AutoTips Automatic Transmission Fluid Changing Tip:
You may want to do a partial change under these conditions: Changing transmission fluid can be a messy job. On many cars, there is no drain plug, you have to drop the pan and let out the fluid. One of my cars had a drain plug, but although the manual said the transmission had a 7 quart capacity, only 3 quarts drained out of the plug. The car had a second part of the case that held fluid, and a hump between it and the drain pan. Getting access to the second area would have required removing the engine and transmission.
On checking the fluid on a used car I bought, the fluid was dark brown, and the weather was bad. I wanted to get the old fluid changed as quickly as possible, but didn't want be under the car outside to do it.
Often, a simple drain may not get all of the fluid, you will have fluid in the torque converter that may not drain out, or in the cooling lines.
It is always best to drain completely and change, but if you can not, this may help. Many auto parts stores sell manually operated fluid pumps. You may be able to use one of these to pump some fluid out of the dipstick tube. This is NOT a substitute for a full fluid and filter change, but you can dilute down some of the old fluid. In my cars, I was able to remove about 2 quarts through the dipstick tube. I measured the amount I removed, and replaced with a equal amount of fresh fluid. I repeated this over several days, allowing driving time to mix the new fluid with the old.
Fluid pumps are available in various types.
NOTE this only dilutes the old fluid. After about three changes, the fluid was starting to look better. When the weather was better, and I had the time, I did a regular change & replaced the filter.
Benefits: When you change, fluid left in the system that doesn't drain out will be a mixture of old fluid and new, not only old.
If you remove fluid through the drain tube before a change, there is less fluid spilling out to catch when you lower the pan. (Not a problem for a professional shop, but if you have your car up on ramps in your driveway, it can help)
If weather, and or time prevent you from doing a full fluid change, you can improve the condition of your fluid.
Disadvantages: You risk buying a pump and not being able to get any fluid out the automatic transmission dipstick tube.
You can not clean deposits out of the pan, and may miss evidence of other problems. You only dilute old fluid plus it takes more fluid. Be sure and buy the right type of transmission fluid for your car. Always check the owners manual for the right type. And if you are not sure, go to a professional and/ or consult a shop manual for your car.
You can do a similar partial fluid change on power steering pumps, use the fluid pump to remove power steering fluid from the reservoir, and replace with new ( of whatever type the manufacturer specifies ). Repeat a few times with driving in between, and the fluid will be mostly new.
For an excellent source of more information on transmissions, etc. check out:
The Drive Train Page
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