Will makeup oil skew UOA?

[wn1998]

The Auto in questions is a 1997 Cavalier 2.2L with 195k. I started with 4 quarts of Amsoil ASL 5W30 and an Amsoil EAO oil filter. I have used synthetics on this car since 145k. It has also had 3 auto rx treatments in the last 3 years.

Anyway, I had to add about 1/2 quart of Mobil 1 5w30 (extra stock) at 3,000 miles and I just added another 3/4 quart of Maxlife full synthetic at 7k. My cavalier has a 4 quart sump and I plan to do a used oil analysis at 10k/6 months. Is a used oil analysis worth the money?

 

[Harley Anderson]

I can't answer that question on a spectro-analysis standpoint but make sure you let the lab know how much makeup oil you've added. I know with my diesel application, I've added 8 quarts of oil on my last used oil analysis for filter changes and the numbers were pretty much all inline with a used oil analysis that had no makeup oil.

If you continue to run Amsoil a used oil analysis is beneficial to see how long it will last and protect the engine under the conditions you put on the motor. It will save you money in the long run.

 

[addyguy]

For sure it will skew the results - it will change additive amounts somewhat, as different oils use different add's in different amounts. It will also 'boost' the TBN of the oil, and leave it higher than if no oil had been added.

That being said, don't let this affect your plans for a UAO - it will still give you an idea of how the engine is wearing, and will tell you how long you can run your oil. Plus, what else are you going to do - you have to add oil when it is low, or the engine runs out of oil, so on an older engine, you probably can't get an exteneded OCI WITHOUT adding oil, thats just life!

On a personal level, I would LOVE to see your UOA when you have it, as I have an '02 Cavalier 2.2 with 104k miles, and I'm considering doing 10k-ish OCI's with a syn...I like too see used oil analysis on this engine, as there aren't as many as there are for some engines....

 

[FZ1]

Topping up the oil replenishes the additives and TBN. It's like a mini oil change. I keep my oil at the top mark on the dipstick and try to add an ounce every month. It's just southern engineering for those who don't do a used oil analysis. The fact that your car uses more oil means the oil is fresher....as long as you top it up. Just my .02.