Transmission flushing at home: Really easy, really effective

[Pennhaven]

Here is the temp vs level chart, as you can see, the temperature makes a dramatic difference in what the reading should be, you gotta have a way to check the temp....

[Edit]Since there were two incorrect assumptions in the original post, I have rewritten it to avoid confusing anyone else.[/edit]

I found the temperature/level chart to be confusing, but now, after a few more hours straightening out a mistake I made, it makes more sense. I had a difficult time correlating the markings on my dipstick to the diagram on the chart, as the relative spacing on the dipstick is significantly different than on the chart. Especially the distance between the HOT and COLD areas.

But, leaving the relative scale of the chart aside, I am sure that the chart is indicating that at 40°C the level should be somewhere in the COLD area and at 80°C it should be somewhere in the HOT area. You can also use the chart to interpolate the correct level range for in-between temperatures, but that is a lot more difficult given the differences in proportions between the chart and the actual dipstick.

I checked my "cold" level before I flushed, when the transmission was truly cold (20°C), and found that it was slightly below the COLD area on the stick. After flushing the new cold level was about 1/3 of the way between the COLD and HOT areas, so at first I thought that I needed to pump out about 3 oz. But this was assuming that the 0.2L (6.6 oz) range was between the COLD min and the HOT max. My first bad assumption. The 0.2L range actually refers the difference between min and max levels at a given temperature. I finally figured this out after several attempts to pump out 3 oz. at a time were barely moving the level.

At first I thought the problem was that the temperature was changing while I was measuring, so to nail that down I came up with a process to minimize the temperature variation. I used an indoor / outdoor thermometer from Radio Shack. I could not get an accurate reading by placing the outdoor probe on the case of the transmission, so I resorted to inserting it in the dipstick tube, with a knot in the lead so it would go in no further than the length of the dipstick. This worked fine. I found with the engine running that the fluid temperature would rise about 0.1° C every 15 or 20 seconds. And since I could not measure the temperature while I was using the dipstick, I decided to shut off the motor and let the temperature fall slightly below 40°C then start the motor, and take two measurements with the dipstick before the temperature could climb above 40.5°.

Now I knew I had a valid temperature and accurate level, but my level was to still too high. It would not drop as much as I expected. It was then that I figured out my assumption about the 0.2L was wrong.

But why was my level so high? (It eventually turned out to be 25 - 31 oz. too high!!) That was caused by my second bad assumption. I assumed the 16 oz. graduated cup I was using to measure the discharged ATF was accurate. It was not! After checking I found it was over-reading by about 8%! This would not have mattered if I had used the same cup to measure the new ATF going in, but instead for refilling I relied on the assumption that each bottle of ATF contained exactly 32 oz. and used the graduations on the bottles to measure ounces when needed.

So lesson learned. If you do not use the same device to measure both output and input, be sure that all devices agree.

BTW, my flush went very well otherwise. My only issue, other than overfilling, was that some fluid apparently dripped out of the return line while it was disconnected. I didn't notice the spill in the drip tray behind the radiator until I was cleaning up. Good thing I didn't see it while I was flushing or I probably would have added another oz. or two to compensate and overfilled even more!

I also changed my coolant while I had the belly pan off, and I found that to be very easy too. Probably the easiest coolant change I have ever done, due to the handy petcocks on the rear of the block and under the radiator.

Thanks again Gibbons for posting your transmission flush instructions and now the chart from VADIS.