How Long Would You Run 2 or 3 "flush" OCIs When Changing Oil Chemistries?

[RevvCats]

I switch oils constantly, I’ve never run the same oil twice in my Mustang, and don’t worry about it one bit. Never had any signs of additive package clash leading to increased wear.

Just keep in mind what you had in and how that might skew future results. I’ve been running a few different flavors of Castrol Edge this past year and I’m sure it will take quite a few oil changes before the titanium levels drop to zero. Same goes with using an oil that contains esters, that will bump up your oxidation values if you switch to a non ester.

That’s why I don’t like comparing anything to unused samples because that comparison just doesn’t exist in the real world. When I look at how oils hold up to track use I sample at the start and end for that reason.

 

[garageman402]

Change oil. Start engine, running up to temp, stop engine, change oil again. Basically it takes about 20 mins total.

Been there, done that, analysis shows still residual oil.

 

[SubieRubyRoo]

Been there, done that, analysis shows still residual oil.

What’s the problem with residual oil? It’s a very small volume in the big picture, and it was lubricating your engine just fine when drained. VOA/UOAs don’t tell you anything about the performance of the oil as far as wear protection is concerned… I guess I’m lost as to why you’d even consider wasting several quarts of oil (or more) even if money isn’t an issue.

I’m no treehugger by any means, but pointless waste is one of the 7 deadly sins (gluttony).

 

[TiGeo]

Folks here are missing why he is asking about this...he wants to flush the old oil fully to get a UOA that is representing the new oil, not because they are changing brands/types. Re-read the OP. I'd go with LSJR on this one and get 2 full changes, maybe just run them shorter like .5-1K miles or so to speed up getting your data.

 

[ripcord]

In that case flushing will likely give lower contaminate counts on subsequent UOA tests... so still not a terribly useful thing to do.

 

[SubieRubyRoo]

Folks here are missing why he is asking about this...he wants to flush the old oil fully to get a UOA that is representing the new oil, not because they are changing brands/types. Re-read the OP. I'd go with LSJR on this one and get 2 full changes, maybe just run them shorter like .5-1K miles or so to speed up getting your data.

The ending point of the oil in the sump is always what the UOA shows; a little residual oil left over will probably have less effect on the UOA than a simple change in driving habits. The inquiry and intent of the OP is fine; however the means to get a “clean” UOA are nearly irrelevant other than giving you a slightly smaller circle of probability where the next UOA will land.

You should know, Ti, from experience on your own vehicle and your work, that a small handful of ppm one way or another over a proper quantity of samples to perform statistically significant analysis averages out as noise alone, which is what the residual oil is.

A jump in wear numbers by 30-50ppm or exceeding UCLs for fuel, silicon, potassium, or sodium are the warning factors one should care about, and those are visible whether there’s residual oil or not in the sample. I understand the question, but just like the “I made this change and my mpg went up/down”, there’s too many uncontrolled variables involved here to bother wasting the time and resources to attempt to get a 100% “clean” UOA. Do the VOA, and use it as a reference to see what was left and if any warnings have shown up. Use the “flush” oil for your next change.

 

[BMWTurboDzl]

Been there, done that, analysis shows still residual oil.

Okay so do it twice. The amount of residual oil is going to vary by engine.

 

[garageman402]

Folks here are missing why he is asking about this...he wants to flush the old oil fully to get a UOA that is representing the new oil, not because they are changing brands/types. Re-read the OP. I'd go with LSJR on this one and get 2 full changes, maybe just run them shorter like .5-1K miles or so to speed up getting your data.

Thanks, but I was actually asking because of changing brand/types, I have read about competing chemistries causing issues & skewing a UOA. As I mentioned the analyst said he found additives that are not in the new oil I was running, so could be skewing the results. He said do three oil changes to get a reliable assessment. Yes, looks like 2 full changes are in order, maybe 100 miles would be enough?

Keep in mind that oil blenders (even big ones like Mobil) will change formulas with some frequency. So, for example, the Mobil1 EP you buy today may have different base stocks and additives than that you bought a year ago. So I wouldn’t worry about it.

Right, but this was a major change I made, IIRC, a number of years ago.

"Should" not be damage, but you are pushing your luck to the wall. Running an engine 2.5-3 qts low is a really bad idea. And for a flush?

Yes, "should" was a poor choice of words, positively no damage as long as the pressure stays the same would be correct. LSJ ran 5 quarts in an 11 quart pan & oil pressure dropped a little at 5400 RPM. He called it "windage" but seems to me like it was sucking air. Then he added 2 more quarts & pressure held steady until like 7000 RPM. Then he filled it up & it stayed up throughout the entire range. Said it cost 16hp, but at what price in engine wear? My point is 5 quarts in an 11 quart pan (6 quarts low) ran with no adverse effect until 5400RPM. In my case 3 quarts low had no adverse effect, unless I ran the engine some insanely high RPM, which I did not.