Broken heat exchanger zinc

[tvorgitch]

I went to inspect the heat exchanger zinc on my M35 and it snapped off. I thought maybe the whole thing had been eaten away as I had not inspected it since I purchased the boat in August 2021 (I know!). No water came out when I removed the nut and I was unable to insert a new zinc. Using my phone, I could see the hole was plugged by what looks like the rest of the zinc. I put the nut back and did not observe any leaks.

The PO had a receipt for work done in October 2020 that included "inspect heat exchanger" but give the shoddy work the yard did on the cutless bearing I'm not sure this means much. I figure my options are:

• Replace the HX hopefully at a lower price than the $1,800 listed on Catalina Direct. I did some searching for 302419 in the sources listed in the 101 topic but didn't find anything. I'll probably need to call around if I go the replacement route.
• Remove and repair the existing HX. Sounds like removal and inspection is something I should do every 2-3 years anyway and I doubt it would be difficult to drill out the zinc.
  
• The PO's yard installed the wrong size cutless bearing and at some point I want to upgrade to a SS propeller shaft, so I could just leave things "as is" until I have the boat hauled out for that.

Can anyone tell if this is the original heat exchanger?

Is it possible to guess if this EX is even worth repairing? I really want to limit the amount of time I'm not able to use the boat, but I don't want to damage the HX if it's repairable.

Thanks in advance for all your help!

[rmjohns]

Tom,
    I've had this happen to me as well. The end cap simply unscrews with that single bolt and then you can clean out the broken zinc.  There is a big rubber washer under the cap that you should be prepared to replace. I replaced mine the first time and then have reused it since then.   You should also be able to look in there and see if the little tubes look OK.  If you haven't had a overheating problem you're probably OK

Rob.

[Noah]

Check with Go2 Marine online:

https://www.go2marine.com/

Should find a SeaKamp replacement HX for $350-$500.

[KWKloeber]

That's the OEM Hx.

IIWMB I'd have a radiator shop inspect/pressure test it, and if ok, drill out the anode, boil it out, clean it up, and prime/repaint it.

Note that it has the OEM (brazed-on) brackets that can break loose.  Replacements have loose brackets that use t-bolt clamps to hold it onto the brackets.  So either have the shop make sure they are well-attached or remove them and change to the new type brackets.  A replacement Cu-Ni (I recommended for saltwater) Hx is about 500$ in round numbers.  Theres 3-4 different vendors of them.

Careful removing it as the bolts are probably corroded/seized into the bell housing.

[Ron Hill]

TVORG : Another source of HX parts is Glen Mar Marine  Tel 954-973-1260

A thought

[tvorgitch]

Great info! Now I know what that big rubber washer is for in the spare parts kit.

I'll try removing the end cap and then decide from there if I need to rebuild or replace.

This forum is amazing.

[waughoo]

Just as another data point, when I got my boat, I went through things one of which was this very zinc.  Like you, I removed the brass nut and the zinc didn't come with it.  Removing the end cap allowed me to get the remaining pieces out.  I also found bits of a past impellor that had made it through the tubes.  It's a good idea to look in there once and a while as part of maintenance.

[karista]

TVORG : Another source of HX parts is Glen Mar Marine  Tel 954-973-1260

A thought

Ron, FYI, Glen Mar Marine has been whole-sale only for several years. They were sold several years ago!

[Jon W]

Mr. Cool is another source. Make sure you check the types and orientations of the ins and outs very carefully. Some have straights and 90 deg elbows, some have straights and 45 deg elbows, some have combinations of all three. Descriptions alone can be misleading.

Can't zoom in enough to tell. Is the PN 302419 or 302413? Unless it's an assembly PN, it looks like it's the PN for the bracket not the HX. Got to love that it's directly over the transmission fill port!

[tvorgitch]

It's 302413, which must be the bracket as I can't find that PN for a heat exchanger.

It's just the angle of the photo that makes it look right over the transmission fill port. There is actually plenty of room to fill the transmission.

[Jon W]

As a starting point check the ins and outs of 302631CN which is a 3" copper nickle HX for ~$450 that comes with brackets. You'll need to figure out a modification for the missing piece the HX mounts to, or relocate the HX to under the aft berth. Good luck.

[KWKloeber]

Jon

Why do you say "missing"?

The M35 had 2 different Hx mounting methods.  The earlier serial numbers had a single bracket like the M25s that bolted horizontally to the top of the bell housing.  The difference was the M35 bracket is 3" and the M25 bracket was 2".

Late S/Ns had the two brazed-on brackets that bolt vertical to the face of the BH, like the XPs.  It appears that she is a late model and it boltz vertically to the BH. 
If he wants to he can change to the 2, separate "spoon" brackets (explained below.)

[Jon W]

Hi Ken. I wasn't able to zoom in on the photo with my computer. It looked like the bolt and tab of the right side HX bracket had been cut off. Using my phone I could zoom in and see what I thought was a cut line, is a shadow. The right side bolt and tab are there just hidden in the shadow. So no modification to figure out. Looks like the shadow is what I thought was the "nibbling" on the 302413 bracket as well. Good catch, thanks for asking.

[KWKloeber]

The part number (I haven't verified it) is for the bell housing, embossed on it below the Hx.

The p/n of the Hx is in the M35 parts manual on the wiki and is the number Seakamp (and others) would x-ref to.

[tvorgitch]

After removing the HX end cap, I was able to clean out the remnants of the zinc, but I still had to pick away with various to tools to clear the hole for the new zinc. I will check this more often from now on.

The 302413 number is not on the HX but on the bell housing. This must be the original HX as it has the welded on brackets and the one on the port side is loose. I did back flush the HX by removing a hose from the fresh water pump and using a mirror, the HX tubes looked to be in good shape, so I will probably remove it and have it cleaned up at a muffler shop when I have the boat out for the new shaft.

Thanks again for all the help.