yanmar sb8 using a lot of oil

[kielboatsa]

I have a 1978 hunter 27 with its original Yanmar SB8. I have owned the boat for 5 years. For as long as I have owned it it goes through a lot of oil, a littel more than a quart for each gallon of diesel. The engine always starts easily and runs great. I do not much smoke from the exhaust although I do get some soot. Soot stains develop around my exhaust after just 20 minuets of motoring in and out of the harbor for the day. There is a little oil in the bilge under the engine, but not much, certainly not anywhere near the quantity I am losing.

Does anyone have any suggestions as to what is wrong and what would be involved in fixing it? I day sail on lake michigan and usually only run the engine to motor out of the harbor and back in with the longest period of running it being about a hour or two.

 

[kloudie1]

MAN.. that is a good bit of oil.. The three big places for oil to go is 1. out with bilge water.. there is an external oil line on that engine .. The line can rust through and leak or the connections can leak. 2. Piston rings.. worn piston rings will allow a lot of oil to get burnt during running.. but that can usually generate blue smoke.. A lot of the smoke will be washed out of the exhaust by the cooling water. That washing will generate a kind of greasy soot..This can also be caused by a glazed cylinder wall from not being run hard enough. 3. Valve guides.. If the valve guides and seals are shot you can get a lot of oil loss ..
Fixes.. First, a compression and leak-down check will tell you if the piston rings are worn out. or the cylinder is glazed..These two are fixed the same way.. new rings and deglazing the cylinder.. While the cylinder head is off, fix the valve guides and recondition the valves..
All but the oil line leaks are fairly expensive repairs if you don't do them yourself.. If the oil line isn't leaking, consider how cheap motor oil is ; you may decide to continue to run for a while before rebuilding..

 

[kielboatsa]

Thanks,
that is what I am afraid of (expensive repairs). For my current type of sailing, the oil only costs about $30 per season. It is just like the 65 dodge I use to drive, I can buy a lot of oil before I come close to the cost of the repair.

 

[Benny17441]

What oil grade are you using? If you have ruled out an oil leak then it is likely the oil is being burnt or expelled out the exhaust port. I would suggest you switch to a higher grade oil like SAE 40 and add an additive like STP or others. This will increase compression and reduce burning. You indicate you do not run the engine much and I'm wondering if it reaches recommended operating temperature in these short runs in your cold waters. A multigrade oil requires for the engine to attain operating temperature for the oil to reach maximum thickness. If it does not you may be running with to thin of an oil. Now the downside is that a heavy single grade oil will slow down the cranking process when starting the engine in cold weather.

 

[kielboatsa]

Thanks Benny,

I will give the higher grade oil a try this coming season. Will need to wait a while since it is 1 degree F today in Chicago and I saw a dog and its owner walking across my harbor today!