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Old 03-26-2020, 02:31 PM   #1
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Engine oil analysis question

Someone I know paid $1,100 for a boat survey including oil analyses of both diesel engines on the boat. The samples were pulled before the engines were started, ie., they were cold.

Everything I have read on this says the samples should be pulled after the engines have been warmed to operating temperature, generally at least a half hour.

What is the correct procedure?
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Old 03-26-2020, 02:36 PM   #2
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I don't think that the temp of the oil is the determining factor. What concerns me about a cold sample is that some of the heavy metals may have sorted themselves out, therefore your sample may be high or low on these items, depending upon where you draw the sample from. Same for other contaminants such as water, fuel, antifreeze.

Starting the engine and bringing it to temp will "homogenize" all these foreign elements.

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Old 03-26-2020, 02:57 PM   #3
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The sample needs to be drawn from a engine at operating temperature. So the oil, any water and debris is mixed, not settled to the pan bottom. Better yet, I take samples often enough to install a petcock in the oil line so I can take samples with the engine running.
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Old 03-26-2020, 03:05 PM   #4
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Yes, up to temp before pulling the sample.
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Old 03-26-2020, 03:17 PM   #5
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I assume this would be the same for samples from the generator and the transmissions?
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Old 03-26-2020, 03:39 PM   #6
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Yes.
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Old 03-26-2020, 04:23 PM   #7
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Thanks for the quick response, much appreciated!
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Old 03-26-2020, 04:45 PM   #8
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A record of previous oil samples provided by the seller would be much more valuable.
1. It would show that he cared.
2. It would enable you to spot wear trends.
Be sure to find out how many hours are on the present oils.
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Old 03-26-2020, 04:47 PM   #9
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Ideally you would have at least 50 hours of so on the oil before you get it analyzed. Otherwise the oil may not show any problems yet.
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Old 03-26-2020, 04:57 PM   #10
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Lengthy thread on this recently on Cruisers Forum.com, with some heated exchanges both for and against the efficacy. Will leave that debate for another day.

Good article by Steve D. I had a video of him explaining best practices on pulling a sample but I can't find it right now. Suffice to say, cold engine that hasn't been run in a while is worst case. Best case is a tap to draw a sample while running. Normal is to pull a sample from at least an inch off the bottom of oil pan when engine is warm.

https://stevedmarineconsulting.com/o...m_export=print

Peter.

Thread on CF if interested. Took me a while to understand that oil samples are often used to determine when to change the oil which is a good practice, though not exactly practical for typical trawler engines, and even less so for sailboats, the typical on CF.

https://www.cruisersforum.com/forums...d.php?t=231256
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Old 03-26-2020, 05:00 PM   #11
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BTW. What the hell kind of mechanic charges $1100 and pulls a cold oil sample? Are you sure? Would mean they pulled the sample first, then did the mechanical survey.

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Old 03-26-2020, 05:36 PM   #12
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I'll agree with the engine should be up to temp.
I too have added a small valve so I can get my sample while the engine is running.
I use a small peanut butter jar to collect some purging oil before I take the actual sample so there is no debris that got trapped getting flushed out at the initial valve opening.
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Old 03-27-2020, 05:54 AM   #13
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The key to oil sampling is to have a bunch to use to compare .

IF the P.O. did not sample,, a single sample , even taken correctly , might only show a really poor engine ready to hand grenade.

Many folks selling a boat will change the oil , so it looks cleaner, USELESS for oil sampling.
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