Heat Exchanger Zinc Corrosion problems. Looking for advice.

[Group_er]

Hey guys,

I replaced my zinc in my heat exchanger for the first time about a year ago. It was fairly corroded on the outside of the plug the holds the zinc, and the zinc was pretty much gone. I could see green and white corrosion, and it had actually been leaking slightly onto my raw water pump below. I replaced the plug and the zinc and used a healthy dose of liquid thread sealant. Aprox 6 months later (this past fall) I noticed the plug that holds the zinc was still leaking ever so slightly, and there was a lot of corrosion on the outside of the plug. I replaced both the plug and zinc again, and used a healthy dose of liquid sealant. I was doing my spring maintainance this weekend and noticed it was still leaking ever so slightly, and the outside of the plug was of course corroded again. So again, this weekend, I replaced the plug, the zinc, but this time used thread sealant tape. I just checked it, and there is slight corrosion starting already. The corrosion isnt actually on the plug but right beside it, on the bung of the heat exchanger. I will try and take a picture tomorrow and post it.
Can anybody give me some advice as to whats causing this? How long should a zinc last in a heat exchanger?
thanks for any help guys!

 

[cecho]

Re: Heat Exchanger Zinc Corrosion problems. Looking for advice.

Could the thread sealant / tape be preventing a good contact between the zinc and the heat changer? Without a good electrical contact the anodes don't work.

 

[achris]

Re: Heat Exchanger Zinc Corrosion problems. Looking for advice.

Please tell us what you are working on. I'm not aware of any Mercruiser heat exchangers with sacrificial anodes in them.

One more thing.... If you just keep replacing the plug without finding out WHY it's leaking, it's just going to continue to leak....

Chris.....

 

[dan t.]

Re: Heat Exchanger Zinc Corrosion problems. Looking for advice.

I have a stock Merc heat exchanger with the 1/8 thread pencil anode, I change it every 3 months. Generaly not much left,I drilled and tapped the drain holes in the risers to take the 1/4 thread plugs and anodes, they will last a year, the stock 1/8 dont last very long. BTW i always use Permatex thread sealer, the anodes dissapear so I presume they are making contact. Check if your heat exchanger is grounded to the block, I dont know if that would cause the corrosion but its worth checking.

 

[Group_er]

Re: Heat Exchanger Zinc Corrosion problems. Looking for advice.

Thanks for the info guys. Its a 1995 7.4L carbed. I will Stop using thread sealent to acheive a better connection. Do the risers take a factory zinc? I only know of the one zinc for my motor. I am almost positive that my heach exchanger is sitting on rubber in the brackets with two stainless large hoseclamps attaching it to the bracket. If the hoseclamps are not conducting thru the bracket and heatexchanger paint, It woulld definitly not be grounded to my motor.... I guess I should check ah?!
Thanks agaain guys.
Ill try and take some pics today!

 

[achris]

Re: Heat Exchanger Zinc Corrosion problems. Looking for advice.

Thanks for the info guys. Its a 1995 7.4L carbed. I will Stop using thread sealent to acheive a better connection. Do the risers take a factory zinc? I only know of the one zinc for my motor. I am almost positive that my heach exchanger is sitting on rubber in the brackets with two stainless large hoseclamps attaching it to the bracket. If the hoseclamps are not conducting thru the bracket and heatexchanger paint, It woulld definitly not be grounded to my motor.... I guess I should check ah?!
Thanks agaain guys.
Ill try and take some pics today!

It doesn't have to be grounded to the engine. There just has to be an electrical connection between the zinc and the heat exchanger. In fact, if you have a connection between the heat exchanger and the engine block, the zinc will then try to protect the engine block too, which would explain why they are eroding so quickly. I would leave the rubber strips there, and get some thin rubber tubing and slip it over the hose clamps, and make sure it is NOT grounded to the engine block....

Chris.........

 

[dan t.]

Re: Heat Exchanger Zinc Corrosion problems. Looking for advice.

The riser drains may not come with anodes but generaly there is room for a pencil anode ,any anode you can get in the raw water system will make it last that much longer.

 

[Group_er]

Re: Heat Exchanger Zinc Corrosion problems. Looking for advice.

Ok thanks guys.
I went to the boat yesterday to take some pics, but they turned out horrible.
Ill post them anyways, but heres were the corrosion is coming from after only a week, or a bit less...

 

[dan t.]

Re: Heat Exchanger Zinc Corrosion problems. Looking for advice.

Over tightened and a crack in the nut perhaps.

 

[elkhunter338]

Re: Heat Exchanger Zinc Corrosion problems. Looking for advice.

My guess is the end cap on heat exchanger might be the leak. Rubber shrinks and gets old. my head exchanger has a rubber seal on the end and I have had to tighten the bolt holding the end cap on.
Also I use electrical corrosion guard grease on my zinc plug threads. Give good electrical connection and prevent corrosion.
I have my exchanger grounded to the engine block, which connects to the battery my guess is probably a connection to the alum boat.
I catch fish and not corrosion problems on the hull.