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Old 04-12-2017, 10:57 PM   #1
Chris Haynes
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Default Block cleaning

I am going to R&R my head to add a higher compression unit. So today I disconnected the radiator hoses. Plugged the inlet hose on the side of the block then poured in a gallon of Muriatic acid. I let it sit for a few hours then removed the plug and let it drain. Stuck the hose in the outlet on the head and flushed out huge chunks of rust and grime. A flashlight in the block shows clean bare metal. Tomorrow I will switch the head and fill it with coolant and anti rust. Hopefully it will run cooler.
I guess it would be a good time to back flush the radiator too.
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Old 04-12-2017, 11:03 PM   #2
Tom Wesenberg
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Default Re: Block cleaning

I would never pour in muriatic acid. It will continue to eat the metal unless it's very well neutralized. Even the fumes from muriatic acid will quickly rust metal for several feet around. I'd pour in Evaporust and let it set for a few days.
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Old 04-12-2017, 11:30 PM   #3
daveymc29
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Default Re: Block cleaning

I used vinegar and let it sit a month, then back flushed the block only, then the radiator only. Lots of rust came out and I refilled with water and a cup of baking soda. Ran it a day or two and repeated the flushing, then did it again. After the third flushing I filled the works with 50/50 antifreeze. I also installed a 160 degree thermostat in the upper hose, just above the water pump. (S0 far it hasn't moved) I had soldered the stat to a rolled piece of copper that I had made into a 1.5 inch pipe just barely able to pound into the hose. Seems to be working fine and so far no rust appearing in the antifreeze.Temperature after running a half hour or so is slightly higher than it was without the thermostat, but just about 180 in the upper hose above the thermostat. Usually 165 on the lower hose.
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Old 04-13-2017, 12:14 AM   #4
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Default Re: Block cleaning

Any block that has been marinated in a gallon of muriatic needs to be rinsed well then marinated again in a solution of one pound of baking soda per gallon of water to neutralize the acid. As noted by a previous writer, muriatic acid will just keep on dissolving iron if not neutralized.

I saw a low mileage but very rusty diamond Model B block that received a stout bath in muriatic acid continue to dissolve over the course of a year. The guy that owned it commented on all the rust that fell out of it every time he moved it. By the time he took it in for boring and rebabbitting there were pin holes appearing in the top deck.
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Old 04-13-2017, 02:54 PM   #5
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Default Re: Block cleaning

Would certainly agree with others. At a minimum, flush entire cooling system with clean water several times. Adding baking soda on initial flushings can only help. Only when you're sure it's thoroughly flushed and neutralized, drain and add coolant.
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Old 04-13-2017, 04:33 PM   #6
Dollar Bill
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Default Re: Block cleaning

Not to pile on but comment for posterity. The problem is that although HCI will remove the rust you see (actually what you see is NOT rust, it is the already oxidized byproduct of the rusting process which you can not see) it will set in motion a process that will lead to more damage even though it appears as clean bare metal right now. Once the acid contaminates the iron (ESPECIALLY cast iron which tend to be somewhat porous) the chemical reaction that starts will be nearly impossible to stop. Some will say you simply need to neutralize the acid, much easier said than done, and while steps to do this will slow the damage it hardly ever stops it completely. The rust converter solutions both dissolve the oxide on the surface and form a phosphate that tends to stop the rusting process, the Hydrochloric (Muriatic) acid on the other hand will dissolve the oxides but as far as stopping the rusting process it will be like throwing gasoline on a fire! Once the metal is contaminated with HCI, it can really make a mess. It is not as simple as removing the iron oxides that you can see you must take into account the chemical process that you have started. In the future, use Phosphoric acid because it will remove the oxides and start the right chemical reaction that will leave a phosphate coating that will inhibit rust instead of accelerating it. The Phosphoric acid may take a little longer but it is definitely the better way to go.
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Old 04-14-2017, 12:54 PM   #7
Chris Haynes
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Default Re: Block cleaning

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Originally Posted by wk2w View Post
Would certainly agree with others. At a minimum, flush entire cooling system with clean water several times. Adding baking soda on initial flushings can only help. Only when you're sure it's thoroughly flushed and neutralized, drain and add coolant.
Done repeatedly. :-)
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Old 04-14-2017, 01:16 PM   #8
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Default Re: Block cleaning

Not only bad with cast, but high carbon alloy steels are subject to hydrogen embittlement. Which can be caused by any acid, but HCL is the harshest.
The hydrogen can work its was in to the molecular structure of the steel and combine with it and form a gas that will build up enough pressure to break hardened steel.

The plating industry is very cautious of this problem. It doesn't hurt to study it out a bit.
A materials/metallurgist friend of mine in the nuclear industry assured me that a quick wash to clean wouldn't do any damage.(I am referring to hardened steel, not cast)

I am pretty anal, I would run water with baking soda for a while in the engine
if it had any Hcl put in it, just to be sure, then flush with phosphoric if nervous about rust.

Last edited by 30 Tudor; 04-14-2017 at 08:01 PM.
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Old 04-14-2017, 07:53 PM   #9
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Default Re: Block cleaning

So...what does the original poster, Chris; have to say?
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Old 04-14-2017, 10:13 PM   #10
Chris Haynes
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Default Re: Block cleaning

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Originally Posted by Brian in Wheeling View Post
So...what does the original poster, Chris; have to say?
Brian
I can't say anything other than what I posted above. Cleaned, rinsed repeatedly with BS and water, then lots of water. Now my radiator is full of vinegar in an attempt to get all the rust out of it.
The next thing will be getting my beat up old radiator re-cored.

PS I just noticed that the vinegar I bought at Costco is only 5% acid. Its not working very well.
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Old 04-14-2017, 10:30 PM   #11
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Default Re: Block cleaning

Vinegar takes a lot of time to do it's thing. I ran it straight for a few days and I know it wasn't long enough to do much good, so patience is your best virtue. I did quite a few flushes after dropping it pulled the lower connection off to give it a fast dump and refilled with 50/50 coolant. I know glycol can make it run 20 degrees hotter but the 3 row tube and 10 fpi recore has proven itself to be adequate. I also have a 160 thermostat as close as possible to the upper neck.
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Old 04-14-2017, 11:31 PM   #12
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Default Re: Block cleaning

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Originally Posted by Chris Haynes View Post
I can't say anything other than what I posted above. Cleaned, rinsed repeatedly with BS and water, then lots of water. Now my radiator is full of vinegar in an attempt to get all the rust out of it.
The next thing will be getting my beat up old radiator re-cored.

PS I just noticed that the vinegar I bought at Costco is only 5% acid. Its not working very well.
I had to run the vinegar for 30 days to get the rust flakes out of my system, and even then I used a sump pump to back flush the block and radiator and got out some more junk. If I ever have to do this again I will use Evaporust.
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Old 04-15-2017, 12:41 AM   #13
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Default Re: Block cleaning

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Originally Posted by Tom Wesenberg View Post
I had to run the vinegar for 30 days to get the rust flakes out of my system, and even then I used a sump pump to back flush the block and radiator and got out some more junk. If I ever have to do this again I will use Evaporust.
Evapo-rust is 23 bucks a gallon. I'll wait on the vinegar to do ts job.
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Old 04-15-2017, 01:00 AM   #14
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Default Re: Block cleaning

Chris, when you remove the head look at the back of the block. Behind Number 4 there might be some blockage. I used a probe and air to clear it. Put rags in the cylinders first.
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Old 04-15-2017, 01:13 AM   #15
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Default Re: Block cleaning

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Originally Posted by Chris Haynes View Post
Evapo-rust is 23 bucks a gallon. I'll wait on the vinegar to do ts job.
That's the drawback.
I wonder how molasses would work? I've used it to derust some other parts, and it did a good job.
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Old 04-15-2017, 01:15 AM   #16
Chris Haynes
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Default Re: Block cleaning

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Originally Posted by Brentwood Bob View Post
Chris, when you remove the head look at the back of the block. Behind Number 4 there might be some blockage. I used a probe and air to clear it. Put rags in the cylinders first.
Bob
Thanks for the tip.
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Old 04-15-2017, 05:43 AM   #17
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Default Re: Block cleaning

Vinegar is one of the cheaper/safer/time consuming solutions for rust removal but it will leave debris in your cooling system and flash rusting will result in rust colored coolant until the block is passivated.

Phosphoric Acid will clean and convert rust but will not remove rust chunks.

Evaporust type products are chelation agents that bind tightly to oxidized iron and pull it into solution so there will be no chunks left behind as with acids.

Iíve used both Evapo-Rust and this much cheaper version and cannot tell the difference other than cost.

Chelation agents are the more costly solution but provide the best results - They can also be used more than once.
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Old 04-15-2017, 07:09 AM   #18
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Default Re: Block cleaning

Thanks for the link to RUST 911.
That looks like the thing to buy, and I'll use that the next time I need to derust a block.
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Old 04-15-2017, 12:45 PM   #19
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Default Re: Block cleaning

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Thanks for the link to RUST 911.
That looks like the thing to buy, and I'll use that the next time I need to derust a block.
I've used Rust911 for 5 yrs. with superb results. It is an excellent product.I just do not understand why people play around with acids when this superior product is available. Works really well to derust the inside of the gas tank. It comes out spotless.
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Old 04-15-2017, 07:24 PM   #20
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Default Re: Block cleaning

PS I just noticed that the vinegar I bought at Costco is only 5% acid. Its not working very well.


5% is normal for vinegar

I left it for 6 weeks in my 12 Buick radiator and it did a marvelous job! cleaned it out good.

Patience is a virtue.
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