Small heat exchanger issue

[Porchhound]

Boneheaded not to have checked the heat exchanger zinc on new boat before leaving for the winter. What zinc? All eaten away with corrosion visible on outside of the plug plus NO WATER came out of exchanger when I pulled the 7/16 plug. We ran her from Olympia to Port Orchard last November with no temp issues. I know the zinc is a problem, but is it normal for the heat exchanger to be dry?

[KWKloeber]

Complete information please? Are you on the hard and this is the first time you've looked at the heat exchanger? Have you run the engine in the water? Please give us complete information so we can help you.

[Porchhound]

In the water. I ran the boat for eight hours changing marinas here in the PNW last Fall before I left. I did not inspect the exchanger when I bought the boat last November. There were no temp issues on the eight hour run.

[KWKloeber]

Did you winterize after running the engine or is it now exactly as it was after the run to the new marina?

[Porchhound]

I didn't winterize the engine.

[Porchhound]

The PO only put 30 hours on her in three years and didn't change/check anything. There is no telling how long the zinc has been gone...which is why it was boneheaded for me not to check it. New boat owner ignorance is my best excuse.

[KWKloeber]

Not having a anode isn't fatal over the short term - there's more critical things that can ruin a day.

if you didn't winterize there should be seawater left in the Hx, unless:

- You don't have a high vented loop and the Hx drained downhill into the muffler.
- The seawater impeller was removed or replaced, or the pump cover opened, which would drain the HX.
- One of the end caps is leaking.
- The Hx somehow siphoned into the muffler - when was the vented loop (if there is one) last serviced?

I don't see how the Hx could siphon the other direction with the thru hull valve closed.

[Porchhound]

Ex cleaned out, new zinc 3/2019-- 45 hrs on engine since. There its a loop coming out the top of the exchanger. The zinc plug looked to be leaking based on a better inspection of that area, as is a hose on the starboard bottom of the Ex. I'm looking for a description of that system so I understand all these connections and the flow better. Thanks for your help!

[Ron Hill]

Porch : You failed to mention your Hull #, production year and engine!!  Looks like you may have the M25 engine with the 2" heat Exchanger???  if so you probably have a 1986 C34??

It's hard for me to understand how you just jumped intp that boat and took off on a trip with out even looking at the Impeller?  I assume that you looked at the oil and fuel levels??  Then left it without winterizing the engine, water heater, head and fresh water system??

You've got a bunch of things to check!  Ken's mentioned JUST a few!!

A few thoughts

[KWKloeber]

Kudos for wanting to learn about the engine. Download the ops manual for the m25 -25xp etc. that's on the Wiki sit under "Manuals"
It has the diagram, which I corrected and is inserted to replace the incorrect diagram.

UNFORTUNATELY the link on the Tech Wiki home page to the Manuals is broken - I've been frustrated trying to get it fixed for like 2 years now - which must fall on deaf ears. The C34 powers' answer is to search for "Manuals" once on the wiki site.

I presume that she has an M25-xp? (It would be helpful to put complete boat/engine info on the side panel (profile) or signature.)

Ken K

[Porchhound]

I checked the oil, fuel, and coolant before I left Olympia and winterized the head and fresh water system when I arrived here. I had three spare impellers, spare filters, etc before I left. Some on here advised against a more thorough winterizing due to constant water temp way above freezing and a boat heater in operation. What I didn't check was the engine system zinc. All systems have been checked this year with the only issue being a plug on the raritan leaking. I also replaced the bilge pump and float and will be replacing the battery charger which I think was responsible for cooking the PO's house bank. I'm working through the engine system now before I take her out.

You are correct on the engine model and year and I changed my profile to reflect that info.

[KWKloeber]

2" heat Exchanger???  if so you probably have a

M25xp!?! MEA CULPA!  I "miss-inspected" the photo and didn't even notice the 2".

You likely don't need the 3" Hx where you are but note that with 37 years on her in salt, you are overdue to discover a pinhole leak between the seawater and closed coolant sides of the Hx. In freshwater mine went around 20 years. 

There's a chance — that might have emptied your Hx as the engine cooled and the vacuum created sucked seawater into the closed system. If the pinhole is in a spot like a tube on the bottom that's covered with seawater until nearly empty, the closed system could suck out the Hx until the pinhole is exposed to air (breaks the vacuum.) 

A leak in the Hx will manifest itself as an unexplainable/undetectable loss of engine coolant with no hose leak or blowby into coolant recovery tank (if she has one) seen.  The ~15 psi in the closed system when the engine is hot pushes coolant thru the pinhole, to the Hx seawater side, to the vented loop, to the muffler, out the exhaust.  One might detect the sweet odor of coolant in the exhaust.

[Porchhound]

Thanks. I'm going to replace the zinc, start the engine and lay in the aft berth looking for leaks.

[KWKloeber]

Wrap a strip of paper towel around any suspect fittings/hoses.

[Noah]

FREE TIP: I use the blue Scott Shop (paper) Towels. More expensive but much easier to see drips when towel gets wet. Also stronger.