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Heat Exchangers A Closer Look

Maine Sail

Member III
When we bought this boat two years ago one of the things on my list was to remove and clean the heat exchanger (HX from here on). Now that my bell housing is cracked :mad: I had a good opportunity to attack this and take photos of the process.

HX's are one of those things that many boaters find mysterious but they are in fact quite simple and easy to work on, especially the cylindrical type as used on Universal and Westerbeke engines.

A marine HX is very much like a cars radiator. Rather than cooling the engine antifreeze with air passing across aluminum fins, the marine HX uses raw ocean or lake water run through copper tubes. This raw water is doing, and serving, the same purpose as the air does on an auto radiator.

This is the basic anatomy of a HX. There are two sealed water loops or circuits in this tube, a fresh water side (engine antifreeze), and a raw water side (lake or ocean water):
107682452.jpg


To see inside simply remove this bolt and pull the cover plate off (this can usually be done on board if you have access and a closed seacock):
107682459.jpg


What's behind the cover plate? On this type of HX all that's there is an o-ring and rubber gasket. Be sure to have new replacements on hand before removal:
107682462.jpg


This is the most confusing part trust me! The in-coming raw water passes into quadrant #1 and makes pass #1. When it hits the end of the tube it makes a 180 degree turn and comes back for pass #2. It then hits the end of the tube again and is forced back though the HX for pass #3 where this process happens again and the raw water is finally sent out of the HX and into the wet exhaust system. In essence the raw water passes through four quadrants or quarters of the HX before leaving the HX. If you look closely you can see some eel grass and an old impeller vane. This first pass only consists of a few small diameter copper tubes so it's important to monitor temp and on an abnormal rise to use a good trouble shooting methodology and make sure it's not a blocked HX.:
107682465.jpg


This is the end I call the trouble end and it is the one I clean most often, thought eh other end can be bad too. With Universal/Westerbeke HX's the pencil zinc is almost the same width as the threads for the head. Zincs do funny things when they sacrifice themselves one of them being that they begin to flake and appear to get bigger in diameter. If the zincs are not changed often enough a few things can happen as did here.

#1 the zinc gets thin and the water pressure snaps it off the head where it remains until you remove the cap and clean it out.

#2 The zinc deteriorates, crumbles and flakes off inside the HX which can lead to plugged tubes.

#3 The zinc gets too fat and when you un-thread it the pencil zinc snaps off the head. People often assume the zinc was totally eaten but more often than not it just broke off because it went too long before being changed.

The zinc in the photo, which came out in one piece, was about eight weeks old. I change them about once every 8 weeks. The PO spent time cruising and was in many different areas, with different water/electrolysis issues, so getting to know his zinc schedule was probably tough, hence the crud. I should have pulled the cap a long time ago but my temps were running spot on. If you don't get a full zinc out it's a good idea to pull the cap and retrieve the pieces.:

107682802.jpg


I droped it off at the radiator shop for a cleaning then I clean it up and will paint it. I learned a long time ago that paying the $20.00-$30.00 (now $35.00-45.00) for an HX cleaning is soooooo worth it. Hell I can barely even buy the Rydlyme, to DIY, for what my local radiator shop charges.

When I got my HX back from the radiator shop it looked great inside, especially for 2800 hours, and pressure tested fine. The Dex-Cool must go though!

Here are a few photos to illustrate why keeping the zincs fresh is imperative. It illustrates just how many dissimilar metals are in a common HX for many diesel engines especially Westerbeke & Universal.

End Cap Before Cleaning:
108120805.jpg

This is Dezincification of The Brass End Cap (yes they are brass NOT bronze):
108122498.jpg


Ok so how many dissimilar metals can they fit onto one heat exchanger? We have copper, brass, bronze, solder and of course stainless bolts to hold the end caps on. That is five different metals!! Change your zincs!!

108177589.jpg

All clean and ready for paint:
108120808.jpg
 

JMCronan

Member II
Glad you were able to correct your overheating issue. I wasn't so lucky. My coolant kept disappearing, I finally checked the heat exchanger- bingo! The fresh water was mixing with the raw water and being shot overboard, i.e.- new heat exchanger. Changing zincs is much cheaper than changing heat exchangers.
 

Maine Sail

Member III
Actually..

Actually I did not have any over heating and the HX was surprisingly clean. The bell housing on my motor cracked so it was more of a "while you're in there" sort of thing. I am doing all kinds of preventative work while I have it apart.

Rear main seal, HX, rebuilt the starter, all new hoses for the engine, new PSS shaft seal, new motor mounts, new damper plate and retaining bolts. All wear items that are easier to do while I have it apart.

This is what led to the above work..
107573211.jpg
 

Dan Callen

Contributing Member III
Heat Exchanger

I have a zinc that the hex head has broken off leaving the remainder still flush with the threads and no common way to screw it out. How is the best way to remove the stud....might have to take it to a machine shop for removal or is there an easier way. Dan Callen Ericson 32-3 Andiamo
 

Maine Sail

Member III
Use..

Use a center punch and tap the center of the broken zinc head. The drill the center, it's brass so it should be fairly easy, the use an EZ Out to remove the head.

P.S. Soak it in PB Blaster first and remove the HX as itwill be much easier to work on..
 

Steve

Member III
Excellent Reminder--

My HX was a mess with flaked and crumbled zinc accumulation when we first acquired the boat in 1999. It's rather common but also over looked, we now pull those end caps each spring and flush out when we change out the zinc.

I once heard a conversation by a yard mechanic to thier customer saying he should change out, for new, his HX every other year to help ensure trouble free service... and of course they would be happy to accommodate this activity. Yikes.. run for hills, but I think many a no touch sailor get talked into these sort of things..

Steve
 
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