How long can a diesel sit idle?

Jan 28, 2023
10
Hunter 41ac Merritt Island
We need to leave our boat for as much as eight months. Can we leave the diesel alone during that time? Or would it be worth paying someone to come in and run it for 10 minutes once a month? Same question for our Fisher panda generator. I’m interested in your opinions.
 

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
22,913
CAL 35 Cruiser #21 moored EVERETT WA
Check your Engine Manual for instructions on long term engine storage.
Yanmar for their 3JH4E offers this advice.
If the engine will not be used for an extended
period of time, special measures should be
taken to protect the cooling system, fuel
system and combustion chamber from
corrosion and the exterior from rusting.
The engine can normally stand idle for up to
6 months. If it remains unused for longer
than this, please contact your authorized
Yanmar marine dealer or distributor
 
Jan 4, 2006
7,218
Hunter 310 West Vancouver, B.C.
Or would it be worth paying someone to come in and run it for 10 minutes once a month?
Worst thing you can do for a diesel. The oil collects the water from the products of combustion and emulsifies. The emulsified water then sits in the bearings and does its thing which just happens to be corrosion. When the engine shuts down, the cool cylinder walls will be coated with water vapour depending on which portion of the cycle they last saw. If both valves to that cylinder are closed, not good. Every time you start your engine, you want to run it long enough and hard enough to get the oil up to temperature and drive the water out of the hot oil.

Keep in mind, the above is occurring on a microscopic scale each time the engine is run for 10 minutes and stopped. This practice does nothing to aid the engine so don't bother.

I always leave my engine to sit undisturbed from late October until late April. Starting up for the first time after a long shut down is where you want to exercise a bit of care. Pull the stop and crank the engine for about 5 - 10 seconds. Let the engine sit for a minute or two and repeat once more. Sit for a minute and everything should be good and wetted with oil. Start the engine.
 
Last edited:
Oct 6, 2007
1,123
Hunter H30 1982 Chicago IL
My boat is stored for winter, on the hard, for almost six months a year without issue. The engine is winterized: Oil & filters are changed (Always store a diesel engine with clean oil. The carbon in dirty oil is corrosive.) and the fuel tank gets a good dose of Biobor JF and Stabyl to protect the fuel along, plus a whole list of other climate appropriate steps. Running the engine for short periods may be the worst thing you can do. Look up the manufacture’s long term storage recommendations for your engine and generator.

I’ld almost be more concerned about the long term effects of humidity and condensation inside your boat. I store for the winter with a half dozen DampRid buckets in the cabin and they need to be checked, emptied and refreshed. I check the boat every four to six weeks during winter storage. It looks like you’re in Florida, which adds to my concern about humidity and condensation as well as storms. I don’t know what the best practices are for your climate. Hopefully others in your area will comment.

You absolutely need someone you trust regularly checking on your boat while you’re away.
 
Last edited:
Jan 28, 2023
10
Hunter 41ac Merritt Island
We’re addressing condensation by having a dehumidifier running on shore power, with battery and solar backup. It drains thru the galley sink. Only through hull open is that one. And we gave the boat a good hose test for leaks. And low-power fans running to keep air circulating past the dehumidifier.
Diesel tank has been treated with stabilizer and biocide, and left full.
 
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Likes: Dalliance
Feb 10, 2004
4,102
Hunter 40.5 Warwick, RI
My Volvo aux and Westerbeke genset sat for 18 months thanks to the governments actions regarding the Chinese virus. Both were winterized per normal with fresh oil. I cover my engines with towels to ward off condensation. I cover the air intake on the genset and stuff rags into the hull exhaust exits. When they were finally restarted, they both started instantly like they had been running the day before.
When I winterized, I didn't know it would be for more than one winter, so I did nothing special.

YMMV.
 
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Likes: JamesG161
Jan 7, 2011
5,489
Oday 322 East Chicago, IN
You don’t mention if the boat is being left in the water or on the hard. If out of the water, then similar to what @Dalliance said…

I store my boat on the hard for 6 months each winter…

Change the oil, make sure batteries are charged, then disconnect them. Make sure fuel tank is full to help keep condensation to a minimum in the tank. Make sure cockpit drains are open and clear. I can sleep easy all winter without worrying about the boat (much) :)

If the boat will be left in the water, that opens up a whole lot of issues. I would certainly have someone check on the boat frequently, but better to start the engine less frequently, but run it harder (tied to dock and in gear) to warm it up. Or have them take it for a 30 minute rider around the area. You can’t really disconnect batteries because you need your bilge pump operational. You should be checking water level in batteries if the are on a charger tat long…all kinds of issues when left in the water.

Don’t do what this owner did…



Greg
 

jviss

.
Feb 5, 2004
7,089
Tartan 3800 20 Westport, MA
We’re addressing condensation by having a dehumidifier running on shore power, with battery and solar backup. It drains thru the galley sink.
That doesn't address condensation inside the engine, and inside the fuel tank.
 
Jan 4, 2006
7,218
Hunter 310 West Vancouver, B.C.
That doesn't address condensation inside the engine, and inside the fuel tank.
He filled the fuel tank so minimal condensation there.

Diesel tank has been treated with stabilizer and biocide, and left full.
However, I'll bet he'll continue to run his engine for ten minutes and then shut it down while cool. Our marina is overrun by nut cases who insist on doing just that. I also notice that many of those same boats are also smokers, even when coming back from a long hot run in the summer.
 
Jan 4, 2006
7,218
Hunter 310 West Vancouver, B.C.
Philip Morris should use that as an advertisement :

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..................................... including long distance runners.
 
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Likes: JamesG161
Feb 10, 2004
4,102
Hunter 40.5 Warwick, RI
We’re addressing condensation by having a dehumidifier running on shore power, with battery and solar backup. It drains thru the galley sink. Only through hull open is that one. And we gave the boat a good hose test for leaks. And low-power fans running to keep air circulating past the dehumidifier.
Diesel tank has been treated with stabilizer and biocide, and left full.
Be aware that dehumidifiers don't work at temperatures much below 50 degrees. I use buckets with colanders and put a couple cups of calcium chloride in the colanders. The salt absorbs the moisture in the air and it drops into the bucket. Seven buckets yield just over a gallon of water in the spring.
It is also a power-free solution.
 
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Likes: jviss
Nov 6, 2017
78
Catalina 30 5611 Stratford, Ct
Two things can happen. The batteries can go dead and the diesel tank can get moisture in it. You should before long-term storage run the engine until it reaches operating temperature and change the engine oil and filter. If it is stored in a cold location winterize the engine as normal. The batteries should be removed and maintained at a normal charging rate. Some say to fill the fuel tank but that is not going to help with moisture in the fuel as any air space in the tank will cause condensation. You should also understand that the only source of moisture that enters the tank is from the tank vent. The amount of which is very small and is simply removed with a water separator type filter. There are many myths when it comes to boats. You might be surprised at the amount that are simply not true. Or you could disconnect the batteries (negative cable only) and come back after 8 months connect the cables and be on your way.
 
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Likes: jssailem
Jan 4, 2006
7,218
Hunter 310 West Vancouver, B.C.
There are many myths when it comes to boats.
Agreed. I'd say more than most things in life. You got almost 100% on your write up :clap:.

The batteries should be removed and maintained at a normal charging rate.
Batteries at 100% SOC are good to much lower temperatures than normally encountered. Better idea is to leave them on the boat and save your back. But just as bad for your boat ..............................

Or you could disconnect the batteries
........................................... but not so good for the bilge pump.
 
  • Helpful
Likes: JamesG161
Jun 1, 2009
1,824
Hunter 49 toronto
Old saying ….
What rests ,,, rusts.

You definitely want the FP started from time to time. After just a winter layup, mine groans to me the first time I press the button (while crossing my fingers )