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Yanmar power loss

Mar 31, 2013
9
Catalina 320 Long Beach
I have a Yanmar 30 hp with 400 hrs that makes terrible noises above 2000 rpm. It starts and runs great below 2000 rpm, with no smoke and little noise. The fuel is 2-3 years old. Could that be the cause? Adding SeaFoam didn't help. I'm thinking of replacing the fuel before getting a diagnosis. I did notice a little antifreeze in the last oil change.
 
Jan 7, 2011
1,507
Oday 322 East Chicago, IN
Antifreeze in the engine oil?

That sounds like a head gasket to me.

Greg
 
Nov 6, 2006
8,445
Hunter 34 Mandeville Louisiana
Antifreeze in engine oil is never a good thing. Head gasket problem.
 
Jan 12, 2016
212
Hunter 410 Ladysmith, BC
I have a Yanmar 30 hp with 400 hrs that makes terrible noises above 2000 rpm. It starts and runs great below 2000 rpm, with no smoke and little noise. The fuel is 2-3 years old. Could that be the cause? Adding SeaFoam didn't help. I'm thinking of replacing the fuel before getting a diagnosis. I did notice a little antifreeze in the last oil change.
Does it make the sound only when in gear or also when in neutral?
 
Mar 31, 2013
9
Catalina 320 Long Beach
Thanks the replies, guys. It makes the noises when in gear or neutral. I guess I do have a bad head gasket, even though it only has 400 hrs. It is 14 years old. Before I have it overhauled, could there be any other cause other than a bad head gasket for antifreeze in the oil?
 
Dec 14, 2003
1,081
Hunter 34 Lake of Two Mountains, QC, Can
How do you know you have antifreeze in the oil ? Brown bubbles or brown residue (sometimes crusty) above oil level on dipstick could be an indication. Or a chocolate milk color. Before overhauling, I would check torque on head and manifold. then change oil, filter and water separator. After that, you could run the engine pulling clean new fuel straight out of a jerrycan, checking your oil at regular intervals during your tests to make sure it is clean. If it foams or changse color again then youmight need to pull the head and have it resurfaced, reinstalling with a new head gasket. good luck.
 
Mar 29, 2017
321
Hunter 30t littlecreek
You say 14 yr old 30 hp so it's a 3gm30.
Do you have a engine Manuel the valve trane needs adjustment every 100 hr and a pressure test is possible while your in there maybe retorq head while valve cover off adjusting