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Heat Exchanger Corrosion

NGB

Member II
My 1987 Universal MK 12 engine runs fine, and the heat exchanger appears to be doing its job. Recently, however, I decided to change the zinc in the exchanger. I do not know when it was last changed. When I took it out, there was no zinc left, only the threaded part. When I tried to replace it with a new zinc, there was an obstruction and the zinc would not go in.

I am assuming the obstruction is a corrosion layer that has covered the hole and is not an integral baffle or other part of the exchanger. I was considering trying to drill through it until it will accept a zinc. Does that sound like a reasonable approach, or a really dumb idea? I don't want to ruin the exchanger, but, without correcting this, sooner or later I will have to replace it.
 

stbdtack

Member III
Dont drill into the hole! Maybe try gently pushing a wire or screwdiver in. if it's corrosion it should be easy to push through it. I found that the std zinc I bought at West Marine was slightly too long to fit into my 5432 heat exchanger. I just cut about 3/16" off the end. Maybe try to look in with a mirror and flashlight to see if it's blocked first.
 

Sean Engle

Your Friendly Administrator
Administrator
Founder
I would yank out the exchanger and try to flush it out (and see if you can see the blockage).

Then, once you've seen all the crud in there, and start feeling guilty for making your engine deal with it, you'll be half way done in replacing it with a new one! :p

Honestly - the other choice is to have it boiled out - to have all that crud blown out. Do you know how old the exchanger is? Mine rotted all the way through - and was preceeded by increasing operating temperatures - until one day all my coolant disappeared. Purchased a new one, and the engine ran much cooler.

//sse
 

jmoses

Member III
Two things, remove the exchanger and let it sit in a bucket of 50/50 muriatic acid and water over night - you'll be amazed at how well this works. Once this is complete, install the unit and insert a new zinc (keep in mind some zincs are too long and will have to be cut to fit).

John M.
 

stbdtack

Member III
Acid....

I wouldnt leave it in acid overnight. I found that 5 minutes cleaned mine out just fine. Blast it out with a hose and soak in fresh water for at least 15 minutes to get all the acid diluted. Soak in acid another 5 minutes if its still clogged. More important is to agitate the acid inside to get the stuff loose.

If you leave it overnight you may not have anything left in the morning. Muratic acid is pretty corrosive.
 

diamondjim

Member II
Acid soak

Don't forget to add some baking soda in the fresh water rinse to nuetralize the acid!
For a more gentle approach, try vinegar! This method was used in Eastern Block countries because they could not get standard flush products.
 

NGB

Member II
Thank you all for your suggestions. I will get down to our boat on Friday and see what taking the exchanger off and cleaning it out involves. You have convinced me that is the best thing to do. (There is nothing I enjoy more than trying to wrap my aging, 6'4" body into the engine compartment. I better go easy on the pecan pie tomorrow.)

The information I have gained from this site over the past couple of years has been invaluable to me, and I thank you one and all.
 

jmoses

Member III
5 minutes?

5 minutes in a dilute solution of 50/50 water/muriatic acid will do little to nothing to clean the crud off a well contaminated heat exchanger. Considering I have done numerous heat exchangers this way (dozens) and have had no problems in 15 years, I think it's quite safe to do a 50/50 solution overnight. In fact, some heavily contaminated exchangers took several baths over a period of days to clean all the crud off them. Come to think of it, we would dip engine blocks in a nasty acid solution for quite some time depending on the level of contamination. This 'dip' solution was very acidic (hello EPA) and if a part came out with a hole in it, then it was due to electrolysis/casting defect and not the acid.

After all, if you have a swimming pool, you'll soon realize you are swiming in a muriatic acid and chlorine bath, albeit rather dilute....However, if it's a public pool, well then, look out as you are swimming in a heavily dosed muriatic/chlorine solution (worked on pools in college).

However, the idea of dosing the rinse water with baking soda to neutralize the acid is an excellent one. In addition, vinegar will work to some degree if the exchanger has light build up - head to Costco and get the 2 gallon pack, otherwise it's not cost effective. Regardless, do NOT dump the muriatic acid solution into the water...dispose of properly!
 

chaco

Member III
Zinc Plug

Well it just so happened that my HX had the same obstruction :eek: !
In the process of cleaning and inspection I removed the old zinc
and discovered a wee zinc plug left in the hole. This is what is left
when the zinc needs to be replaced. I also found corrosion inside the
HX head left from the zinc. My conclusion is that when your zinc
needs to be replaced you should remove the head cover, inspect
for corrosion and remove it. I have the luxury of the HX being removed
from the engine and will proceed to the acid cleaning phase.
The zinc plug was easily removed via screw driver and the threads
cleaned with a wire brush....be carefull of the threads they are soft
copper/brass and damage easily.
Oh the little mysteries in life ! :egrin:

Dan
E35-II
Merlin
Oceanside Harbor, CA
 

Brookelise

Member II
Order of parts in heat exchanger

In the 3-inch diameter heat exchanger, do the small black rubber O-rings around the bolt go inside the metal cap at each end, between the cap and the rubber gasket?

In other words, do the parts go like this: Bolt, then metal cap on heat exchanger, then O-ring, then rubber gasket, then heat exchanger cylinder?


Thanks for any help.

-- Brooke
E34
 
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