Rust removal in the water jackets

Merc Cruzer

Merc Cruzer

Well-known member
I have a 53' Merc Flathead block that has been dipped and magnafluxed - no cracks. I have been doing the long screwdriver and brushes in the water jackets, but want the water jackets cleaner. I am going to bolt the heads back on the block with old head gaskets, stand it up and then fill the water jackets, let it stand and the flush them out. From the past posts, the options are:

Phosphoric Prep and Etch from the Home Depot
Evapo-rust
Molasses (which by the way I cannot find locally)
Oxalic acid crystals (aka. Wood bleach in hardware stores)
Vinegar

....thoughts on which one would be the best for this project.
 
Merc Cruzer said:
I have a 53' Merc Flathead block that has been dipped and magnafluxed - no cracks. I have been doing the long screwdriver and brushes in the water jackets, but want the water jackets cleaner. I am going to bolt the heads back on the block with old head gaskets, stand it up and then fill the water jackets, let it stand and the flush them out. From the past posts, the options are:

2. Phosphoric Prep and Etch from the Home Depot
Evapo-rust --not sure, but I wonder if the main ingredient is phosphoric acid??
Molasses (which by the way I cannot find locally)
1. Oxalic acid crystals (aka. Wood bleach in hardware stores)
3. Vinegar

....thoughts on which one would be the best for this project.
Click to expand...

My .04 (inflation)
 
Phosphoric is the better acid of the bunch in relation to iron. It will convert iron oxides to iron phosphates that are less likely to get a major reoccurence of iron oxide unless you run it with no anti-freeze or water soluable oil when back in service. It will eventually corrode again but it will take more time than bare cast iron for sure. Oxpho is what I use in a dilluted form.

Yep it's Ospho. Was typing too fast for my brain.
 
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I think he meant Ospho. It can be found in the paint section of a decent hardware store. We have at least one locally owned store here that carries it. It is green and comes in a one gallon clear plastic jug labeled OSPHO. You may find it under a different name. It is about $20 a gallon, but can be diluted and used over a few times. Wear gloves as it will warm up a hangnail or cut on your hands.
 
Muratic acid lesson.

A couple years ago I cleaned the rust out of the water jackets in a '56 Olds block. I used one of those cheap Harbor Freight sand blasters and stuck it in every water jacket port I could and blasted the crap out of the inside of it, most of the rust came out of there. My theory was the sand would bounce around in there and get to the spots I could not reach with the nozzle. I would say I got 90% of the rust out of there (I spent more time trying to flush the sand out of the block then I did sand blasting it). There were still some rust spots in there so I made a block off plate for the water pump and turned the block on its side and filled it up with a 50/50 mixture of muratic acid and water and filled the block completely to the top of the head gasket surface. It bubbled, gurgled and emitted all kinds of toxic fumes. I had to leave the garage door open overnight because I was afraid the place was going to blowup. You could smell the fumes block away. The neighbors probably thought I had a Meth lab in there to finance my hot rod projects. The next morning I found the muratic acid had expanded and overflowed all over the garage floor. It dissolved the cement about a ½-inch deep and just left the rock and sand. I had to patch the hole in the floor when I was done.

Later on I learned about hydrogen embritllement. I copied this from another site. “ Muriatic acid causes hydrogen embrittlement in carbon and alloy steel, cast iron, some stainless steels and aluminum alloys. During the "pickling" process, the material takes on available hydrogen atoms from the acid. This causes what is called "hydrogen embrittlement." Hydrogen embrittlement causes the material to fracture along sheer planes more easily. Thus, the strength of the part is greatly diminished.” Now I thinking muratic acid might not have been the best idea.

Here in CA the hot ticket used to be to take the block to Redi-Strip. Years ago I took an 8BA block to them and it came back looking like a NOS block. The EPA ran Redi-Strip out of California so they moved to Arizona. What ever process they were using was really slick, it was worth every penny they charged. The block looked like it just came out of the original mold.

I change the coolant on all my vehicles every two years, even the ones that sit in the garage and never move. If this is done the water jackets will stay like new forever. Changing your coolant is just as important as changing your oil. I don't buy that environmentally friendly coolant, I figure if you can drink it how good can it possibly be. I buy the most toxic green coolant with the biggest hazmat warning label money can buy to protect my vintage engines. I have a little farm here with lots of animals, I love animals and the enviroment probably more than the next guy but I love my flathead engines even more! I have a source for dropping off the used coolant to make sure it is properly recycled.

Jerry
 
I learned the hard way that muiactic acid removes no only the rust, but the base metal as well. It soaks into cast iron and will keep on destroying the base metal, even after repeated washings. It has to be nuetralized with a base such as ammonina. Better to use Ospho ( a registered trade mark) I buy the same essential product from my welding supply house, 4 one-gallon jugs to the box, about $28 per box. Each gallon is diluted with water to the strength you need. One gallon can make 3 to 10 gallons of "Ospho"! Ospho converts only the iron oxide, and leaves the base metal alone. Never used molassas, but have heard it works great, but parts must be soaked for many days to be effective.
 
I like the dry method. Have the engine baked to remove all the sludge, not hot tanked. When you get home put it on a 1/2 sheet of plywood, and go after all the cooling passages with a coat hanger. Next roll it around on the plywood, you can thump without hurting anything. Sweep off the wood and start over. This is not fun or clean but it gets the job done, Chuck.
 
Far and away the absolute, BEST, safest to you AND the block, and least destructive is the Oxalic acid. I would never use hydrocloric acid (aka Muriatic acid) or Phosphoric acid on the interior of an engine block. Oxalic acid is absolutely harmless to the cast iron block, but will dissolve every bit of the rust/scale in the block...and for that matter in the radiator, too. It has been used for decades as a heavy duty cooling system cleaner...and it does work great...
 
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The above methods seem to work well , I also use for the mechanical method of rust removal, a 5/16 or 3/8 inch by about 8 inch long steel cable with a copper or steel tubing
swedged at the end as to put in a drill and the other end swedged about 2 inches from the other end leaving about 1 1/2 of the cable exposed and then carefully insert the 2 inch end in the block and proceed to turn
the cable at low speed, the cable will fray out and the rust start coming loose,( BE CAREFUL AND DON'T LET THE CABLE TWIST UP AND GRAB YOUR HAND OR FINGERS)
as someone stated roll the block on plywood and empty out the rust and repeat as needed, then treat as desired with vinegar or what ever.
been using this method for years, and had good results.
fordestes
 
I just bought a rebuilt flathead. Everything looks OK except I do not know how much effort was spent cleaning the water jackets. It has Offy heads on it, so I know I don't want them on there if I do some sort of chemical cleaning. So, I'm thinking about installing some stock cast iron heads with some old head gaskets. I have the Speedway pressure test kit, so I could block off the water pump faces with those blocks or just put some rubber corks in the pump outlets. Definitely will use the diluted Ospho that Kerby recommends and just leave the head outlets open while things percolate. Thoughts on this? Will the Ospho do any harm to the pumps? Should I seal and torque the head gaskets like usual or will a nominal value like 30 pounds of torque work? About 2 days of setting? Thanks in advance. Lou
 
Certain engine shops have a "shake and bake" machine which heats up the block and shot peans it with media - comes out as clean inside and out as a new engine.
 
36tbird said:
I just bought a rebuilt flathead. Everything looks OK except I do not know how much effort was spent cleaning the water jackets. It has Offy heads on it, so I know I don't want them on there if I do some sort of chemical cleaning. So, I'm thinking about installing some stock cast iron heads with some old head gaskets. I have the Speedway pressure test kit, so I could block off the water pump faces with those blocks or just put some rubber corks in the pump outlets. Definitely will use the diluted Ospho that Kerby recommends and just leave the head outlets open while things percolate. Thoughts on this? Will the Ospho do any harm to the pumps? Should I seal and torque the head gaskets like usual or will a nominal value like 30 pounds of torque work? About 2 days of setting? Thanks in advance. Lou
Click to expand...

Lou
On one that has already been assembled, I'd be paranoid for fear a small leak would form and get in someplace I didn't want it. I don't know how well the water pump seals would handle it either. In any case you'd have to be careful to preserve everything else. You have to rinse it out good too. It would be a challenge for sure.

You might consider doing a cooling system flush after the engine is ready to run and using a milder mix like vinegar (acetic acid). You could do that with a lot less trouble.
 
Go to your local Livestock feed store and get Molassa. 4 parts water with one part molassa and nothing gets eaten up. The warmer the better, summer at 90 degrees is best. Pour it on lawn when your done. Dave/Green Bay
 
Good luck with the 53 Roy.I enjoyed talking to you on the phone. You folks on the barn reinstall that burning desire to keep me moving on my Projects. Please contact me ,here on the barn or call I need to know what worked for you. got to do something with my 53 mercury. Got to get the 52 truck,52 car 38 dont know what car it came out of welding machine flathead out of the way first. So many flatheads not enought time. May you all be blessed! Lyle
 
Many years ago I used muratic acid in my garage for something (can't remember for what). Next day I go in and any exposed steel surfaces had a rust type coating. Never used it again.
 
About 20 years ago,my Rolls Royce 20/25 was apart for an overhaul.There was a huge boiler plate on the detachable block assembly with about a thousand screws holding it on.I scraped,chisled and worked on the critter till I knew beyond a reasonable doubt I had all the scale removed.WRONG! I did this process over and over.English water must have more scale-causing properties than our water.All the above remidies will work.Good skill,fellows!
 
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