hotrod46

You know, after thinking about it, you would not even have to submerge the entire block if all you want to do is clean the inside. If you can get an anode or 3 inside the water passages, just seal the block and fill it with electrolyte. That way it will not be able to affect the machined surfaces. Just leave the top open so you can let the gas escape (oxygen and hydrogen) and to add more electrolyte as needed. Obviously, you can't let the anode touch the block.

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I did some checking on that idea, it would be quite a bit of messing around. It would work well otherwise though.

I got my dunk tank made. I gathered up some fencing push posts I had that are made of re bar and welded them up for the + side of things. Does it look like something that will work ?

It'll work - how heavy is the metal? You'll want to lift it out and clean the rods as they'll become covered in "gunk".. no problem other than that from what I can see.

It's 3/8 rebar ,I can easily lift it out. I'm going to place the barrel right under my chain hoist so I can lift the block in and out and inspect it. Maybe I will start with the cylinder head, if something weird happens I got three more backups LOL.

I'll be interested to see how it works out especially on the machine surfaces.

I was happy with the results of the citric acid on the Hemi block I did last year, but that was all pre-machine work........It would have had to have the machine work re-done afterword if it had already been done and cam bearing would have been junk.


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I started the electrolytic process on the head, I have a before shot of the rust on the radiator hose outlet. I have the charger running on about 2 amps and I could see some bubbling in just 15 minutes. After one hour there was very noticable stuff going on. I'm anxious to see what it looks like in 24 hours.

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Originally Posted by Mike P

I'll be interested to see how it works out especially on the machine surfaces.

I was happy with the results of the citric acid on the Hemi block I did last year, but that was all pre-machine work........It would have had to have the machine work re-done afterword if it had already been done and cam bearing would have been junk.


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I wonder if that is similar to the stuff the machine shop uses.

Seth, just another thought on the machined surfaces. I have noticed that if a section of the part gets above the surface of the electrolyte, there is a definite line created on the part where it comes out of the water. Not sure if there is any metal removed or if it's just discolored metal. Be careful to keep it submerged since the process not only converts rust, but also breaks the water down into gas. The level will drop over time.

Like the others, I'm very interested in how this turns out.

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.

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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.

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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.