BJNoSHOV8 wrote:
>I've heard of this before and I always wondered what the purpose was.
>Any engine will wear, and there will be trace metals in the oil. If your
>analysis says that there are trace metals in the oil but the engine is
>running fine, what are you supposed to do about it? I don't think you
>would immediately put new rings and bearings in. And if you aren't going
>past your required change intervals then you just keep driving the car
>until you get indications that there are really problems with rings or
>bearing clearances.
As I said in my last post, a UOA is a tool to help evaluate oil
performance. You can't tell much of anything about oil visually so you
need a tool to interpret the invisible. You can't see or feel spark
impulses so you need a timing light to interpret them for you. Your senses
won't tell you the freezing point of coolant, the pressure in the fuel
system, the resistance of a ignition coil or the clearance in a main
bearing so you need tools to interpret that for you.
It's similar to doing, say, a compression test. You do the test
and find #2 cylinder a bit low. Not below minimum spec, just 20-30 lbs
lower than the rest. Do you immediately rebuild the engine? No. You
evaluate that one piece of info in relation to everything else you know
about the engine. You may decide since the engine runs fine, with no other
obvious problems, to simply keep an eye on that situation. You check
compression occasionally and at some point when it gets low enough you
decide to do some more diagnosis. A leakdown test shows leakage past the
valves. Now you evaluate whether a head rebuild is warranted or
not. Again, that info is evaluated in relation to other info about the
engine, your financial situation, how long you plan to keep the car, etc.
In each case, a tool can only give you one bit of info. That is
integrated with other bits of info from other tools including your own
eyes, ears, nose and years of experience. Hopefully, all that info will
lead you to correctly identify a current or pending problem.
If I were to see iron, lead and copper start to rise over several
UOAs, I'd start looking at bearings to see if I can see any wear. If I
pulled the oil pan and discovered a worn rod bearing and was able to
replace it before it trashed the crank - I just saved big bucks. By the
time I could hear a rod knock, I'd be out thousands for a rebuild.
Todd
Seattle,WA
'86 GTI, Red of course. (exciting racey car) 273,000 miles
'01 Golf TDI, silver. (new work car) 290,000 miles
'87 Golf, Polar Silver. (retired work car) 654,000 miles <- Gone to a new
home :(
http://www.pureluckdesign.com <-Ferrari & VW stuff
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