Yanmar 4Jh2E when to rebuild/replace?

[Miguelso]

New to this forum, so Hi to Everyone !
We bought our boat about a year ago and it has a Yanmar 4cyl. It runs great, starts in a second every time, even in cold weather, no knocking nor excessive vibration, but it smokes blue (it can use some paint too). Most noticeable when cold and less afterwards. The hour meter was broken and stucked in 5k hrs so it probably has way more hours than that, but not much more info about it's history. I know blue smoke means its burning oil, but after about 30 hrs I didn't notice any change in the oil level. I wouldn't pay much attention to it if I would use it only to get in and out of the dock or maybe to motor for 50 hours during the summer. But next year we are planing to go down the ICW and to the Islands, so I'm debating with myself with "if it's not broken don't fix it" and that I don't want the engine to ruin our trip. Any thoughts?
Thanks,

Miguel

[Ericson38]

[QUOTE=Miguelso;2000568]New to this forum, so Hi to Everyone !
We bought our boat about a year ago and it has a Yanmar 4cyl. It runs great, starts in a second every time, even in cold weather, no knocking nor excessive vibration, but it smokes blue (it can use some paint too). Most noticeable when cold and less afterwards. The hour meter was broken and stucked in 5k hrs so it probably has way more hours than that, but not much more info about it's history. I know blue smoke means its burning oil, but after about 30 hrs I didn't notice any change in the oil level. I wouldn't pay much attention to it if I would use it only to get in and out of the dock or maybe to motor for 50 hours during the summer. But next year we are planing to go down the ICW and to the Islands, so I'm debating with myself with "if it's not broken don't fix it" and that I don't want the engine to ruin our trip. Any thoughts?
Thanks,

Miguel[/QUOTE

The oil control rings could be partially stuck. I really doubt that it is valve guides or valve stem seals.

Perform to back to back oil changes, 10 hours apart.

Afterwards get a compression check. Get a real oil pressure check, at operating temperature.

I would not overhaul it. Use the money some other way.

Make sure the RPMs it maxes out to are in the ball park, and keep the fresh and raw water systems in good condition.

It may have sit around for years without proper oil changes, which will cause rings to stick.

Black smoke is an injector dribbling or not spraying correctly, but blue is oil burning.

[a64pilot]

Yanmars are notoriously smoky motors, comes from incomplete combustion, it may well be fuel, especially if it dissipates pretty quick, oil smoke will not dissipate.
If it starts easily, doesn't smoke up the anchorage, has good oil pressure, runs well and doesn't consume an excessive amount of oil, then there is nothing to fix.
I bet if you Google smoky Yanmar, you will get a lot of hits.


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[Miguelso]

Thanks, I'll try the back to back oil change and the test the compression before doing something radical.

[Viedeau]

I have been asking that question for ever, and they say IF MAINTAINed 10k is reasonable. Tractor trailer trucks run several hundred k miles, which is 6000 hours at 300 without idling . I added 250 going from DE to Fl, and about half on inside