The highly debated ATF engine flush...

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Mar 22, 2006
in the shop
On the highly debated topic of the AFT engine flush here are my primitive recent results... Anyhow, I am a big fan of these if one knows the maintenance history of the vehicle they are flushing. Here is my example; Our 2012 Honda Civic with 147k miles on it. We have owned this since new and I have been fairly religious about the maintenance. I usually use the maintenance minder on the car which comes in at around 8k at the 15% notice. I have done 2 or 3 10-12k runs on quality full synthetic oils that were sent off for UOA's. 90% of the OCI's were full synthetic 0w20 or 5w20. I have run maybe two or three conventional 5w30 runs at shorter 5-7k intervals. So this brings me to the flush. The ATF flush I use had evolved a bit over the years. I like the ATF since it has lubrication properties unlike kerosene. My most recent flush consisted of; -2.5 quarts of ATF (1.5 quarts of ST ATF and 1 quart of ST ATF+4) -1 quart Motor Medic engine flush -Approximately 4-6 ounces of ST engine stabilizer (Walmart's version of Lucas) Here is my primitive theory... 1) Motor medic for the cleaning portion. 2) ATF to lubricate and show the color change from the bright red. 3) The oil stabilizer to thicken it all up a little bit. The car was driven about 50 miles and the old oil was drained and filter removed. Everything drained for 30-40 minutes. A new sacrificial filter was installed and the cocktail added. The engine was run at idle for 20 minutes and then drained. I am actually very surprised at how dirty the fluid was that came out considering that the engine looks spotless through the fill hole on the top end. In my opinion, this flush works. Just my .02 on the age old topic.
Can you do a blotter test to show the difference between the clean and dirty flushes?
I already disposed of it, sorry. I did drain that through a few layers of a white cotton t-shirt and there was a fair amount of small debris that I could see.
Engines that are properly maintained never need an engine flush. You guys go 10,000 miles on an OCI and then think you have to do an oil flush. How about keeping the insides of the engine clean in the first place ?
Having tested this, the reason that Transmission fluid turns black when in the crankcase is because of the way it reacts to combustion byproducts and the heat all combined together and not having the chemistry to handle it like engine oil would because it's not meant to be in this environment. It's not because it's cleaning the dirty black stuff from inside your engine. If you want to see proof of this, do the the flush on a brand new engine the same way and there will be the same results. I have torn apart engines where oil changes were neglected and we tested trans fluid as a flush prior versus true flush products and I can tell you without a doubt transmission fluid does nothing more than using regular engine oil would do in this short period. The blackness without a doubt is the reaction and nothing more.
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A good running vehicle you've had since new and properly maintained. You think it's a good idea to run this concoction through it? crzy
I thought we established that the ATF flush is an outdated meme from the days when engine oils didn't have very good additive packages...?
ATF turns dark from the heat and combustion products...nothing to do with removing any kind of goo. If I take Dex6 over 250F it gets dark real the transmission.
Thanks for sharing SW99... So, even with the new filter, the t-shirt showed some particles in the pour-thru? Wow... How many times over the 147k miles have you done this? Afterwards, do you fill with oil and go or do a sacrificial run thru with a cheap conventional to purge?
The add pack from a basic ATF like ST is almost like a "non-detergent" engine oil. I'm not even sure it would meet SA/SB/SC specs. Likely doing much more harm than good. I'd do the flush with a cheap SN engine oil. And I picked up a bunch of those recently (QS) at 25c per quart or less.
Originally Posted By: Merkava_4
Engines that are properly maintained never need an engine flush. You guys go 10,000 miles on an OCI and then think you have to do an oil flush. How about keeping the insides of the engine clean in the first place ?
+1 Alchemists trying to turn lead into gold
No offense whatsoever, but I am failing to see any benefit. You've owned the car since new and it's been properly maintained. Why the flush? Don't fix what aint broke is a common saying here. IMO, the discoloration in your cocktail was from the old dark oil that was remaining in the engine. This would happen regardless of what oil, ATF, additives etc. you dumped in there. The red ATF just made it more noticeable.
Nice! Use synthetic and quality filter,change on time and no worries. Flushing does work sometimes BUT remember it takes off the protective oil film too.
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