Rust removal in engine: oxalic acid

[Spinneyhill]

I want to use oxalic acid to chelate the rust in the block and head. I have read of a dose of 1 kg for 12 L; my system is c. 12.9 L so I will use 1 kg of oxalic acid powder in the water.

 

How long should it be in there? I suspect a couple of weeks with frequent running?

 

There is reference on these fora to citric acid in the same dose, but it is not given how long to leave it in.

[Rusty_OToole]

That sounds like a hell of a dose. Leave that in there a couple of weeks and there may not be much left of your engine. I would try a much smaller dose, say 1/10 or less, and leave it in for an hour and see what happens. If your cooling system is bad you will probably find the water saturated with muck. Drain it off and try again with fresh solution. It may take 3 or 4 treatments to get it decently clean. Flush with fresh water a few times or neutralize with some kind of base.

 

I would more likely use a flushing compound made for cars or else CLR. I know people that have used it with success and it is less likely to eat hell out of your water pump, seals and gaskets.

[Owen_Dyneto]

I pretty much agree with Rusty, that sounds like a massive overdose.  I've used oxalic acid many times over the years for cleaning cooling systems.  I used about 1-2 cups for a 20 quart cooling system, and predissolve it in warm water first.  Then I go for a drive, maybe an hour or so, and then drain, flush; and fill again using a neutralizer like sodium bicarbonate, and flush yet again before returning to whatever my normal coolant was.

Edited March 3, 2018 by Owen_Dyneto (see edit history)

[edinmass]

Chelate.......to remove rust by removing the oxygen from the scale in the head/engine will not effect the metal. I use evapo rust, expensive but safe. I think you can get it at harbor freight. After cleaning the head and block to the best of you ability with it, I would then reassemble the engine, and put three gallons of it in the engine and top off with water , then run the car for a month. I have done this in the past, and heating the mixture makes a big difference in its effectiveness. Also, and scale in the radiator will dissolve. I had a Pierce that pushed water even after cleaning the head and block, I ran the mixture for sixty days, presto, no more water pushing out the over flow. Upon disassembly for a different reason, the block looked like it just came out of the foundry. Perfectly clean, no damage. Heat to the processs is the key, it speeds up the reaction time. Often, if I have a head or block that has severe rust issues, I will use a very aggressive acit for a very short period of time, then switch over to the evapo rust. Works like a charm. Ed 

[auburnseeker]

You can get evaporust from Amazon as well.  I think that was the last place I found the best deal on it.  

[DavidAU]

I've used Evaporust also.   I have filled up two side valve Ford V8 engines which both had red rusty water in them and let them sit for three days before draining and flushing them. 

Both engines came out very clean and are now in use with no sign of rusty water.

    

You can also re-use the Evapo Rust liquid quite a few times before it looses its effectiveness.

 

[Rusty_OToole]

5 minutes ago, DavidAU said:

I've used Evaporust also.   I have filled up two side valve Ford V8 engines which both had red rusty water in them and let them sit for three days before draining and flushing them. 

Both engines came out very clean and are now in use with no sign of rusty water.

    

You can also re-use the Evapo Rust liquid quite a few times before it looses its effectiveness.

If this is true you could leave it in a 5 gallon pail for a couple of weeks and all the solids would settle to the bottom leaving clear liquid,

5 minutes ago, DavidAU said:

 

 

[edinmass]

 I have been wanting to try citric acid instead of Evapo Rust for quite a while.  You can purchase it from wine making supply houses for very little money.  Chemically should work just like Evapo Rust.  You should be able to make it for about 40 cents a gallon.  I will try on my next find barn find car. 

[Spinneyhill]

Thank you for your replies.

 

I am in New Zealand and I would need a mortgage to buy enough Evapo-rust.

 

I found a forum where citric acid and oxalic acid were compared. One of the correspondents was a chemist said the oxalic was more effective because of its structure. That is where I got the dose from. These mixtures are said to not attack paint.

 

I made up a half strength mixture. I have the thermostat out for replacement so I put the head outlet connection in the mixture. After 24 hours it is cleaner but still covered in nodules. The paint seems intact but we'll see when I remove it later today.

 

I got the oxalic acid in 500 g screw top plastic "jars" from the hard ware store paint section. Mainly used as a cleaner, apparently.

Edited March 4, 2018 by Spinneyhill (see edit history)

[Spinneyhill]

Here is the post about its structure, from https://www.bikeforums.net/classic-vintage/596846-oxalic-acid-better-than-citric-acid-rust-removal.html

 

"Road Runner's" post at https://www.jalopyjournal.com/forum/threads/best-way-to-de-rust-cooling-system.943881/

is also very good.

[Larry Schramm]

7 hours ago, Spinneyhill said:

Thank you for your replies.

 

I am in New Zealand and I would need a mortgage to buy enough Evapo-rust.

 

I found a forum where citric acid and oxalic acid were compared. One of the correspondents was a chemist said the oxalic was more effective because of its structure. That is where I got the dose from. These mixtures are said to not attack paint.

 

I made up a half strength mixture. I have the thermostat out for replacement so I put the head outlet connection in the mixture. After 24 hours it is cleaner but still covered in nodules. The paint seems intact but we'll see when I remove it later today.

 

I got the oxalic acid in 500 g screw top plastic "jars" from the hard ware store paint section. Mainly used as a cleaner, apparently.

 

In the 80's when I was a rep for GM, We used oxalic acid to remove rail road dust off the paint of new cars. No problems if washed well after the treatment.

[EmTee]

On 3/4/2018 at 1:46 PM, Spinneyhill said:

I got the oxalic acid in 500 g screw top plastic "jars" from the hard ware store paint section. Mainly used as a cleaner, apparently.

 

Yes, the last time I bought some I found it on Amazon, listed as "wood bleach".

[Mark Shaw]

1 hour ago, EmTee said:

Yes, the last time I bought some I found it on Amazon, listed as "wood bleach".

 

I used it on my walnut steering wheel to remove black stains.  It worked great!  Just remember to neutralize it after it does it's job.

[Spinneyhill]

The head outlet connection was in the half strength mix (500 g in ca 10 L of water) for four days. The paint was still pretty good after 3 days but was starting to bubble in places after 4. It was at room temperature. Much rust came out of it. Here it is after 3 days. The bucket is the debris that came out after three days.

   

I am disappointed I allowed you esteemed gentlemen to talk me out of the full strength mixture. However, I put the half strength mix in the engine and ran it up to temperature for about 20 minutes. I ran it again similarly after 4 days. After 8 days I drained the coolant (oxalic acid mix). This is what it looked like.

    The deep green colour is the chelated iron oxide in solution in the fluid.

This is the first flush and the stocking bag from the inlet hose. You can see through the water a little. I'll come back with the contents of the bag when the wash water has settled.

 

Still to do are a second flush then a sodium bicarbonate flush than refill with coolant.

[Rusty_OToole]

I would rather go easy and do 2 or 3 treatments but you can go as you please. Thanks for reporting your results. Let us know how the full strength mixture works.