Diesel Motor Crash Course

If you are growing weary of all our technical dramas starting out with “it all started out so simply”, then just imagine our frustration.  This one really did come out of nowhere, or to be more precise, from the cautionary tales of a fellow mariner who had a nasty surprise during his recent summer sailing trip.

Guru Bob, recently returned from the aforementioned trip, suggested that we check the pre-filter of our diesel engine to look for any rust particles that may be emanating from our 20-year-old “stainless steel” fuel tank that just might clog up a fuel line when you least expect it.  Since the fuel is of dubious origin (the Caribbean) and had been sitting in plastic jerry cans for over a year before being put in the tank, he also suggested we check for condensation.

Water pump impeller and gasket.

The engine has always been an element of moderate anxiety for us, and we were eager to get to know it a bit better before trusting it blindly in potentially dangerous situations.  Before tackling the fuel lines, we decided to start with something simple: checking the water pump impeller and gasket.  When we saw that it was, in fact, a simple operation, and that the impeller was in good condition, we should have suspected that fate was just teasing us.

Pre-filter before cleaning, the contents, and the cleaned canister.

Bolstered by this initial success, we moved on to the pre-filter and water separater.  By turning a small valve at the bottom of the filter canister, you can bleed out a sample of the fuel.  Ours looked like Turkish coffee.  Guru Bob explained that it wasn’t supposed to look like Turkish coffee.  We took the filter apart and, not surprisingly, it looked like the bottom of a Turkish coffee pot.  The liquid drained from the canister, however, took on the allure of a nice Black-and-Tan mixed beer, with the water and dark matter in the bottom and the diesel floating on top.  Cleaning it out and replacing the filter was a relatively straightforward affair, but of course, this was a sign that there was trouble brewing further along the line.   

The filter, before and after.

Next, we decided that we should check out the fuel filter.  Not surprisingly, it looked like a Turkish coffee pot, too.  And once more, cleaning out the filter canister and replacing the filter was easy*, but this was just a symptom of bigger problems yet to be resolved.

(* “easy” is a relative term meaning that it is conceptually simple.  However, even the simplest task on a boat motor is a royal pain in the butt because space is limited and access to the part you want to work on is always blocked by at least two other things.) 

Tank goobers.

Examining the root of the problem could no longer be avoided, and we decided to inspect the tank directly by removing the fuel gauge sensor and peering into its fitting hole.  The good news is that there was no rust.  But there were numerous black gelatinous goobers floating in the fuel and clinging to the bottom, indicating a bacterial bloom.  

 The solution: 

• Drain the tank.  (Guru Bob had a kick-ass electrical drill-driven pump)
• Remove the tank from the locker.  (Dehler calculated this to the ½ milimeter and it was not easy to get it in or out of the locker…lost a little gelcoat around the rims.)
• Clean it with a hot water high-pressure hose.  (That part was fun.)
• Rinse it with gasoline and let it dry.  
• Put it back into the locker and reconnect all the lines.
• Filter the diesel and treat it with an anti-bacterial additive.
• Put the cleaned diesel back in the tank, and
• Prime the system to get the air out.

Tank operations.

This all took two days.  The shipyard mechanic came to help us prime the system once we had got everything put back together.  There is a small hand pump on the motor between the pre-filter and the filter.  You remove a screw to open up a hole on the top of the filter to let the air escape while you pump.  We’re glad the mechanic was there, because it took a helluva long time to prime and we would have given up thinking we were doing something wrong.  But we eventually got the big belch and the fuel ran clear.

Motor running smoothly ... with no leaks !

The mechanic then turned to us and said, “I think it would be a good idea if we fired up the motor to make sure everything is running smoothly before you put it in the water.”  YES !!  We weren’t sure how to manage this ourselves and having him there to help was a great relief.  We rerouted the water intake to a bucket that we filled continuously with a hose, and with little effort, the motor started right up … and NO LEAKS !!  What a great compensation for 2 full days of really dirty work ! 

While the mechanic was still with us, Patrick brought up a recent story we’d read in the newspaper about a sailboat who’s engine began revving out of control, overheated, burned and sank the boat in a matter of minutes.  The captain had shut off the diesel to the motor, but that had no effect.  The mechanic explained that this can happen when the oil is too full, and that the only thing to do in that case is to smother the engine by blocking the air intake.  He showed us how to do this by opening up the canister of the air filter and placing a rag in the intake pipe.  But when he did this, we discovered that there was no air filter.  The wire basket that holds the filter was there, but the thin foam filter was missing.  That one truly was easy to fix, but very expensive for such a flimsy little thing.

I’m sure that the care and feeding of the marine diesel motor still holds many mysteries for us, but we certainly feel more confident after our 2 day crash course and we know that everything is now in good working order.  With only 5 days left on land (in theory) it’s great to get this out of the way.