Lehman 120 blue gray smoke

[RedRascal]

Looking at a boat with a 120 Lehman with somewhere between 3,500 to 4,000 hours on it. No record of a valve adjustment, injector R&R or injector pump rebuild. Did not see engine cold start but saw it start after sitting about 4-5 hours after it's first start of the day which was just idling at the dock. Engine was probably 100 degrees when I saw it start for the second time and blew a blue/gray smoke cloud about 20' x 30'. Enough to gas out any neighbors sitting in their cockpit. After about a minute the blue went away and settle with the gray output in the pictures below. Since the engine had already ran earlier, would it be expected to see blue smoke? I thought oil leaking past the valve guides from sitting would have been burnt off with the first start so new blue smoke 4-5 hours later seems like oil is leaking past the valve guides in a short amount of time. So is this an issue to be concerned about or is there another source for the blue smoke? I am assuming it's not the rings since it stopped after about a minute. I am assuming the gray is a combination of cold engine and questionable efficiency of the injectors and pump at current service level. The blue is what concerned me.

 

[Lepke]

Blue smoke is oil. Valve guides usually don't leak much. I think rings. Most engines as temps rises causes the rings to seal better. If you are looking to buy, I'd do a compression check. If compression is ok, I'd check the injector tips. Changing oil might help.
If the engine idled for long periods, I'd suspect a lot of diesel in the oil. It has been shown that the lower combustion pressure of long idle times doesn't make the rings seal as well so more fuel washes into the oil. Lightly diluted oil helps carry the oil past the rings. Rings are designed so that combustion pressure forces them against the cylinder walls.
There are a number of studies of idle times combined with oil tests showing long idle times put diesel into the oil. It's better to warm the engine for a short period, a few minutes, and then go.

 

[Mainecoast]

Looks about average for a Lehman....once it warms up to operating temp and under load, it should clear up substantially.

 

[RedRascal]

Still wants to puff some blue smoke after motoring at cruising speed then back to idle. At cruising speed it's just a bit of light gray. However engine may have a 170 degree thermostat in it since it didn't pass 172 degrees measured at the thermostat housing with a harbor freight IR gun. Temp gauge on dash said 180 vs gun of 170. Harbor Freight vs ancient gauge so still a bit of an unknown. Talked to Brian and American Diesel and his suspicion is 170 degree thermostat vs 180. He commented that running below 180 will create smoke. Engine is smooth otherwise.

 

[mvweebles]

Blue smoke is oil. Valve guides usually don't leak much. I think rings. Most engines as temps rises causes the rings to seal better. If you are looking to buy, I'd do a compression check. If compression is ok, I'd check the injector tips. Changing oil might help.
If the engine idled for long periods, I'd suspect a lot of diesel in the oil. It has been shown that the lower combustion pressure of long idle times doesn't make the rings seal as well so more fuel washes into the oil. Lightly diluted oil helps carry the oil past the rings. Rings are designed so that combustion pressure forces them against the cylinder walls.
There are a number of studies of idle times combined with oil tests showing long idle times put diesel into the oil. It's better to warm the engine for a short period, a few minutes, and then go.

Since the OP is in the pre-purchase due diligence phase, @Lepke gives excellent advice. Cost of a compression test is reasonable and will keep you from wondering for a long time.

I've never owned a FL120 but the #6 cylinder seems to have a history to overheating. Might want to rule this out to ensure your ownership is as-expected.

Good luck with whatever you decide.

Peter

 

[SteveK]

Another thought. The hose from the valve cover usually is terminated at the air cleaner so oil vapours are burned off. Engines in my experience are filled to the high mark on the dipstick without determination for where the engine wants the level to be.
As I have often said let the engine tell you the level it wants as it will expel the extra and then you add oil, expel/add.
It could be burning extra oil