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Old 06-03-2018, 09:20 AM
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smj999smj smj999smj is offline
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2006 Pathfinder
2003 Frontier King Cab
2003 Frontier KC SVE 4x4
 
Join Date: Jun 2012
Location: Prospect, VA
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I think people confuse the process for engine flushing with that of transmission flushing. Most commercial automatic transmission flushing machines are nothing more than fluid exchangers. They don't have pumps to pressurize the fluid, rather a tank with a bladder that separates the old fluid from the new fluid. The lines of the machine "T"-in between the radiator cooler hose and the "exit side" radiator cooler fitting on the radiator. New fluid is poured into the machine, typically 12-13 quarts, which fills the tank on one side of the bladder. The vehicle is started and the old fluid is routed into the machine into the opposite side of the bladder, which pushes against the bladder and forces new fluid to get pushed into the cooler hose and back to the transmission. So, the only pressure is the normal line pressure to the cooler circuit created by the transmission, itself, which can vary as low as just a few PSI to around 12-13 PSI, depending on the vehicle. Now, a lot of these commercial fluid exchangers are often associated with companies that sell additives, like BG products. So, often a pre-conditioner is sold as part of the service and added the trans fluid before the flush process and there may be a conditioner to be used after the flush that is also sold as part of the service. How beneficial they are or even necessary is debatable. DIY'er types can do the same thing without the fancy exchanger or the chemical additives. They simple remove the AT dipstick and install a trans funnel and get a case of the correct ATF. The "exit" side cooler hose is disconnected and ran into an appropriate container to catch the old fluid. The line back to the transmission is plugged off. The engine is started and as old fluid slowly fills the containers, a similar amount of new ATF is poured into the funnel until a case of ATF has been exchanged.
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