Can UOA miss a bad engine condition?

Joined
Jun 13, 2022
Messages
195
Came across a oil consuming corolla

The engine had crazy blow by, beat up rod bearings causing a knock on startup, and burned tons of oil. Overall, the motor was in very very bad shape. I expected metal shavings and lots of other crap in the oil. They got an oill analysis back that read normal, with everything measured at or below averages, except for a higher viscosity from some Lucas that had been added. Recommended to run 5k more on that oil. When tearing it down for rod bearings were thoroughly chewed up.

Is a single UOA unable to determine such wear?
 
Joined
Aug 25, 2018
Messages
2,961
Location
South Carolina
ICP only looks at particles <10 um in size. If you have a bunch of big chunks of metal >10 um swimming around in the oil, they won't show up on UOA. A UOA will usually not tell you about a sudden, catastrophic failure. It's to observe trends over repeated oil changes to look for signs of excessive wear occurring. It's also possible for a high efficiency filter (particularly a bypass filter) to capture a lot of particles out of the oil, leaving little to show in the sample.
 
Joined
Dec 4, 2013
Messages
638
Location
Maryland

There is a section on this Forum that explains everything or most of it about Used Oil Analysis
 
Joined
Dec 26, 2005
Messages
22,944
Location
Upper Midwest
Singular UOA are limited. When I ran oil analysis in college without an acid digestion of the sample particles are not typically measured. As explained in the posts I link here the ICP is not a particle measurement device.

 
Joined
Apr 15, 2010
Messages
7,814
Location
Connecticut
UOAs are great for determining the condition of the oil, which can give hints on the condition of the engine, but isn't an accurate way to diagnose anything. The BMW M car guys seem to use UOAs to check for rod bearing wear, but it isn't always a good indicator. I'd be willing to bet that in those cars you'll hear a rod knock before you see bearing materials elevated enough to cause concern. A UOA gives a snapshot of how the engine is wearing over a given mileage interval, not how worn it is in general.
 
Top