5R55S Mustang Fluid Change: Type, Capacity and Cost

The short version: every 2005-2010 Mustang with the five-speed automatic has the Ford 5R55S, and it takes MERCON V. Ford's 2007 Mustang owner guide lists Motorcraft MERCON V, part XT-5-QM, at an approximate dry capacity of 11.9 quarts (11.2 L) including the cooler and tubes [1]. A normal pan-and-filter service puts back a lot less than that. The job itself is simple. What makes it a shop job instead of a driveway job is that the 5R55S has no dipstick, so the level has to be set at a plug in the pan with the engine running, the car level on a lift, and the fluid between 80 and 120°F on a scan tool [3].

Below is the full S197 service: what to buy, how much, Ford's drain and refill sequence and torque specs, the no-dipstick level check, cost, and what a fluid change will not fix. Where a number is my own shop figure and not published, I say so.

Recommended 5R55S parts

Everything a 2005-2010 Mustang 5R55S fluid service needs: Ford-spec MERCON V by the case, the 5R55W/5R55S filter and pan gasket kit, and the 307-437 style fill adapter for the level plug. Secure checkout on site.

Motorcraft Mercon V ATF - Case of 12 Quarts (XT5QMC)

$173.99View part

5R55W/5R55S Transmission Filter and Pan Gasket Kit

$46.99View part

Ford 5R55W/5R55S ATF Fill Adapter (OTC 6604 / 307-437)

$15.99View part

Which Mustangs have the 5R55S

The 5R55S is the automatic behind both the 4.0L SOHC V6 and the 4.6L 3-valve V8 in the 2005-2010 Mustang. The 2007 owner guide's VIN chart lists the five-speed automatic as transmission code L, next to the T5 manual (code F) and the TR3650 manual (code K) [1]. If you have a car with an unknown history, the code on the Safety Compliance Certification Label settles it in ten seconds.

That check matters more than it sounds. The 2011 and later Mustang automatic is a different six-speed on a different fluid (see our 6R80 Mustang fluid change guide). A parts counter that looks up "Mustang automatic fluid" without a year can hand you the wrong jug. On a 2005-2010 car, the answer is MERCON V and nothing else.

What fluid to buy

The owner guide calls for Motorcraft MERCON V, XT-5-QM [1]. That number has been superseded. Motorcraft's current part numbers for the same fluid are XT-5-QMC (quart), XT-5-5Q3M (5-quart jug) and XT-5-DMC (55-gallon drum), and Ford lists MERCON V as not for use where MERCON SP, MERCON LV, MERCON ULV, Type F or CVT chain fluid is specified [6]. Those are different fluids for different transmissions. None of them belongs in a 5R55S.

Ford also says no supplemental additives, treatments or cleaning agents; the service manual warns they "may affect transmission operation and result in internal damage" [4]. If a Mustang only shifts right with a bottle of something in it, the bottle is covering up a hydraulic problem.

The early 2005 fill

This is the one piece of history that is specific to early S197 cars. Sonnax notes that a run of 5R55 complaints traced back to the factory fill, which used an early MERCON V formula prior to May 2005. Ford's interim fix was an additive package, 4L2Z-19B546-AB, used with fluid XL-11 under Field Service Action 04B22, and the final fix was a revised MERCON V (XT-5-QM) in black quart bottles [5]. The 2005 Mustang went on sale before that change.

Any MERCON V you buy today is the revised fluid, so this isn't a reason to hunt for a special product. It is a reason to take an early 2005 car with a delayed or harsh engagement seriously when the owner says the fluid has never been changed. On a twenty-year-old original fill, fresh MERCON V is the baseline before you condemn a solenoid body.

How much fluid a Mustang fluid change takes

Ford is clear that the chart is not how you fill it. The service manual note reads that capacities are approximate and that the correct level is set by the fluid level check procedure, "rather than amount of fluid added" [4]. So the habit to build is simple: catch the old fluid in a clean, marked container, measure it, put roughly that much back in, then let the level plug tell you when it's right.

When to change it

Ford's 2006 Scheduled Maintenance Guide covers the Mustang on the normal schedule for cars, and that schedule changes the automatic transmission fluid at 150,000 miles. The level inspections on that schedule only apply to transmissions with a dipstick, which the 5R55S doesn't have [2]. In practice, nobody looks at a normal-schedule Mustang's transmission fluid for 150,000 miles unless there is a complaint.

The special operating conditions page is the one that fits a lot of these cars. Ford calls for an ATF change every 30,000 miles for towing or a car-top carrier, extensive idling or low-speed driving, dusty conditions and off-road use [2]. The 5R55W/S service manual adds hot weather above 90°F with heavy loads or hilly terrain to the 30,000-mile list [4].

My own interval for a Mustang automatic: 30,000 miles if it lives in heat, sits in traffic, or sees the drag strip, and no more than 60,000 miles on a gentle commuter. That's shop judgment, not a Ford number.

Step by step: draining and refilling a 5R55S

You need a lift (or four tall stands that hold the car level), a 3/16-inch Allen key, the Ford 307-437 fill adapter or an equivalent, a hand pump or suction gun, a scan tool that reads transmission fluid temperature, a new filter and pan gasket, and the fluid. The sequence below follows Ford's draining and refilling procedure for the 5R55W/S [4].

1. Drain the pan. Raise and support the car. Remove the large drain plug in the pan and let it drain.
2. Drop the pan. Remove the 16 pan bolts, the pan and the gasket.
3. Replace the filter. Remove the filter bolts and discard the filter. Lubricate the new filter's seals with clean ATF and make sure they are seated on the filter; Ford warns dry seals can be damaged on install.
4. Drain the converter if you can. Ford's procedure removes the converter housing access plug and the converter drain plug. If yours has one, use a new converter drain plug and torque it to 89 lb-in (10 Nm), then reinstall the access plug. Not every converter in the field still has a drain plug, so look before you plan the fluid order around it.
5. Clean the pan and magnet. Read what's on the magnet before you wipe it (more on that below).
6. Reinstall the pan. Ford says the pan gasket is reusable if it cleans up undamaged; I replace it on a car with any seep. Start all 16 bolts, then tighten in a crisscross sequence to 97 lb-in (11 Nm). Install the drain plug at 19 lb-ft (26 Nm).
7. Refill through the level plug. Remove the small center plug in the drain plug with the 3/16-inch Allen key while holding the large plug with a wrench, install the 307-437 adapter, and pump in MERCON V. If you use pressurized fill equipment, Ford says to reduce the pressure to 1 psi; more than that can push fluid out the vent, and it then looks like a leak from the converter area [4].

Setting the level without a dipstick

The Mustang owner guide says plainly, "The 5R55S transmission does not have a transmission fluid dipstick," and it sends the owner to a dealer for checks [1]. The shop procedure is in ATRA Technical Bulletin 746, which covers the 5R55N, 5R55S and 5R55W fluid level and fill plug assembly [3]:

1. Connect a scan tool and watch PID TFT. The fluid has to be between 80-120°F (27-49°C) at the end of the procedure.
2. Start the engine. Idle should be about 650 rpm. Put the selector in Park.
3. With the engine running, get the car as close to level as possible on the hoist.
4. Hold the large drain plug and remove the small center level plug with the 3/16-inch Allen key.
5. Add fluid through the 307-437 adapter a pint at a time until it runs back out of the plug. When it slows to a thin stream or drip, it's full [4].
6. Confirm TFT is still inside the window, reinstall the center plug (the bulletin's illustration gives 10 Nm, 89 lb-in), and move the selector slowly through each range.

Two Mustang-specific notes from my own bay. First, level means level. A low car on front ramps or a two-post lift with the arms set uneven will read wrong at the plug, and you'll either overfill or leave it a quart low. Second, the window is narrow. A 5R55S idling on a lift can walk past 120°F faster than people expect, so watch the PID the whole time. Check it hot after a road test and fluid runs out that belongs in the unit; check it cold and you'll underfill it once it warms up.

Drain-and-fill or flush?

Ford's maintenance guide says flushing "is a viable way to change fluid," but only with the same fluid the job finishes with or a Ford-approved flushing chemical [2]. On a healthy, maintained Mustang a MERCON V exchange is fine. On a high-mileage car that has never been serviced, I'd rather do two pan services a few hundred miles apart; our flush vs drain-and-fill guide covers that call. After an overhaul, flushing isn't optional: Ford requires the cooler and tubes to be backflushed, because debris left in the cooler is "a major cause" of repeat failures [4].

What a Mustang fluid change costs

Parts, at our prices: MERCON V runs about $14.50 a quart by the case, and a 5R55W/5R55S filter and pan gasket kit is $46.99. A pan-and-filter service with six quarts comes in around $135 in parts. A pan, filter and converter drain that takes most of a 12-quart case is closer to $220. If you're doing it yourself, add the fill adapter; without it, there is no clean way to get fluid in.

Shop labor on an S197 pan service is typically about an hour to an hour and a half once you include the level check on the lift. That's my estimate, not a published labor time. Rates vary widely by area, so ask for the fluid quantity and filter on the estimate, and ask how they set the level. If the answer doesn't include a scan tool and the level plug, go somewhere else.

What a fluid change won't fix

Servo pin bore wear. The well-known hard failure on the Mustang 5R55S is wear in the aluminum case where the overdrive and intermediate servo pins ride, which shows up as lost or flared 2nd, 3rd and 5th. Ford addressed it in TSB 09-12-12 for 2005-2009 Mustangs. Fresh fluid may soften the symptom for a few weeks, but it won't fix a worn bore. Our servo pin bore guide covers the air test.

Read the magnet. A light gray paste is normal wear. Black friction material you can feel between your fingers means clutches are going. Brass-colored flakes point to bushings or thrust washers. Pieces of steel or a snap ring mean the unit is coming apart, and the fluid change just became a diagnosis. That's my read from the bench, not a published chart.

Need parts for this job?

Our 5R55 parts page carries MERCON V by the case, 5R55W/5R55S filter and pan gasket kits, the 307-437 style fill adapter, and the solenoid packs and rebuild kits for when the magnet tells you more than a service will fix. Checkout is on site.

FAQ

What transmission fluid does a 2005-2010 Mustang automatic use?

The 2005-2010 Mustang automatic is the Ford 5R55S, and it takes MERCON V. The 2007 owner guide lists Motorcraft MERCON V part XT-5-QM, now sold as XT-5-QMC by the quart. Do not use MERCON LV or MERCON SP in it.

How many quarts does a 5R55S Mustang take for a fluid change?

Ford lists 11.9 quarts (11.2 L) as the approximate dry capacity, which only applies to an empty unit after an overhaul. A pan and filter service usually takes back about 4 to 5 quarts, and a service that also drains the converter takes more. Ford says to set the final level with the check procedure, not by the amount added.

How often should a Mustang 5R55S fluid be changed?

Ford's 2006 maintenance guide changes the fluid at 150,000 miles on the normal car schedule and every 30,000 miles under special conditions such as towing, extended idling or low-speed driving, dusty roads and off-road use. A Mustang driven in heat, heavy traffic or at the drag strip is better served by the 30,000-mile interval.

How do you check the transmission fluid on a Mustang with no dipstick?

The level is checked at a small plug in the center of the pan drain plug. With the engine idling in Park, the car level on a lift and the scan tool showing TFT between 80 and 120 degrees F, remove the plug with a 3/16-inch Allen key and add MERCON V through a 307-437 adapter until it drips out.

How much does a 5R55S Mustang fluid change cost?

At our prices, a pan and filter service with six quarts of MERCON V and a filter kit is about $135 in parts, and a service that uses most of a 12-quart case is about $220. Shop labor typically adds an hour to an hour and a half including the level check on a lift.

Related guides

• 5R55S Mustang Common Problems and Fixes
• 5R55S Mustang Slipping: Causes and Fix
• 5R55S Mustang Shift Problems
• 5R55S Fluid Type and Capacity
• 5R55S Flush vs Drain-and-Fill