Residual flush in oil?

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Jan 23, 2014
Since not all of the oil is drained during an oil change, does the remaining flush do harm when in the motor?
If it's doing harm with that <1% of flush left in there, imagine all the harm it was doing to your engine when you had all of your flush in there!
Such a small amount shouldn't be a problem, but if you want to be super sure, do a 100mile OCI on a cheap hdeo instead of using a flush. It works out a touch more expensive but we BITOGers pay to sleep well at night
Originally Posted By: Nick1994
If it's doing harm with that div>

To be fair 15 minutes of idling even if harsh seems minimal as opposed to 10,000 miles of various driving conditions
The modern engine flush products are detergent based to be considered harmless. A decade ago, these were solvent based with naphtha, toluene and a few other volatile solvents. I would not be concerned about a little engine flush left behind unless your oil is very thin.
A week ago Thursday I went to a dinner put on by Exxon-Mobil, the old school engineer that gave the talk was rabidly against engine flush products, there was almost foam coming out of his mouth when he spoke about them. He graduated from Purdue in '73 though, maybe flush products have changed since then.

Remember, when you do an oil change you only change 80% to 90% of the oil in the engine. If you want to be sure, use the flush product then fill with fresh oil and idle for another 15 minutes, then do your oil change. That should get the flush product down to under 2%.
Purposely adding "fuel dilution" for want of a better word to my new oil change is not something that I consider desirable.

I have used solvents (diesel and kerosene) as a home made flush in an engine that I had that had litres of black grease through it from sludge, but that was a reclaimation project, not a generally un-needed routine maintenance activity.
We typically use Seafoam which can be ran full time.
All but the oil in it cooks off in time anyway. Even if we only idle it for 20 minutes with the Seafoam in the oil (1.5 oz per quart) the oil seems to get darker. With todays oils if you do not go over 15K miles should not really need flushing. I do expect flush is more for our emotional needs than the needs of the engine.

We just changed the oil in the Ford 429 engine and both diesel tractors and did the Seafoam at idle thing. The tractors have no oil coolers so with by changing the filter at the same time I think we get close to 100% of the old oil out. We do chase with 4 oz of new motor oil until the last stream of the change goes clear as the new oil but I guess that is an over kill.

We have tested filter only changes with the 429 engine and was able to clear up the oil because the Rotella synthetic really was cleaning up the old engine. Plus on it we only put 400-500 miles a year on it so it only gets changed every 4-5 years with one or two filter changes and top off.

Added Archoil AR9100 for the first time that is to double the OCI so will see how that goes. Lower friction would be good but mainly we are going for the deep cleaning action reported by the marketing department. It is a hot product for the Ford diesel with the stiction injector issues I read because of its deep cleaning action I read. We got one gallon so we can try it in all engines. You use 1.12 oz. per quart of motor oil which cost about $10 for a 5 quart engine which is cheap if you can 2x OCI.
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