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850 S70 V70 C70 Transmission Flush

Published on February 3, 2011 by Bay13

A lot of information concerning the changing of transmission fluid has been floating around. I would like to explain what I think is the best preventative maintenance and how often you should change the fluid. Older vehicles had a requirement to change the fluid every 20 thousand miles. The older RWD transmissions did not have lock up in the lower gears. Fluid needed changing every 20K miles. My experience with the newer FWD transmissions has been at a dealer that has a total flushing machine. I have found that between 20 and 25 thousand miles the fluid begins to turn brown and pick up a burnt smell. Although the newer FWD transmission should be gentler on transmission fluid, time has shown that the fluid still needs changing. Below is a photo sequence of what the flushing entails.

Above is the flush machine. Many different companies have their own models. The principle of operation is; the machine is filled with 15 quarts of new fluid, the two blue hoses are connected in series with the transmission lines on your vehicle. The car is ran, and the vehicles transmission pumps the fluid out into the bottom of the machine that has a bladder that is pushing up on the new fluid forcing it into the transmission. Notice in-between the two gauges is a sight glass to monitor the fluid change.

Above shows the lines connected into the top of the radiator. Below shows the fluid at the start of the flush and then at the end. Kind of speaks for its self. This vehicle had 22,790 miles on it. You may not need a fluid change this soon, monitor your fluid color and smell. You can even send a sample out for analysis should you want to get a second opinion. Blackstone Laboratories,4929 S. Lafayette Street, Fort Wayne, IN 46806, (219) 744-2380 or on the web at

The transmission could be flushed/refilled by you at home using new, clean transmission fluid, meeting DEXRON III G specifications. (Total volume needs to be at least16 liters) Check your owners manual to make sure of the type of fluid you should be using.

Remove the battery and battery shelf. Remove the return hose on the control system (valve body). Install a plastic plug in the connection on the cover (valve body) and a transparent plastic hose on the oil return hose connection. Position a container for the oil with markings for the volume under the hose. Temporarily reinstall the battery shelf and the battery.

Apply the parking brake, gear selector in park, start the engine and allow the engine to idle. Switch the engine off when 2 quarts of oil have been pumped out or when air bubbles become visible in the hose. Top up with 2 quarts of oil. repeat this procedure 7 times. Check the color of the oil, when the color of the oil is clear red (as new oil), switch off the engine and connect the return hose to the control system (valve body) cover. Check and adjust the oil level.

The above procedure is the official Volvo procedure for flushing the transmission. It is a bit simpler to disconnect the top connector at the radiator, you can do this just know that you will not be flushing the cooler when you do this. Transmission Fluid should last forever, but driving conditions and time have shown that things dont always turn out in real life like they do on paper. The newer transmissions with lock up in the lower gears as well as some transmissions even go into neutral at a stop should make the fluid last longer, keep your eye on the fluid condition and change it when needed. (your mileage may vary)


Transmission Line Removal

To remove the transmission line pry open in the direction of the yellow arrows to open the clip, and then pull in the direction of the blue arrow. This is the top connector and it is the one we disconnect at the shop. The top hose is the fluid coming from the transmission, the connection down at the bottom (Green arrow) is the fluid returning to the transmission after passing through the radiator for cooling.

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