Method for switching oils

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Nov 16, 2002
I know many of us on here go back and forth between brands of oil to sample and experiment with. Do you think that when switching brands, you could add about half the sump capacity of the new oil you want to run for about an hour and then drain it and fill it back up fully with the new oil? For instance, I'm running D1 and M1 but will be sending off a sample soon. If I wanted to try GC or Amsoil 0w-30, I was thinking of putting 2qts in (half of 4qts) and running my engine for an hour or so and then draining it back out and filling it up.
buster, I really do not think that this is going to do alot for you. If you really wanted to get the old oil out then run GC for 2000 drain it out and refill with more GC. Running a 50/50 mix and draining is not going to do much. No matter what oil you put in their is going to be some left behind. The only way around this is to waste GC in a short cycle. I really do not think that the left over oil is going to alter the results in a significant fashion. Every UOA you have done to date would reflect the oil you put in and the left overs from previous oil.
John, I'm not running a mix of 50/50 to get the old oil out. I'm just running that to see the results. Maybe I wasn't clear. I meant if you run a half of what your car holds for an hour, drain that out, and then fill fully up to get the full effect. [Cheers!]
What I did on my recent switch isn't perfect, but it's a start. I switched from Schaeffer 5w30 to GC 0w30, and I drained out the old oil for 15-20min, then put in 3L of GC 0w30 (normal capacity 5L) and a new cheap oil filter, and ran the engine for 2 minutes. Then I drained that oil for 10min, changed the filter, and poured in 5 more liters of GC 0w30. By doing this I ended up with 99% of the GC in there, which allows me to better see how it's viscosity holds up. I do realize that since I switched from a moly oil to a non moly oil, that the first interval will benefit from the moly still being plated. I figure the third interval will be a more true test, since the second interval will be in the wintertime anyways. I was the one who suggested to 3MP that when he switches oils for his testing, that he run a 1000 mile interval with the new brand of oil first, then drain it (and put it in one of his other cars so it doesn't go to waste) and put in a fresh batch. This method should work out well for him. He mentioned he might even do a 2000 mile "buffer run" with the oil instead of 1000, just to give himself a bit of a break from sampling for a while. [Smile]
  • 1, remove the drain plug let the oil drain.
  • 2,while the oil drains,change the oil filter.
  • 3, replace the drain plug add the oil of choice,the proper amount and type of course.
  • 4, start your engine check for leaks
  • 5 ,Turn engine off check the oil level clean up the mess if any and dispose of the used oil and filter properly.
  • 6, [Cheers!]
[ September 13, 2003, 02:21 PM: Message edited by: Steve S ]
Too much risk there. I think that as long as you give the oil an hour to drain off with the car good and hot you have less than 10% of the old oil left. And if you go from an oil that has no molly to something like M-1 with it there would be no problem. The only time that it could be significant is if you go to some other oil with no moly from Redline that has some 600 ppm. Then the new oil might have say 60 ppm or so-maybe more. The resullts of that oil might be better than without the previous oil being Redline.
Half the oil capacity is too little for most engines. Even if you filled and drained with the new oil after a short spell, the new oil will not show results immediately. Normally we look at the 3rd oil change to be more representative of what the oil is doing. The first change has a slight mixture and begins cleaning or coating, second is closer, third shows real results if the earlier oil was not too bad. I've seen some analisis that didn't show much wear particles on the earlier oil, but the first two changes of a better oil show rapid depletion of detergents, TBN, and high wear metals, coming out thick within 1000 km. The new oil starts looking good once all the crud is out. If your oils are similar and good, maybe the second change is representative.
The amount of old oil left will depend on the engine. What I saw of the insides of the Quad 4 in my Grand AM, there weren't any big places for oil to hang up. My 77 LUV has 2 places that may retain as much as a quart, the top of the head around the cam, and the oil pan in front of the clearance for the tie rod. When I change the oil, I work at bouncing the suspension, but I am sure it still leaves quite a bit of oil no matter how long I let it drain. I have run Pennzoil dino most of the life of the truck, so mixing is not an issue, but I know I leave dirty oil in it every change.
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