Zinc anodes in heat excahnger

[brico]

Hi I just checked the zinc anode in the raw water side entrance to the heat exchanger and when I removed the plug nothing came out with it. The hole appeared plugged with wasted remnants of the zinc anode. When I poked it a bit it cleared and some water escaped out. Guess this was left unchecked for a long time and I only got the boat a month ago.
Few of questions.
How often should these be renewed? What governs the rate of depletion of these anodes, time immersed in sea water or the volume of water that passes through the exchanger? Could this be the cause of reduced flow of raw water through the exhaust (which I have confirmed by observation)? How many are there on the DD-6-71s?

[workingonadream]

unless you have a few of them laying around in there I don't think you would have a flow problem. how are you noticing the flow problem, are you just looking at the exhaust at idle ,are you running hot and that side appears to be dumping less water than the other the reason I ask is because I thought I had a similar problem a few years ago and unless there is a major difference in flow from both exhausts it is difficult to pinpoint. I fixed my problem but my port side still appears to be dumping less than the starboard and everything is still fine. I would rip those exchangers apart and clean out those old zincs before pieces of them get further on down the line and boil out the exchanger itself especially if you are running hot or at the minimum that you now have a baseline of when it was done. good luck

[bostonhatteras]

Overheating is probably the one single worst thing that can happen to a Detroit. Much over 200 and the engine gets really unhappy. they need to run at 180 degrees. I think the alarm temp setting is 195. If the water flow out of the exhaust is weak maybe you should check the raw water impellors. There should be a zinc at the raw water pump and one or two zincs in the heat exchanger. a good thing to have is a 3/4 pipe thread tap to clean the threads the zinc goes into for a good electrical connection. zincs wont work without being 'electrically' connected to what they are there to protect. Even small amounts of fouling on the heat exchangers can have a big impact on operating temps at load.

[bobk]

I can get six months from mine, but choose to replace at 3-4 months. The zincs are cheap by them selves. The plugs get pricey. If you change frequently, you are likely to easily unscrew the old zinc from the plug. If you wait, they break off and you either need to buy the entire thing, or spend a lot of time drilling and tapping to get the old out. The pencils are less than $3 each at Lewis Marine here in Stuart.

BTW, you can easily check electrical connectivity with an ohm meter when you assemble it.

Bobk

[doc g]

quick little trick--to remove the Zn from the plug after it's broken off. I submerge them in phosphoric acid like you would use to clean the HE's on the an engine . Takes about a day but when you rinse it off nothing but brass left , no drilling,tapping or fussing around . Normal acid precautions like make sure it can't spill and ruin anything, do it outside etc......Pat

[MikeP]

Lot's of folks do not use any zincs in the HE (or RW pump). Many modern engines used for marine operations do not even have a location for zincs…

But do whatever you are comfortable doing.

[Bugsy]

Just want to second what was said above. When a zinc breaks off into the HE, it is important to flush the system and remove the remnants because they WILL reduce the effectiveness of the HE and WILL increase operating temperature.

And you do not want the high-heat alarm to sound because when it does, you've already over-heated. With VERY negative consequences.

[bobk]

quick little trick--to remove the Zn from the plug after it's broken off. I submerge them in phosphoric acid like you would use to clean the HE's on the an engine . Takes about a day but when you rinse it off nothing but brass left , no drilling,tapping or fussing around . Normal acid precautions like make sure it can't spill and ruin anything, do it outside etc......Pat

I used to dissolve them out with acid, but I made up a drill guide to allow me to bore a tap hole dead center. After drilling, I simply chase with the tap. A quick acid dunk and it's ready to go. But, still easier to change often.

Bobk

[brico]

Thank you all guys on feedback regarding renewal of zincs and potential clogging of HEs by remaining zinc anodes that disintegrate. I am positive about at least one of the HE anodes disintegrating. Now when it comes to clogging the JE and the flow of raw water through it, i am not sure unless i open the HE up for inspection and cleaning.

I run the boat with my 1980 DD 6071 engines up to 1500 RPM without any steam and heating. In fact the temps are way below 180F. Once I venture close to and above 2000 RPM the steam starts coming out and the temperature comes to close to 180F but not over that and no alarms sounds. It is somewhat difficult to positively ascertain the difference in exhaust water flow at higher boat speed so as I said in my original post, i have positively observed the significant raw water flow difference while at the dock at 2000RPM while out of gear tied up at the dock (no steam was coming out then as no load on the engines) Starboard engine (the one that steams up while driving the bot hard) exhaust discharge was about 1.5 feet away from the boat transom while the Port engine discharge was about 2.5 to 3 feet from the boat transom.

Guess i'll have to open up the delivery side of the raw water pump as the pump casing and impeller were inspected and no issues were observed.

[workingonadream]

I don't think that it is a big deal jf both engines are running the same temp at the same rpms I don't think you have a flow problem I chased this ghost before and you may drive yourself crazy. like I said before my port looks like there is less flow than stbd, but they run at the same temp with everything being equal ie impeller age and h/e cleaning. I would clean both heat exchangers take it for a ride and see where the temp is. I would be more worried about cleaning out all that zinc residue first and go from there good luck