How long before synthetic takes over the old dino?

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Dec 8, 2003
No this isn't a question of when synthetic will be the type of oil "ALL" people use. It is a question of how long it takes to clean out the old dino in an engine. I switched to Mobil 1 5w30 at 89,000 miles in my 1997 Tahoe, it was fall and getting colder so I went with 5w30. I have had it since 60,000 miles and as far as I know the previous owners used dino up to that point. I used the valvoline, halvoline, quick change places until 89,000. I am wondering how long it takes for the old dino to completely get out of the system using synthetic such as M1? It now has 98,400 miles and am getting ready for its 100,000 mile tune up changing the plugs, wires and whatever else is needed. I know there are a lot of factors like how clean the engine was before, how much sludge had built up over the years with dino oil, how well it was taken before I bought it (not very well since I had to put in a new tranny at 69,000), etc... Since changing to M1, the first two OCI's were done before 3,000 miles. I was getting anxious and wanted to keep putting clean stuff in. Now after almost 10,000 miles, I just changed to the 10w30 a month ago and plan to go 5,000 miles. Is it safe to say that most if not all of the old dino is out of the engine? Thanks someone needs to make a thread over the synthetic becoming mainstream [Big Grin]
Well, the Mobil 1 by itself will probably not cleanup the deposits left by the dino oil. You'll need AutoRx to do that. Every oil change gets out about 85 to 90 percent of the old oil. So as far as the old oil-you are O.K with that-but the deposits will still be there probably.
I thought ARx should only be used if your engine is running rough. I read a post on here saying, don't use it if you aren't having problems.
Unless you have a tremendously gunked up engine, I'd think that the arithmetic of dilution is the "lead factor" in answering your question. As an example, my car takes 5.0 qts with a routine oil and filter change. By the service manual, the fill amount is 5.8 qts if you've done an overhaul resulting in complete draining of the entire oil system (a dry block as it were). So on any routine change, approx 0.8 qts of the old stuff "automatically" remains behind. Look for your "dry engine" number, compare to routine change numbers, and do the math from there.
Mathematically speaking, the oil in your engine will NEVER be 100% synthetic. There will always be some dino left, however tiny the amount. Using the 5.8 qt/5 quart example above, changing the oil with 5 qts M1 leaves .8 qts of dino, which then mixes with the Mobil 1 making it 86.2% M1, 13.8 % dino. At the next oil change, you drain 5 more quarts of M1/dino (leaving .8 quarts)and add 5 quarts of M1. Mathematically, that makes it 98.1% M1 and 1.9% dino after two oil changes. After then NEXT oil change, the percentages are 99.73% M1 and 0.26% dino. You get the picture. Point is, it will never be 100% but it quickly becomes statistically insignificant. P.S. Anyone is welcome to double check my math. I am Asian, after all, but apparently the Calculus gene skipped a generation. [Big Grin]
Originally posted by DonCT: P.S. Anyone is welcome to double check my math. I am Asian, after all, but apparently the Calculus gene skipped a generation. [Big Grin]
WTF is that??? Reverse self discrimination? [Roll Eyes]
Just a simple fact. I have two cousins that are engineers. One was valedictorian of Cornell, one at Stanford. I never got above a B in any math class since second grade. I failed calc in college and to prove it wasn't a fluke, I repeated the class and failed again. [Smile] But I can shoot a rifle and play chess better than anyone else I ever met and those are both mathematical pursuits so go figure. [I dont know]
Got to agree with Don. Your going to lower the percentages with each change, but unless you absolutely steam clean the engine, your going to have some dino in it. As long as the oils had the same ratings, SL, I surely wouldn't be loosing any sleep over this.
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