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seadog47 10-06-2009 06:19 PM

yanmar 2GM20F oil burner
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 10-06-2009 06:45 PM

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.

seadog47 10-07-2009 06:43 AM

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

timebandit 10-07-2009 10:01 AM

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.

seadog47 10-08-2009 03:49 PM

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 10-08-2009 06:14 PM

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.

seadog47 10-15-2009 05:26 PM

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 10-15-2009 05:39 PM

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

seadog47 10-15-2009 05:44 PM

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

seadog47 10-15-2009 05:46 PM

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.

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