I need to change the transmission fluid on a '99 mercury villager. More than one person has recommended against "flushing" or "backflushing" it.

They tell me that the best thing to do is just drop the pan, let the fluid drain out completely, change the filter, put the pan back on then refill the fluid.

What is the downside to flushing it?

Currently, we are getting a several second "pause" before the car goes into Drive after moving the lever from Park to Drive.

... so I'm hoping that changing the fluid and filter will help.

Further, is there any sort of additive that you'd recommend to add to the transmission fluid that might help?

Thanks!

How-to Easily Change All Transmission Fluid and Filter


Example: Total Fill (13 quarts) - Initial Fill (7 quarts) = Balance (6 quarts)


1. Disconnect transmission return cooler line, at the radiator. Look for a 6 inch length of 5/16” I.D. neoprene hose, connecting the radiator (transmission cooler) to the transmission's metal return line. Place end of hose into an empty gallon jug.

2. Start engine and pump transmission fluid into jug, until you can hear it “slurp” in the transmission pan—the pan should now be empty. Turn engine off.

3. Drop and clean pan with brake cleaner. Remove and clean magnet, being sure to reinstall it in the same location. If you find what appears to be a child's toy top, discard it. It's a filler tube plug used to keep contamination out of the transmission during assembly. When the dip stick is inserted, at the factory, the plug is dislodged and remains on the bottom of the transmission pan. It is an indication the transmission fluid and filter have never been changed.

4. Remove and replace transmission filter, coating the O-ring with ATF.

5. Replace pan. If gasket is the reusable type, reuse it.

6. Add Initial Fill of ATF through the filler tube (7 quarts).

7. Start engine and pump out half of Balance (3 quarts of ATF). Stop engine and add 3 more quarts of ATF.

8. Start engine and pump out the other half of Balance (3 quarts of ATF). Stop engine and add 3 quarts of ATF. The system should now have the Total Fill of ATF (13 quarts).

9. Replace dip stick, start engine, and, with the car level, move the gear selector through each gear (PRNDL), pausing 5 seconds in each gear. Warm car up to normal operating temperature, place car in (P)ark on a level surface, and check the dip stick with the engine running. Ensure fluid comes to the top of the “Full” line.

The above approach is what I would do. Be sure to use Mobil 1 Synthetic Multi-Vehicle ATF. This will likely eliminate your problem. Synthetic ATF will thoroughly and safely clean the transmission; therefore, you shouldn't need any other additives. You should notice a significant improvement in performance.


Total Fill, 1999 Mercury Villager, 4 speed 4F20E Transmission: 8.8 quarts of Mercon V.

I could not find out the Initial Fill; however, since the Total Fill is so small, I would definitely try to change all of the fluid. Automatic transmissions on FWD vehicles are problematic and need above-average maintenance.

To take the explanation a step further, simply dropping the pan only changes most of the transmissions fluid, but not all.
Take for example a 2003 Chevy Impala. The "pan" capacity is 7.4 US quarts. The entire system hold 10 US quarts.
Most "flush" machines are designed to go inline with the transmission cooler and, in conjunction with the transmission pump, push all the old fluid out and replaces it with fresh trans fluid.
Opinions are like ideas. Everybody has one and they just know their's is better than mine.
My opinion on flushing is that it's just another option. Yes, it gets the other 25% as shown in the example, but unless you're uneasy or feel it necessary, it's probably not worth the effort.
Routine maintenance doesn't require it, but you can still get it done.

The most important points are to drop and clean the pan, change the filter, and refill with full-synthetic ATF. Mercon V is a partial synthetic (80 to 85% conventional oil.) Many quick-change outfits will connect a T-Tech machine to change the fluid, without dropping/cleaning the pan and replacing the filter. This is courting disaster. The T-Tech machine will stir up all of the crud in the pan and possibly clog the filter. Two weeks later you may experience catastrophic transmission failure. This is how a Mercury dealer near me gets a lot of transmission business from people who got their transmission serviced at quick-change outfits.

Here are the steps, if you want to do a partial change (this is how most dealers will do it):

1. Obtain proper transmission fluid and filter for your vehicle (some vehicles don't have filters). I recommend you use a full-synthetic ATF (e.g. Mobil 1 Synthetic Multi-Vehicle ATF or Amsoil Synthetic Universal ATF), provided it meets the manufacturer's specifications for your vehicle. Transmissions run cooler (because of the higher coefficient of heat), perform better, last longer, and get better gas mileage with synthetic ATF. This is cheap insurance for protecting the most complex and problematic part of your car. Do it to save money, in the long run, and protect yourself from the big unexpected transmission repair bill. Synthetic ATF offers a "margin of safety" we all need.

2. Transmission fluid should be at normal operating temperature, before draining.

3. Turn engine off and position drain pan under transmission pan and drain fluid by loosening pan bolts. Loosen one corner more than others to direct flow into drain pan.

4. Remove all transmission pan bolts and lower pan carefully.

5. Remove old filter. Some filters are held in place by a bolt or two; however, some are held by a clip. Ensure filter O-rings or seals are removed with the filter. It may be necessary, on some vehicles, to pry out the old filter seal from the transmission housing, being careful not to nick or gouge the seal mating surface. If you find what appears to be a child's toy top, discard it. It's a filler tube plug used to keep contamination out of the transmission during assembly. When the dip stick is inserted, at the factory, the plug is dislodged and remains on the bottom of the transmission pan. It is an indication the transmission fluid and filter have never been changed.

6. Install new filter using the same bolts or clips. Use new O-ring or seal supplied with the filter.

7. Inspect pan carefully before cleaning. Small amounts of fine gray clutch dust are normal; however, if you find metal shavings, there could be transmission damage or mechanical problems.

8. Clean transmission pan thoroughly with solvent (e.g. brake cleaner) and wipe dry, so there is no harmful residue. If there's a magnet, it should be cleaned and replaced in the same position in the pan. Clean transmission and transmission pan mating surfaces of all gasket material, being careful not to damage the surfaces. If the transmission didn't come with a drain plug, I recommend installing a B&M Transmission Drain Plug in the pan at this time. It makes subsequent changes a snap. Carefully choose a location for drilling a 1/2" hole for the plug. Some manufacturers emboss a "0" where the hole should be drilled. Install drain plug, nylon washer, nut, and torque to 20 ft.-lbs.

9. Position gasket on the pan. Some gaskets have four slightly smaller holes, to allow four bolts to hold the gasket in place.

10. Hand-tighten transmission bolts in a crisscross pattern until snug. Use a torque wrench to tighten bolts to proper torque.

11. Refill transmission through the dipstick, using the amount shown as "refill capacity" in the owner's manual.

12. With vehicle on level ground, recheck the fluid level, using procedures outlined in the owner's manual. This frequently involves starting the engine and pausing several seconds in each gear, as the gear selector is run through the complete gear range (PRNDL). Check the transmission and lines for leaks. The final fluid level check is usually made after transmission reaches normal operating temperature, engine is running, and transmission is in Park.

This approach may only change 4.4 quarts, or less, of ATF in your Villager.

Which is approximately half of the 8.8 USQ capacity!

The Villager has a pan drain capacity of 4 quarts, and a total capacity of about 9-10. On your initial change, you should pull the pan off and clean it out well. Don't be alarmed if you find a small amount of metal filings on the magnets, and some dark sludge in the pan. This is normal. Large amounts of metal bits, or black, burned fluid are not normal, and probably indicate your transmission is on borrowed time. Since this unit has a drain plug, you can then change fluid regularly when you change your oil. Using generic Mercon and changing it on the same schedule as your oil will greatly prolong your transmission life, you won't need any fancy fluids or additive. The Nissan transmission used in the Villager does not have a filter as such, just a screen, so it's not worth buying, unless you need it to get the gasket. It's hard to find stores that stock just the gasket. You'll need to pull about 5 bolts out of the valve body to get the "filter" off, so you may want to skip it.