effect of amount of make-up oil on UOA accuracy...?

[97tbird]

By the time I'm ready to take a smaple of my oil for the UOA, I'll have added 0.75 to 1 qt of oil (GC). This is for about 3700 miles, on a Ford 4.6L sohc(97) (I associate this consumption partly with the previous oil being dino, and the switch to syn, in spite of Arx, came at 93k miles for this car...) I was wondering if this amount of make-up oil can affect the UOA in a way that the UOA is "senseles", and the numbers are really not what they should have been? But then I've seen a lot of UOA's with even more make-up oil added(in comparision the no.of miles on oil), and that noone really has any bad comments about it. Is there a limit amount where you can say "with that much make-up oil, the UOA is wasted!"? I just want to make sure that my UOA numbers still being able to give me useful info about my engine... btw, I'll be getting the Dyson package. Any thoughts/recommendations are greatly appreciated.

 

[97tbird]

bump...

 

[haley10]

I would expect your consumption to slow down, at least somewhat, later. The uoa will still be 100% useful, especially with Terry's input. Under 5K miles, I'm not sure TBN is totally worth it. We already know about what it's going to be if there isn't a major problem. All wear metals will still be accurately reported, etc. Go for it.

 

[Cutehumor]

it's not how much you add but when e.g you are 2500 miles into interval, you notice your a quart low, add a full quart..500 miles later take a UOA sample. e.g you are adding 70-80 ml oil every 100-200 miles, at the end of the OCI 3000, you added one quart. I would expect this second example to be an overall representative of what's going on in the oil

 

[Schmoe]

Based on the percent of new oil added and miles it accumulated, you would have to off-set your ppm amounts by ratio and proportion. If it's less than half a quart, normally not much. But more than a quart every 1K or so miles, it could change you amounts by about 1/3.

 

[97tbird]

Thanks for all the input sofar, guys. If it helps in anyway: as far as I can remember, my add-up intervals have been very similar; I added make-up oil on only 3 occasions: I added ca. 0.25 qt after every 1200 miles(+/-, but pretty much accurately, I can say). So you guys think it's worthwhile to do the uoa afterall...I'll do it!

 

[427Z06]

I would say this is one more reason to use caution when pointing to a scattering of other peoples' UOAs and trying to come to any definitive conclusion.

 

[TallPaul]

quote:

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Originally posted by 427Z06: I would say this is one more reason to use caution when pointing to a scattering of other peoples' UOAs and trying to come to any definitive conclusion.

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Yep, these definitely are not controlled laboratory experiments.

 

[ekpolk]

quote:

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Originally posted by haley10: I would expect your consumption to slow down, at least somewhat, later. The uoa will still be 100% useful, especially with Terry's input. Under 5K miles, I'm not sure TBN is totally worth it. We already know about what it's going to be if there isn't a major problem. All wear metals will still be accurately reported, etc. Go for it.

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I'm starting with the Dyson program too. Looks like a great service. Only comment I'd add would be that a low mileage TBN might be worth it if the time interval is long. This is the situation with my wife's car -- she just doesn't drive all that much. Her present oil is over six months old, and has a whopping 4k on it so far. Of course, it's in a Toyota 4.7L V-8, so I expect the UOA to be fantastic, but you never know. I'll still check it to be sure.

 

[TallPaul]

What if you adjusted the miles. For an oversimplified example, say you had a 4 quart capacity and at 2000 miles had to add 1 quart. Would that not then be like 1500 miles since you replenishied 1/4 the oil. Then say you drove a total of 4000 miles and had the UOA. Using the adjustment you could apply the UOA results as if you had only driven 3500 miles. Or is it not quite that simple? Anyway, I have to do something similar with my latest UOA on my motorhome. It has a 6.5 qt capacity, I added about 50 oz during a 4400 mile trip (in about 6 increments), and worse yet, ended up about 8 oz overfilled by the end. So that UOA may be more representative of a 3000 mile OCI. Anyway, I will note all that when I post the results (just mailed sample this Monday) and see what the feedback is.