Tranny flush or fluid exchange?
 

My 1999 Grand Marquis now has 50,000 miles on it, and I'm told it's time to service the transmission, even though it runs perfectly. Should I get a tranny flush or just a fluid exchange? I know the flush get new fluid in everywhere (including the torque converter), while the fluid exchange only gets half of new fluid in there. Thanks in advance!

At 50,000 miles, you're already past the recommended service period -- so you need to start over.
DO NOT FLUSH -- I repeat -- DO NOT FLUSH your 4R70W Transmission !!
Factory Shop Manual says to CHANGE the Fluid and the Transmission Filter, which means that the transmission AND torque converter must be drained and re-filled, and the Transmission Filter replaced at the same time.
Transmission Fluid = MERCON V
The Transmission Fluid capacity is:
13.6 U.S. Quarts
12.9 Litres
DO NOT OVER-FILL !!
Transmission Filter = Motorcraft FT-100 (Made in USA)
Comes without new gasket -- original gasket is RE-USABLE !!

The so-called transmission "FLUSH" doesn't flush out the dirt and debris at all, it ONLY changes the fluid -- the dirt and debris stays in there !!
Proper trans service is performed by dropping the pan, draining the trans AND torque converter, replacing the filter, and re-filling with MERCON V trans fluid.

Thank you so much, Merc. I was waiting for your wonderful reply. Your advice in the past has been great!

Tranny Flush ??
 

All-ways glad to help another Grand Marquis owner, GS -- we're getting scarce !!
I do almost all of my vehicles' maintenance and repairs at home -- I can plan my jobs, research necessary parts, order parts on-line, and have them delivered to my door. Easy-peasey.
RockAuto.com has a HUGE variety of parts, and excellent product info to help make decisions.
I get many parts from Amazon.com, as well. Amazon's return policy is outstanding.
Anyways, back to the tranny !!
I completely forgot to mention that the trans pan must be dropped in order to clean the internal ceramic magnet that's in the bottom of the Trans pan.
Dropping the pan allows an inspection and thorough cleaning of the pan's interior and the magnet
The original factory pan gasket is re-usable many times. NO SEALER is ever used or needed when the original pan gasket is re-used.
Just clean the original gasket with WD-40, and you're good to go !
Tighten pan bolts to 120 inch/lbs., using a cross-hatch pattern.

Everything went perfectly yesterday. Drain, new filter, and new Mercon V.
This is absolutely the best car I've ever owned.
Thanks again.

You're good to go for another 35,000 miles ! !
With decent care and maintenance, your Merc should perform well for many more years.
I bought the 95 MERC in 2005 -- @ 51,000 miles.
It now has 157,500 on the clock, and runs beautifully, easily passing our emissions testing with flying colors.
Best of luck with your "new" Mercury.

Your 2005 Marquis has two (2) tranny filters -- one is an in-line filter, and the other filter is inside the trans pan.
Your 2005 internal filter is changed the same way as the 1995 -- drop the pan, clean it thoroughly, and clean the ceramic magnet that's in the bottom of the pan.
Clean the original pan gasket with WD-40, and re-install. -- Tighten pan bolts to 120-inch-pounds, working in criss-cross pattern..
NEVER, EVER use a cork gasket on your trans pan !!.
I use CASTROL Transmax Mercon V Trans Fluid -- Shifts are sharp and smooth, good fuel mileage..

Glad to be of help, especially if you are gonna run your Grand Marquis on the infamous "Road to Hana" !! ;>)