What is happening to my heat exchanger?

[er9]

a few months ago I removed it, completely removed all the paint back to bare copper, primed and painted it. I also soaked and cleaned the inside of it and replaced the zinc with a brand new one.

today was poking my head in engine compartment t and noticed a large white growth around the outside of the zinc bolt. it also corroded all the paint around the outside of the zinc.

what happened? the only thing I can think of was that I didnt screw the zinc in tight enough and salty water is seeping past the threads and that the white fluffy growth is salt?

[Wotname]

Originally Posted by er9

a few months ago I removed it, completely removed all the paint back to bare copper, primed and painted it. I also soaked and cleaned the inside of it and replaced the zinc with a brand new one.

today was poking my head in engine compartment t and noticed a large white growth around the outside of the zinc bolt. it also corroded all the paint around the outside of the zinc.

what happened? the only thing I can think of was that I didnt screw the zinc in tight enough and salty water is seeping past the threads and that the white fluffy growth is salt?

Possibly correct and if so, the white stuff could well be a calcium salt, it precipitates out of seawater when it is heated.

[Snore]

Originally Posted by Wotname

Possibly correct and if so, the white stuff could well be a calcium salt, it precipitates out of seawater when it is heated.

So close. As you may recall from high school chemistry- The ability to hold salt in solution is temperature dependent. So hot water can hold more salt in solution.

The growth is likely from a slow leak that evaporated and leaves the salt behind.

[er9]

thanks guys. I'll pull the zinc this weekend and clean it up. ok to put teflon tape on the zinc threads? cant imagine it would hurt but I've heard teflon tape can prevent a water tight seal on certain thread types.

[Gary Matthesen]

Maybe on the threads but you want an electrical connection for the zinc to act as an anode.

[Squanderbucks]

Clean with wire brush after removal and use rectorseal thread sealant on the threads. Teflon is ok too but I prefer the rectorseal. It is an old wives tale that using a sealant in the threads blocks conductivity. There is enough metal to metal cut through the sealants time allow the zincs or oil pressure senders to work properly.

[er9]

got it...thanks.

[Gary Matthesen]

Just the same, acknowledge there needs to be electrical contact.

[FL Dan]

Threads cut right through the Teflon tale and conductivity is not an issue. For peace of mind, just do a quick continuity check with a VOM.

[a64pilot]

Originally Posted by Snore

So close. As you may recall from high school chemistry- The ability to hold salt in solution is temperature dependent. So hot water can hold more salt in solution.

The growth is likely from a slow leak that evaporated and leaves the salt behind.

True, but something that is not salt precipitates out of Sea water when it’s heated above a certain temp, this is why raw water engines run so cool.
This something that is I believe calcium carbonate, won’t dissolve back into water either, whether it’s hot or cold, we have all seen it in our heat exchangers.

I’ve often wondered why cold water will hold more oxygen than warm water too, it would seem that warm should?

[GordMay]

The white deposit is zinc oxide.

[FL Dan]

Originally Posted by FL Dan

Threads cut right through the Teflon tale and conductivity is not an issue. For peace of mind, just do a quick continuity check with a VOM.

"tape", not "tale"

[a64pilot]

Originally Posted by GordMay

The white deposit is zinc oxide.

What is the source of the zinc?

[Wotname]

Originally Posted by Snore

So close. As you may recall from high school chemistry- The ability to hold salt in solution is temperature dependent. So hot water can hold more salt in solution.

The growth is likely from a slow leak that evaporated and leaves the salt behind.

So close.

As you may recall from university chemistry - not all salt solutions act the same way. Calcium carbonate is unusual in that its solubility decreases as the temperature of the water increases.

IIRC, various magnesium salts are similar.

This is principle reason why boiler scale is such a problem and raw water engines have to be operated at lower temperatures (usually around 50C).

EDIT: I note a65pilot answered this back in post #10; note to self, read all replies before posting. Salt in this conversation is used in it's chemistry meaning. Common table salt (NaCl) is just one of many salts found in sea water.

[Wotname]

Originally Posted by a64pilot

What is the source of the zinc?

Anode?????