Oil analysis - understanding the need.

[Rikds]

Has anyone had this done for their diesel engine? What will one find out from such a test? Can it indicate anything about compression ratios? Was it worth it?

 

[lpdsn]

Had one done as part of a pre-purchase survey ten years ago. Cost £60 IIRC. Didn't really tell me much. Oil had been recently changed (by PO). Engine had moderate wear, which was considered what you'd expect for the age.

I guess if it had found major faults it would've been worth it, except by the time it had arrived we'd already completed the re-haggling based on the surveyor's report.

 

[Fr J Hackett]

An oil analysis will tell you how much metal is in the oil and the condition of the oil and any contaminants. As a one off it is unlikely to be of any use unless the oil hasn't been changed and the engine is wearing badly when you will see evidence of metal wear but that needs to be assessed as part of ongoing maintenance.
It is useful for fleet maintenance of heavy plant but for a boat engine and most certainly on a one off basis it is virtually of no use especially as an owner is likely to have changed the oil.

 

[RichardS]

Has anyone had this done for their diesel engine? What will one find out from such a test? Can it indicate anything about compression ratios? Was it worth it?

As others have said, all it will tell you is whether the oil has been changed at an appropriate time recently or whether it is well overdue. You can probably gain almost as much by just looking at the oil on the dipstick. It should also tell you whether there is any water/antifreeze in the oil but, once again, close examination will probably indicate such a fault.

It won't tell you anything about compression ratios.

Richard

 

[Rikds]

Perhaps compression ratio is the wrong expression.
If there was diesel in the oil as a result of damaged piston rings presumably the compression in the cylinder with damaged rings would be lower?

 

[penberth3]

...It is useful for fleet maintenance of heavy plant but for a boat engine and most certainly on a one off basis it is virtually of no use especially as an owner is likely to have changed the oil.

+1

Diesel in the oil doesn't always come from the cylinders, there are other possible sources. There is a simple test for this anyway without the full chemical analysis.

 

[simonfraser]

had mine done on the engine and on the leg which both had old oil in.
analysis was all within normal limits, which helped in the decision to buy the boat, or not.
cost is minimal vs the purchase cost of the boat / possible major head aches.
i did the analysis right at the end of the boat inspection and negotiation.

 

[vyv_cox]

I used oil analysis for years professionally and even with properly organised regular sampling, results could be confusing and clearly incorrect. Sampling technique needs to be very precise and always from the same source. The method I suppose most people would use, drawing oil from the sump using a Pela or similar, is unlikely to be representative. I doubt very much that a single sample is ever going to be capable of indicating an engine fault.

 

[AntarcticPilot]

Several other threads have suggested what others here say - that oil analysis is of no use unless it is done regularly, so as to observe trends.

 

[VicS]

Has anyone had this done for their diesel engine? What will one find out from such a test? Can it indicate anything about compression ratios? Was it worth it?

Something to do regularly at the same intervals as you do for the oil in your car engine!

 

[solent clown]

Anyone with an oil analysis fetish is very welcome to the 15 litres I have just pumped out of our bilges.