My father is a marine engineer and shipwright of many years experience and serviced my engine the first few years of having the boat before he encouraged me to have a go myself. Being a man of poor memory and many excel spreadsheets and much documentation, I made sure I created notes around the process. Below is a walkthrough of the service of our reliable and hardy Yanmar 2GM20. Note, this comes with no warranty and is based on my likely flawed scribblings.
For parts and spares, I always use the epic French Marine over in Brightlingsea who have cracking customer service and a great stock of both parts and knowledge.
Click below to download the workshop manual for the 2GM20 (and indeed all GM and HM engines), which includes the correct torque settings for all the bolts.
- Socket set
- Oil Filter remover
- Watering can
- Oil 2 Litres 15/40 (Mineral oil of API CI-4 or API CF4 standard), see here for an interesting write up. I use Shell Rimula (as did my father who was a marine engineer and a shipwright).
- PELA type oil sump pump
- Oil jug for pouring
- Fuel Filter and O ring
- C Spanner
- Oil filter
- 2 X Engine Anodes
Steps to winterise
- Remove oil using the sump pump. Put the hose of the sump pump down the well where the dip stick comes out from (quite fiddly indeed) on the stb side of the engine.
- Place a tray and lots (and I mean lots!) of paper-towel under the oil filter on the port side of the engine. Replace the Oil Filter using the Oil Filter remover. Smear the seal on the new oil filter with oil from the old filter, then put the new oil filter on as tightly as can be achieved BY HAND.
- Fill with the 2 Litres of Oil, check the dip stick. It should be slightly over filled as it has to refill the oil filter once the engine runs.
Run Antifreeze through the engine to protect it from freezing
- Make sure the engine sea cocks are off.
- Take the top off of the water strainer.
- Steadily pour a mix of 50% antifreeze and 50% water into the top of the strainer whilst running the engine until antifreeze comes out of the exhaust. This will only be a few minutes. It helps to have two of you do this, one in the cockpit to start and run the engine, then shut it off, and one down below doing the pouring!
- Turn off fuel if fuel valve present.
- Drop the engine fuel filter body off with C Spanner.
- Take the filter out of its casing, being careful to catch any diesel that will escape as you extract the filter from the housing. You may need to pry the filter out with a screwdriver delicately to get it out.
- Gently push the new fuel filter into place.
- Reattach the fuel filter housing.
- Turn on fuel if fuel valve present.
- Slacken the bleed screw at the top of the fuel filter.
- Pump the fuel pump on the Stb side of the engine behind the fuel filter until fuel comes out of the bleed screw. This is quite hard to find, and requires quite a few pushes (and make sure you push it far enough else it will not draw the fuel!).
- Slacken the injection pump bleed screw.
- Pump some more until the fuel comes out of this bleed screw too. Tighten strait away to disallow fuel to drain away.
Impeller removal (to stop it setting in shape over winter)
- Remove the two bolts holding the water pump pully on.
- Remove screws on the back of the casing and remove the impeller (put a screwdriver either side and lever it out gently, making sure not to damage the casing). Be careful with the nuts as they are very small and delicate and a new impeller housing is eye wateringly expensive!
- Put the whole assembly back together loosely, until the next season, when reverse the above to put the impeller back in again (put it in so that it turns anti clockwise as you look at it!). Be VERY careful not to cross thread the bolts, note two are shorter than the others. Re-tension the belt by putting a long screw driver between the impeller housing and the engine and levering the pully out to the desired tension. Ensure the belt is on the pully!
- These Yanmars are notorious for their exhaust elbows disintegrating, so take it off, and check it fully! PBO published a cracking write up on this process here.
- Be very careful taking out the three M8 bolts holding the elbow on! I sheered mine off trying to access mine. Apply heat and plusgas first and go very carefully indeed.
- Check the two anodes and replace if necessary. One is on the back of the engine, one is on the Stb side (marked as zinc). These are both removed using a whopping number 24 spanner, and a spanner is what I’d go for, with plenty of leverage, every day over a socket.
- Do not apply any copper grease or such to the threads as that may insulate the anodes from the engine. These are dry fit.
- Spray the whole engine lightly with WD40, concentrating on the electrical components.
- Put some paper towel up the exhaust to stop cold icy air entering through the exhaust.
If this has been helpful and you want to show your gratitude, please feel free to buy me a coffee.