Yanmar 1GM10 RPM / fuel

I would like to share some experience with the Yanmar 1GM10 diesel engine. Since I’ve been sailing a Westsail 32 engineless for over four years now, coming into a boat like the FC (#27) with a Yanmar 1GM10 opened up the shallow bays along the Gulf of Mexico I could never reach in the previous boat. Mind you, I know nothing about diesel engines!

Our first real use of the engine was in 4 foot following waves and 20 kt winds for 10 nm. The tank was 1/2 full (28 gallon Costa Mesa CA SS below engine). RPM 2800 maximum, with occasional drop to 2000.

I topped the tank off with new fuel - adding about 15 gallons.

The next real use was in similar conditions, with similar performance.

The next outing we completed a 35 nm sail in calm to moderate conditions and started the engine for lack of wind. RPM 2600 for perhaps 3 nm. Stalled. It woudl restart after sitting for 10 minutes but stall again after 15 minutes. RPM 900.

I changed a fouled fuel filter and it now runs like before, RPM 2800.

I changed the oil, using T6 synthetic. I added StarTron fuel treatment.

A few outings, RPM 2600 under load but no stalling.

I bought a laser tachometer, measuring the RPM against the tachometer. The tachometer reads low. RPM 3700 no load. Tachometer reads 3500. RPM 2600 under load. 6" propeller and prop shaft turns freely by hand.

I thought this was as good as it was going to get and I was pleased anyway and enjoying the little engine.

Next, wanting to calculate cruising range with 28 gallons, and wanting to burn out all the old fuel, tied her to the dock and ran the engine full throttle under load. She ran for 50 hours straight. > 300 nm @ 5kts estimated range full tank.

I put a wooden rod into the filler port and found an oily brown residue with 1/4" fuel. I checked the fuel filter - spotless and like new.

I put in 5 gallons new diesel, added Startron.

Engine starts instantly, and now by hand using the crank and decompression lever, and without batteries.

RPM under cruising load 3200 (not tied to a dock) with less than 5 gallons fuel after 20 nm sail in 5 to 30kt wind 2 foot seas. Still starts by hand and intantly. Fuel filter remains clean.

I’ve had opportunities to visit with several diesel experts. The comment that sticks was “Sounds like you cleaned out your injector with the 50 hour run and Startron.” I am of the mind if there is no water/fuel interface for organic growth, there will be no growth at all, so I am hoping the sludge will eventually burn out. This option is much better than a new fuel tank, tank washing or fuel polishing in my opinion.

You might be surprised how much algae is in your tank. Fuel polishing is cheap and highly effective. :slight_smile: id love to see some pictures of that boat :slight_smile:

Hey Patrick. Thanks for the report. I’ve messed around just a couple times hand cranking my Yanmar and after a few tries I decide I’ll figure it out later. Which will likely mean when it’s absolutely necessary.So I should figure it out sooner. Could you tell me your procedure? Thanks.

The engine does not need batteries to run, and for some reason this was a pleasent suprise to me. I imagine a time when my batteries are not available and would still like to run the engine.


Describes the process with pictures.

Remove the table over the engine house because you need access to the decompression knob and crank at the same time. Kneel port side, facing starboard, right hand on the decompression lever, left hand on the crank.

  1. Disengage the transmission - “pull out the warm up knob”
  2. Place throttle in full speed position.
  3. Raise the decompression lever with one hand - for me, my right hand, while placing my body 90 degrees to the crankshaft, and placing my left hand on the crank.
  4. Crank hard, 5 revolutions minimum to gain momentum.
  5. Release the decompression lever and crank harder not letting up on muscle power.
    6 Crank 3 revolutions, engine will start and crank will disengage.

I hate to hijack this thread but would love to hear your opinions and reasons for downsizing to such a small boat as most of us move in the opposite direction.
PS Congrats on acquiring the best boat ever designed or built :slight_smile:

Hey Patrick. It took me a couple tries to get the technique and my body in the right location and then she started right up. I feel much more prepared in case I run my batteries down. Thanks.