View Full Version : Removing Rust from Cooling System

01-27-2016, 12:23 PM
I am hearing some mixed advice for removing some rust from the cooling jackets in an engine block. I searched through here and did not see much posted, unless I missed something.

I have the head off and all jackets are exposed. When I cleaned the rust from my fuel tank I soaked it in vinegar with much success. It seems here I need a flushing agent of some sort. I have seen some use diluted citric acid, others with just coolant flush.


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01-27-2016, 05:48 PM
I remember seeing something about this on another site when I was asking about rust in the flathead motor that I got when I bought an old 49 ford. One of the items that someone mentioned was using muriatic acid. Here is a quote I found about that process.

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.

It might be better to have the block professionally dipped. I know that using vinegar breaks up the rust, but it will sooner than later show up in your radiator.


Jeff W
01-27-2016, 09:25 PM
I don't think with just the head off you have any better access to the water passages. I would just reassemble and then use a commercial radiator cleaner following the directions.

Larry's post scares me away from home concoctions.

01-27-2016, 10:30 PM
You could try one of these coolant filters to keep stuff out of the radiator that might shake loose later.

01-28-2016, 10:26 AM
A little rust in the water jackets is pretty normal. I'm with Jeff here - just put it together and use a standard Prestone flush. Add the kit too if you really want to purge it all. Use of antifreeze has the good rust inhibitor to keep rust at bay.

It is only heavy scale-rust, where a heavy-duty cleaner should be used. The filter might be a good idea, but I don't think that is something you will have to worry about. Usually, by the time you might be thinking this is needed, there is more rust in the block, settling in the lower ends of the block, that freeze plugs may want to get popped and a good evacuation of that sediment is done too. You can only get so much sediment out with a flush kit. Ask me how I know.


More often than not rust (that is bad enough to worry about) is from not being proactive with periodic cleaning of the old antifreeze and rust that forms from all the other things that corrode as well, like the lower hose spring, pump impeller. Antifreeze should be checked a lot more than most of us think to do it.

01-28-2016, 10:35 AM
Probably wouldn't be a bad idea to perform a regular electrolysis check too. Particularly if there is any aluminum in the cooling system.

01-28-2016, 10:57 AM
Since the cooling system is apart anyway, I am going to try flushing manually with a coolant system cleaner and using a brush wherever I can reach. I am going to pull the block drain as well as thermostat housing and see how much crud I can remove.

I like Jeff's idea as well and will do so after a good manual cleaning of the components while it is apart. The good news is that when I drained the system the radiator seemed to have free flow.

01-28-2016, 05:21 PM
Just be careful not to get water down the oil holes...

02-02-2016, 09:17 AM
I heeded all warnings. I carefully flushed the block and radiator with hot water until it came out clear. I am going to pull the thermostat housing and water pump to carefully clean them, run hot water through the heater core, then call it good until reassembly. The freeze plugs look good and all else seems to be checking out.

02-02-2016, 01:43 PM
Hmm... and all this time I thought your motor was pretty new. Not sure why I thought that, but the picture would indicate otherwise.

That looks pretty normal for water-only coming from a block. Left there overnight fresh water would do the same. Lots of raw cast-iron in the water jackets. Takes no time at all to turn brown. That's why you add green.