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Old 14-05-2021, 13:16   #1
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Diesel Oil Analysis prior to purchase

New member here .... I am currently looking at a used boat with a diesel engine. I've been reading a bit about oil analysis and I'm wondering:

- Is an oil analysis useful if you do not have a history of previous oil analysis from that engine for comparison purposes?

- Does the oil analysis give you any indication of how long it has been since an oil change? If not, couldn't the seller just change the oil then run for an hour or so to mix it up, then tell me that it has been 60 hours since the last oil change? The oil analysis report would be very favorable if the oil had only been in the engine for an hour runtime, right?

- Any other "service record" type of items that would be good to have?

Thanks.
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Old 14-05-2021, 13:52   #2
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Re: Diesel Oil Analysis prior to purchase

Quote:
Originally Posted by James827 View Post
New member here .... I am currently looking at a used boat with a diesel engine. I've been reading a bit about oil analysis and I'm wondering:

- Is an oil analysis useful if you do not have a history of previous oil analysis from that engine for comparison purposes?

- Does the oil analysis give you any indication of how long it has been since an oil change? If not, couldn't the seller just change the oil then run for an hour or so to mix it up, then tell me that it has been 60 hours since the last oil change? The oil analysis report would be very favorable if the oil had only been in the engine for an hour runtime, right?

- Any other "service record" type of items that would be good to have?

Thanks.
I didn't even find the oil analysis that useful managing maintenance for a large fleet of aircraft with the oil samples taken religiously at fixed intervals and a history that went back to the last overhaul of the gearbox or engine. All the points you make about the gaming opportunities make it even less useful. I would say this, if it comes back clean it doesn't really tell you anything. But it could come back with a bunch of metal and that would be useful information. I'd stick with compressions and a borescope if you want to be thorough.
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Old 14-05-2021, 13:59   #3
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Re: Diesel Oil Analysis prior to purchase

Not always as useful as people think they are ......
Oil_Analysis_on_Diesel_Boats
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Old 14-05-2021, 15:04   #4
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Re: Diesel Oil Analysis prior to purchase

In my admitted limited experience in buying boats, most owners would frown upon someone removing injectors. They may allow for glow plugs to be removed but I believe them to be in the minority.

An oil analysis, if taken after a full temperature run-up, can provide some information and be a reasonable value for the cost. It won't confirm a good engine but it can identify excessive internal wear or coolant ingress issues.
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Old 15-05-2021, 04:14   #5
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Re: Diesel Oil Analysis prior to purchase

Greetings and welcome aboard the CF, James.
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Old 15-05-2021, 04:28   #6
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Re: Diesel Oil Analysis prior to purchase

I'll never forget the time I was showing a boat's owner how to check the oil on his Westerbeke. After a demonstration of both locating and pulling the dipstick, I noticed the oil was as black as coal and immediately followed-up with our Head Mechanic and double-checked our records re the most recent oil-and-filter change. All was up-to-date.

"It always does that", Head Mechanic said.
(News to me!)

Anyway, lesson learned was that depending on the type of engine, even after a brand new oil-and-filter change (and even with the good, regular maintenance that we did for this particular boat), the oil can still look frightening.

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Old 15-05-2021, 05:02   #7
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Re: Diesel Oil Analysis prior to purchase

Good article by Steve D'Antonio on the topic. I personally would absolutely do an analysis if for no other reason but it's the first data point in a regime of periodic oil analysises to establish a trend. While some faults can be masked by a recent oil change, other components are unacceptable at any ppm of presence (sodium - salt water intrusion) so if they are there - even in a recent oil change, point to a problem.

https://stevedmarineconsulting.com/oil-analysis/

Oil analysis is not the definitive result some hope for, but its definitely a useful set of data. For $40, it's it's pretty good deal.

Peter

PS - LittleWing: years ago I had an old Peugeot 504 diesel sedan that would go black immediately. I argued with an oil change place that they had taken my money but didn't do the oil change. Boy, did I feel stupid....
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Old 15-05-2021, 07:01   #8
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Re: Diesel Oil Analysis prior to purchase

Quote:
Originally Posted by James827 View Post
New member here .... I am currently looking at a used boat with a diesel engine. I've been reading a bit about oil analysis and I'm wondering:

- Is an oil analysis useful if you do not have a history of previous oil analysis from that engine for comparison purposes?

- Does the oil analysis give you any indication of how long it has been since an oil change? If not, couldn't the seller just change the oil then run for an hour or so to mix it up, then tell me that it has been 60 hours since the last oil change? The oil analysis report would be very favorable if the oil had only been in the engine for an hour runtime, right?

- Any other "service record" type of items that would be good to have?

Thanks.
IMO a single analysis use is very limited. If “clean” it may mean nothing, if “dirty” it just means more investagation.

Now if the engine has had regular oil analysis than can be compared that is a different story.
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Old 15-05-2021, 07:08   #9
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Re: Diesel Oil Analysis prior to purchase

I have a Weterbeke 55A. After an oil change the oil stays pretty clear and shows not much darkening til' I get about 10hrs on it.

I have two friends with 55A's and their oil is black within seconds of an oil change.

The difference ....
I put a drain on the bottom of my oil pan to a 12volt pump and get every last drop out. They use those hand pumps with a tube down the dipstick. They are lucky to get 75% of the old oil out.
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Old 15-05-2021, 09:04   #10
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Re: Diesel Oil Analysis prior to purchase

Welcome to the forum!!

- Is an oil analysis useful if you do not have a history of previous oil analysis from that engine for comparison purposes? Yes, it will tell you if there is water contamination and excessive corrosion in the transmission and/or engine

https://www.boatingmag.com/how-to/be...-oil-analysis/

- Does the oil analysis give you any indication of how long it has been since an oil change? No If not, couldn't the seller just change the oil then run for an hour or so to mix it up, then tell me that it has been 60 hours since the last oil change? They Could The oil analysis report would be very favorable if the oil had only been in the engine for an hour runtime, right? Maybe

- Any other "service record" type of items that would be good to have? Yes, have a engine survey performed prior to purchase as that will give you a good baseline of the engine condition and what maintenance has to be preformed, if any. You would want to know whether the engine is cooling properly, propeller and engine properly matched, fluids O, etc.

https://stevedmarineconsulting.com/t...engine-survey/
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Old 15-05-2021, 10:28   #11
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Re: Diesel Oil Analysis prior to purchase

I agree with Kenbo, and as a Broker urge prospective buyers to get an oil sample of motor(s). Yes, the seller can try to game system, but a good seatrial and motor “run up” will result in a valid oil sample, if there is excessive wear and moisture issues. I also recommend transmission oil samples and particularly with a sail drive unit.
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Old 15-05-2021, 11:10   #12
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Re: Diesel Oil Analysis prior to purchase

Paid $80 for it when purchasing our boat. Found a little diesel in it which led to the seller paying for a lift pump fix, more run time to confirm fix and a new (clean) oil analysis. I'd recommend it.
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Old 15-05-2021, 13:07   #13
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Re: Diesel Oil Analysis prior to purchase

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Originally Posted by redneckrob View Post
I didn't even find the oil analysis that useful managing maintenance for a large fleet of aircraft with the oil samples taken religiously at fixed intervals and a history that went back to the last overhaul of the gearbox or engine. All the points you make about the gaming opportunities make it even less useful. I would say this, if it comes back clean it doesn't really tell you anything. But it could come back with a bunch of metal and that would be useful information. I'd stick with compressions and a borescope if you want to be thorough.

What he said. A one time will tell you if there is there large quantities of metal, but a borescope and compressions will give you a great idea of the overall condition of the engine. I also did oil analyses on aircraft and it only another set of data that you may not need. If you need to feel comfortable go for it, but don't foreget the borescope and compression checks.
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Old 15-05-2021, 13:41   #14
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Re: Diesel Oil Analysis prior to purchase

Out of curiosity, how many owners would allow a compression test/borescope on say a Yanmar without glow plugs? I know I wouldn't. Falls in line with why surveyors do not remove anything during a survey. In most cases, a properly performed oil analysis and full temperature run-up is about as good as your going to get to assess the running gear.

I fully agree that a compression test and borescope is more informative on an engine you own or have been authorized to evaluate but on a pre-purchase survey?
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Old 15-05-2021, 15:34   #15
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Re: Diesel Oil Analysis prior to purchase

Hi James

I have been looking for a new boat and just rejected one on the result of oil analysis. It has recorded 80hrs since last oil change. Total of 1500 hrs on the clock. It showed Fe, Chromium, Sodium, and an additive which the report said was consistent with coolant. There was no water. There were two engines both recorded significant metal contamination. With a rebuild cost of over $20k each I think the cost of the analysis was worth it. But the engines did run nicely yet one engine was overheating slightly.
Maybe I was a bit cautious but the mechanic said chrome indicates wearing of hard metal surfaces such as camshaft etc.
Boat was great otherwise.
Still looking for another.

Cheers
Woody.
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