Soaking A Corroded Heat Exchanger

Our heat exchanger ... taking a soak.

As I mentioned in our post about replacing the engine's pencil zinc, we realized that the heat exchanger had a lot of corrosion in the hole where the zinc screws into.  Since there was so much corrosion, we figured it was time to remove and clean the heat exchanger before going any further.  

Ken removed the heat exchanger by making the sure the water valve was off, draining the coolant (not easy when there's no room underneath to catch it), then disconnecting the hoses.  He had containers to catch anything left in the hoses, and towels to clean up the inevitable mess.  The heat exchanger was then unscrewed from the clamps and removed.  The picture below shows the missing heat exchanger.

When Ken removed the heat exchanger and the end caps, he knew that he'd made the right decision to have it cleaned.  I wish we would have gotten a picture, but the tubes inside of the exchanger were also heavily corroded.  Ken planned on having a local radiator shop boil the heat exchanger, but none of them boil anything these days.   However, Ken did receive some advice from one of the radiator shops ... soak the heat exchanger in something with phosphoric acid (NOT muratic acid).  He recommended a product called Chemprime, which Ken found at the local hardware store.  

Chemprime ... and the old gaskets removed from the heat exchanger's end caps.

Using rubber gloves, Ken poured the Chemprime into a plastic container then placed the heat exchanger into the solution.  The Chemprime was a bright green liquid, which quickly started turning brown as it removed the rust and corrosion (first picture above).  About every hour Ken flipped the heat exchanger, letting it soak for about 4 hours.  He then rinsed the heat exchanger in water and wiped it dry.  Voila ... no more corrosion!

With the end caps removed (before soaking), you can see that the tubes inside are free from corrosion.

Since using this product, I've since learned that it's been used in the Louisiana and Texas oil fields for over 30 years!  Chemprime converts rust into a protective coating which can then be painted.  Just clean the surface, rub or spray on the Chemprime, then let it dry.  The rust will be converted into a white ceramic-like protective compound.

  This stuff sounds great!  It's supposed to clean and protect rusty tools and all sorts of other stuff.  It also claims to be good for cleaning out gas tanks.  I learned that this stuff even renews the grout on tile floors!  Just spray it on the tile floor, let it sit for an hour, then mop.  I'm going to try this on our rental someday.  With all the rust we've been seeing around our engine, I think we'll buy some more Chemprime and try spraying it on a few things.

The hole where the zinc goes was so full of corrosion that a pencil couldn't have fit through it ... now all of that corrosion is gone.  So now we can put that zinc in there ... or so we thought.  Ken bought two brass heads and a few anodes to screw into them for spares.  This will be cheaper than replacing the entire zinc every time it needs to be replaced.  Would you believe that the dang thing still doesn't fit?!  While we have no regrets cleaning our heat exchanger, the zinc is what started this whole project and it should fit.  Ken had to cut one of the new zincs in half ... surely that would do the trick.  Nope!

Ken proceeded to grind the zinc into a pencil ... literally a pencil zinc now.  That didn't work either.  Why won't this zinc fit?  Any smaller and there won't be any protection!  After looking closely at the exchanger, we think that the piece attached on the end of our Westerbeke heat exchanger may have been improperly placed.  If you look at this picture below, the zinc isn't screwed all the way in but it's still hitting the metal.  The same piece of metal on the left side of the exchanger is thinner.  Was this piece put on backwards?  Was it put in the wrong position?!  We'd love to hear your thoughts, and in the meantime I'm going to email Westerbeke a couple of pictures and see what they say.  

Other than the issue with the zinc, the next step is installing the heat exchanger ... or is it?  Ken has been thinking about whether or not he should re-paint the exchanger.  It looks to have been previously painted with a bronze paint, which has started to come off in spots.  After cleaning the exchanger, Ken lightly sanded it and removed most of the remaining paint.  He wishes that he'd thought of sanding the exchanger before soaking it in Chemprime, but since he didn't I'm thinking that he could just clean the exchanger with some detergent, spray it with Chemprime and let it dry.  Tell me if I'm wrong, but it's my understanding that the Chemprime should be enough of a protectant.  Many of the reviews I've read about this product mention spraying it on car parts and just leaving it.

So, the project continues!  I think Ken will be installing the heat exchanger real soon without any new paint and with a really short zinc for now.  He's already purchased the new gaskets and O-rings for the end caps, as well as some new hoses and clamps.  We're anxious to go sailing before Summer is over.  Oh, and one more thing about the zinc ... we've heard that teflon tape should NOT be used on the threads because the zinc needs metal-to-metal contact in order to be effective.  Thought I'd pass that bit of info on to ya.

Hasta luego ... until then.  Mid-Life Cruising!