What To Do With The Diesel?

After trying many solutions, our current solution is to fresh water flush our diesel and shut it down entirely while we’re gone.  This solution isn’t necessarily recommended by all diesel mechanics but the logic appealed to us … no carbon build-up from running the diesel while not under load, fresh water flushs out all the sodium and sea salt buildup from the prior six months plus … we’re big subscribers to Eileen Quinn’s song lyric …”If it ain’t broke DON’T USE IT!!!   🙂

We’ve tried many different ways to deal with the diesel while we’re gone for six months.  We started by having our caretaker start the diesel and let it run for a few minutes a few times a month.  But this added wear and tear to our over 25 year old diesel.  Plus diesels don’t benefit from running while not under load – they build up carbon and bad things can happen.

We first heard of fresh water flushing our trusty 1985 vintage Nanni Kubota 4 cyl 30 hp diesel while we were cruising in Panama.  Yikes!  The idea of NOT having a caretaker start and run our diesel engine once a week while we were gone for six months terrified us!  What happens if we try this new idea and the diesel locks up never to start again while we’re in somewhere in paradise.  The idea of our trusty diesel non-functional is NOT something I want to think about!

The concept is the same as we always use with our Tohatsu 8 hp outboard — flush enough fresh water though it and shut it down.  It’ll work perfectly when we return months later… or at least the outboard always has … yeah right.

So we tried it.   We returned six months later, opened the seacock and with trepidation turned the key to warm up the glow plugs before taking the plunge to turn to start.     First the diesel rumbles … OK, maybe it’s ticked because we left it alone for six months … maybe it’ll get over it & start … or maybe not.   WAIT — IT STARTED!!!  WOOHOOO!!!!   That’s got to be the best feeling in the world.

When we return to the boat, we expect to have a growing list of things that DON’T work because they haven’t been used in six months … it’s a fact of life while commuter cruising … but this one is a WINNER!!!   Four years running, it hasn’t failed us yet… maybe I shouldn’t say that, I’ll jinx myself for Fall 2011 …. knock on teak!!!

Here’s the process:

1.  Close the seacock so the salt water cannot come in.

2. Put a fresh water hose in where the intake is … our boat has a strainer sitting there – see photo.  We take the top off, pull out our strainer and stick the hose in.   I turn on the hose and David crimps it bending the hose to keep water from flooding the quarterberth since that’s the access point to the intake.

3.  I start the diesel and he lets the fresh water run through it – circumventing the salt water cooling water with fresh water.  I check to make sure we have water coming out of the exhaust.   Everything looks good, so we let it run for 5 minutes or more with fresh water, hopefully rinsing all the saltwater and associated crap out of our diesel.

4.  Shut down the diesel.  Shut off the water.

Before we leave the boat, we put a piece of blue tape across the ignition switch saying “STOP!!!  DO NOT START! ENGINE SEACOCK CLOSED!”.  We also leave emergency starting instructions on our caretaker’s list … just in case!




  1. Perhaps it was just me but when I saw the title “What to do with the Diesel” and further read “fresh water flush our diesel and shut it down entirely while we’re gone.” I was shocked and confused because I was thinking that the author was proposing a remedy to the issue of Old/Contaminated/sludgy/biologically infected Diesel Fuel which often causes clogged fuel filters, injectors etc, after sitting in your tanks and lines for months with the boat laid up but apparently this tip appertains to flushing the engines cooling system and has nothing to do with Diesel Fuel.

    Surely flushing your Diesel fuel lines with freshwater would probably not be recommended, so hopefully everyone reading this article will have understood the article better than I and not put the running garden hose into your fuel tanks and run your engine until it dies.

    • Hi Jim! Thanks for reading Commuter Cruiser! Your comments are appreciated and obviously I screwed up writing the fresh water flush the diesel post significantly! We’re just flushing the salt water out of the salt water cooling system – nowhere near the diesel fuel – heaven forbid! Here’s the same process on our old Tohatsu 8 HP outboard that maybe explains the general process and the why better. I apologize for any confusion! http://commutercruiser.com/how-to-fresh-water-flush-outboard/ Cheers! Jan

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