Tips on Yanmar Diesel Engine Maintenance

It is about 2 years ago that Brian Aiken, Tom Winlow and the author undertook a pilgrimage to E&C Marine in Toronto to be educated in the fine art of sailboat small diesel maintenance. Basically what Charlie of E&C taught us was : change your oil and fuel filters on a regular basis, keep your fuel clean and you will be fine. If you are really brave, you can adjust valve clearance and do engine alignment, but anything related to injectors and fuel injection pump is best left to the experts.

As you may know Whiskeydream has been south as far as the Turks and Caicos this winter and had to deal with engine problems as early as north in the Chesapeake bay and as a result I got to pick the brains of more diesel guru’s than I had intended. I also had the privilege of attending a diesel maintenance seminar by Larry Berlin of Mackboring, the main NE-USA importer of Yanmar, during the Annapolis boat show. Larry  has spent his entire career of more than 30 years working with Yanmars, so he can tell a few entertaining stories about not so bright sailboat owners.

So this article came about as the combined result of notes from Larry’s seminar and my unplanned visits to diesel gurus during my trip. It applies directly to the 2GM20F Yanmar, but probably is also useful in the maintenance of other diesel engines.

1. Engine Oil

Use only major brand name oil with a diesel classification of at least CE,CF,CG or higher. The discount stuff you can buy in department stores is definitely inferior and the few dollars extra you pay for a major brand name are worth it to ensure adequate lubrication.

Although the oil dipstick shows a min and max level, it is very important that the oil level be maintained very closely to the max mark. This has to do with the  fact that the oil level in the crankcase is high enough that the crankshaft and connecting rods will splash oil around . This lubrication of the lower moving engine parts by splashing is as important as the oil that is applied by the oil pump to the upper parts of the engine.

2. Oil Filters

Use only genuine Yanmar oil filters. After market filters by Sierra and others can lead to oil leak problems.

3. Coolant

Mackboring insists that you use what is called Extended Life Coolant. Its main chemical component is Ethylene Glycol and it is easily recognized by a pinkish colour. The green stuff that is widely used in automobiles can cause premature corrosion in the aluminum and brass parts of the cooling system. Approved products are Texaco Long Life (PC 7997 and 7998), Havoline Extended Life (PC 7994) , Dexcool Long Life ( GM Dealers) and Prestone Extended Life (PC AF888).

When you change from green to pink, it is important that all the old green coolant be flushed out as the two don’t mix. Makes for a lovely job on a rainy day.

4. Failure to start

If the engine does not start on the first 5 seconds of cranking, STOP and do not keep trying. Diesels start immediately or never! First of all shut off the seawater intake valve as continued cranking will eventually fill the exhaust mixing elbow with seawater. If this happens, water can enter the cylinder through the exhaust valve and the starter motor has enough power to destroy the engine as water is not compressible.

After the seawater supply is shut off, find the cause of the starting problem which is usually fuel related, i.e. bleed the fuel system, check for contaminated fuel or plugged fuel filters. Once the engine sputters to life, you will have plenty of time to open the seawater valve. I admit to having forgotten that I shut the seawater valve and it takes at least 5 minutes at idle speed before the HiTemp alarm comes on, without obvious harm to the engine.

5. Carbon buildup

The typical diesel engine usage by a sailboat owner is about the worst you can ask for. By typical I mean start her up, take her out to the first buoy, raise the sails and shut off that noisemaker. Same procedure in reverse on the way home. Also many hours of battery charging at medium speed and practically no load by a cruising sailor is hard on the engine. The Yanmar GM series engines are classified as a hi-revving, high compression engine. The max RPM is 3500 and the long term RPM is 3000. The bottom line is that the typical sailboat owner abuses the engine, which leads to carbon buildup in the cylinders, injectors and mixing elbow. In other words the diesel engine is happiest at high rpm under high load.

What is the poor sailor to do? First of all, warm up the engine at least 10 minutes at the dock before leaving. Once under way, run her fast for as long as possible. Fast means 2500-3000 rpm. This will to some extent reduce carbon buildup. Unlike gasoline engines, you cannot blow out carbon buildup by extended hi-revving of the engine. Similarly once the engine is nice and hot, you need to idle her for 5-10 minutes so she can cool off before shutting her down. If for whatever reason you came chugging home at 1700 rpm, rev her up to 3000 rpm for a minute or so before going to idle for the cooldown period.

If there is carbon buildup, it will be evident by rough idling. Take your injectors out and have them tested for spray pattern and injection pressure by a diesel shop. New injection nozzles are not as expensive as you think (about USD $60 each). The Yanmar manual also recommends inspecting the mixing elbow for carbon buildup every 300 hours. Just pull the exhaust tube off and look inside with a shaving mirror and flashlight. If the passage is more than 30% blocked, you need to remove the elbow and chip the carbon  out with a screwdriver or old chisel.

In my case I also got carbon buildup as a result of timing misalignment. The misalignment was caused by at least 2 “diesel gurus”, who re-installed the injection pump after pulling the gear case cover . Injection timing is controlled by brass shims between the pump and the gear case cover. INSIST on a timing check every time the injection pump is re-installed.

6. Prop stop under sail

A lot of sailors hate the noise from the free spinning prop when under sail. It can be stopped by putting the transmission in gear. If you do so, make sure you put it in reverse gear. I forgot the exact reason, but guru Larry said you can damage the transmission if you use the forward gear to stop the prop.

7. Engine stop cable

For reasons only known to Yanmar, the engine stop cable is not made from Stainless Steel and can rust ferociously especially in salt environment.  To control the rust, disconnect the cable at the engine side, straighten out any kinks from the setting screw and pull out the cable in the cockpit as far as you can see rust development. Remove rust with emery cloth and rust remover like T9 and then generously coat with waterresistant grease. Then reinstall the cable again. Make sure the engine stop lever is in the full “run” position, when the stop cable is pushed in all the way. I had to do this once a month in the salt environment of the Bahamas and ICW.

8. Engine alignment

Check your engine alignment at least once a season. To do this, remove the 4 bolts that hold the 2 transmission and engine shaft flanges together. Push the 2 flanges together and it should not be possible to insert a 0.004” feeler gauge anywhere between the 2 flanges. If you can, you need the adjust the engine mount bolts/nuts until you are in spec. Make sure your boat is in the water and the mast is installed and tensioned to spec when you do all this.

In my case I suffered incredible humiliation by an apprentice guru, who in 5 seconds pointed out a loose mounting nut after my complaint of excessive engine vibration. Engine misalignment does not only cause vibration. It can also destroy your transmission and stuffing box in very short time.

That is all I can think of for now. These notes were composed in beautiful Hopetown Harbour, Abacos, Bahamas under sunny skies, so don’t feel too sorry for all the engine frustrations Whiskeydream encountered in its winter journey.

George de Witte