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Maintenance

EP47 - Trying to save the heat exchangers from our aging Yanmar engines | Part 1

Can we save the aging heat exchangers on our Yanmar engines — or are we risking catastrophic failure? In Part 1, we fight corrosion and weigh repair vs replacement.

Shawn Hammer

— 2 min read

Episode Overview

Marine diesel engines don’t usually fail dramatically. They fail slowly — internally — when cooling systems stop doing their job.

In this episode, we turn our attention to the heat exchangers on our aging Yanmar engines. Replacing them outright would be expensive. But running compromised heat exchangers risks something far worse: overheating and long-term engine damage.

So the question becomes:

Do we try to save them?
Or do we walk away and order new ones?

This is Part 1 of figuring that out.

📺 Watch Episode 47 👉

Yanmar heat exchanger removal and inspection during sailboat engine refit

Why Heat Exchangers Matter

On a marine diesel, the heat exchanger is the boundary between raw (salt) water and engine coolant. It’s what allows the engine to stay at operating temperature without mixing saltwater into places it absolutely doesn’t belong.

When they clog, corrode, or leak internally, the consequences can range from:

  • Reduced cooling efficiency
  • Elevated engine temps
  • Oil contamination
  • Complete engine failure

Replacing them is straightforward — but expensive.

Rehabilitating them? That’s another story.

Getting Them Apart (The Hard Way)

Before we could even evaluate whether the exchangers were salvageable, we had to get them apart.

And that turned out to be a project in itself.

Years of salt exposure and internal corrosion made simple fasteners anything but simple. What should have been routine disassembly became careful persuasion, patience, and a lot of second-guessing.

Every bolt raised the same question:

Are we fixing this — or just proving it’s too far gone?

The Real Question: Repair vs Replace

There’s a constant tension in refit work:

  • Spend money now.
  • Or spend time now.

New heat exchangers would eliminate uncertainty.

But if these can be cleaned, pressure tested, and restored to full flow, we preserve budget for other critical systems.

The risk?

If we guess wrong, we could destroy an engine that still has thousands of hours left in it.

That’s the calculation.

How This Fits Into the Engine Series

This episode continues our deep dive into bringing our Yanmar engines back to reliable condition.

If you’re following the full maintenance arc, start here:

EP47 marks the point where we stop cleaning and start making hard decisions.

What Comes Next

In Part 2, we’ll determine:

  • Whether internal corrosion has gone too far
  • If flow can be restored safely
  • And whether these exchangers go back on the engines — or into the scrap pile

When you’re maintaining your own diesel engines, every decision carries weight.

This one might carry thousands of dollars.

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