[TSOJOURNER]

I have twin saildrives using the Yanmar 2GM20F engines. They have about 3500 hrs on them and worked fine last season. This year one of them is burning oil. Both engines start about the same. I'm assuming that a diesel won't start well if rings or valves are bad and having two engines side by side it seems I can rule out rings and valves so I' thinking valve stem seals might be the culprit. I took an oil sample but have not sent it out for analysis yet. Does this logic make sense?

 

[scottyt]

normally burning oil is either rings or intake valve seals. exhaust valve seals let oil out of the exhaust unburnt. you can normally narrow it down by running the engine and see if the oil cap is under pressure, that will normally mean rings.

start the engine and open the oil cap to see if it has a lot of pressure or flow of "air" out. if it does not i would lean towards valve seals, or head gasket. both of which can be done with some simple tools if you know what your doing.

 

[TSOJOURNER]

Thanks, the boat just got hauled but I can run it long enough to check that out.

 

[timebandit]

Intake valve seals usually show themselves at start up as a bit of smoke and clears up.

Do you service these engines yourself?

If not could they have been serviced with different oil in each engine? Sometimes it makes a difference.

 

[TSOJOURNER]

I'm using RotellaT 30w and have used 15-40in the past. The port engine I believe is the culprit as it was down a qt. while the other is fine. The burning oil smell occurs pretty often not just at startup. I have the shop manuals and am not afraid to tackle anything short of the critical parts( injector pump and injectors.

 

[badsanta]

I would not touch the injector pump other than to bleed it if you dont know what your doing. imho

It could be that it was not filled all the way last oil change and what you smell is unburned diesel because of prop, bottom fouling. Maybe you just hooked some rope or fishing line in the prop. Check that first before you start spending money.

 

[TSOJOURNER]

Well I ran the engine and no back pressure on the oil cap when removed. I noticed my coolant reservoir was empty and the pan under the engine has oil in it. I know I had a small leak around the fuel pump at high rpms but the burning oil smell is outside by the exhaust. I'm leaning towards a blown head gasket now. Is it worth sending an oil sample for analysis to narrow this down or should I just grab the wrenches and pull the head?

 

[badsanta]

Check your oil level. Is it higher than normal? Oil mixed with antifreeze? I dont think a one time oil sample will tell you much. If you have the skill, then pull the head, but I would still check for a fouled prop firt. imho

 

[TSOJOURNER]

Boat is on the hard- no fouled prop just a few barnacles.

 

[TSOJOURNER]

Boat is on the hard- no fouled prop just a few barnacles. The oil level was low when I changed it. I have a qt of the old oil that has been sitting for 10 days. It is not milky in color - just the usual black color. There is no coolant separation in the sample either.

 

[badsanta]

Have you checked the exhaust elbow yet. It will rust and clog up after awhile and is to be changed every few years so I am told. I had similar problems as you. I found an oil leak on the external oil line, antifreeze from the water pump and had a barnacle encrusted prop. It was an adjustable prop and when I serviced it I did not set it right and it ran worse than ever. I reset it properly and it runs fine. My exhaust elbow was so blocked I dont know how water got through. At higher RPMs I also had a foul oil smell that is now gone. From what I read that alot of yanmar 2gm and 3gm30 are over propped and never get to cruising rpm before they start smoking.

 

[TSOJOURNER]

The exhaust elbow is a great idea and a good first step. I have about 3300 hrs on these engines but only about 1200 under my ownership. I'll bet they are original. This diagnosis makes more logical sense in that at the end of last season everything was fine but right from the start of this season I had this problem. I have 15x9 two blade folding props and run around 2800 rpm. I know some folks with the same boat(PDQ 36) run 16x9 or 11 and claim to have no problems. I have a set of 16x11 blades the PO had put on but claimed that she couldn't get the rpms. Personally I think the yard didn't fit the zincs correctly as my two hubs are different and require grinding about 1/8" of the face of the zinc. On my first haulout I had to have the spline replaced because the prop nut had not been tightened, likely because it bound on the zinc when new.