5R55S Fluid Type and Capacity

The short answer: the Ford 5R55S takes MERCON V. Ford lists an approximate dry-fill capacity of 11.2 L (11.9 quarts) in the 2007 Mustang and 11.7 L (12.4 quarts) in the 2007 Explorer, per the owner guides' Maintenance and Specifications capacity tables (Sources 1 and 2). The part that trips people up isn't the fluid. It's the fact that this transmission has no dipstick. You can't check it in the driveway, and you can't set the level by feel. Ford's procedure uses a scan tool, a lift and a level plug in the pan, and it only works in a narrow temperature window.

This guide covers what Ford and the transmission trade actually published for the 5R55S: the fluid and part numbers, the capacities by vehicle, the no-dipstick level check, the service intervals, and a few service traps that have caused comebacks on this unit. Every spec ties to a source at the bottom. Where a number is my own shop experience and not a published figure, I say so.

Recommended 5R55S parts

What a correct 5R55S fluid service needs: Ford-spec MERCON V, a 5R55W/5R55S filter and pan gasket kit, and the 307-437 style fill adapter for the level plug, since there is no dipstick. 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

What Ford specifies: MERCON V, part XT-5-QM

The 2007 Mustang owner guide lists Motorcraft MERCON V ATF, part XT-5-QM, for the automatic, and names the transmission outright: "The 5R55S transmission does not have a transmission fluid dipstick." The 2007 Explorer guide lists the same fluid and part number for its 5R55S. Ford says the fluid type is also marked on the transmission itself, on the pan or extension housing, which is worth reading on any vehicle with an unknown history.

XT-5-QM is the part number printed in those guides. Motorcraft's current numbers for the same fluid are XT-5-QMC (quart, sold in cases of 12), XT-5-5Q3M (5-quart jug) and XT-5-DMC (55-gallon drum), per the Ford Customer Service Division fluid page.

The Explorer trap: two automatics, two fluids

This is where I see the most mistakes. The 2007 Explorer guide lists two automatic transmissions side by side: the five-speed 5R55S on MERCON V, and the six-speed 6R60 on MERCON SP, part XT-6-QSP. They are different fluids for different units. Ford's footnotes spell it out: a MERCON V transmission should only get MERCON V or a fluid labeled dual-use MERCON/MERCON V, and a MERCON SP transmission should only get SP, because a dual-use fluid in an SP unit may cause damage.

So before you pour anything into an Explorer or Mountaineer from this era, find out which transmission it has. The VIN tells you. Ford's VIN decoder in the 2007 Explorer guide lists transmission code V for the five-speed 5R55S and X for the six-speed 6R60. On the 2007 Mustang, the 5R55S is code L. It takes ten seconds and it saves a wrong-fluid comeback.

What not to put in it

Motorcraft lists MERCON V as not for use where MERCON SP, MERCON LV, MERCON ULV, Type F or CVT chain-type fluid is specified. None of those is the spec for a 5R55S. The 2007 Mustang guide adds that a non-approved fluid may cause internal damage and void the warranty. It also says not to use supplemental transmission fluid additives, treatments or cleaning agents, because they can affect operation and damage internal parts. If a 5R55S only shifts right with a bottle of something in it, it has a hydraulic problem that the bottle is hiding.

The early MERCON V note

Sonnax's 5R55 identification article carries a detail worth knowing on this family. It notes that early complaints were tied to an early MERCON V formula, prior to May 2005, and that Ford's final solution was the revised MERCON V (XT-5-QM) sold in black quart containers. Any MERCON V you buy today is well past that change. The takeaway for a shop is simpler: if you're chasing an old engagement or shift complaint on a 5R55 that hasn't had a fluid change in a long time, fresh MERCON V is the baseline before you start condemning parts.

Capacity by vehicle

Read the footnotes before you trust either 5R55S number. The Mustang guide calls its figure an approximate dry capacity that includes the cooler and tubes. The Explorer guide says its figure is only an approximate dry-fill capacity, that some applications vary with cooler size and whether the vehicle has an in-tank cooler, and that the amount and level should be checked by a qualified technician. The difference between the Mustang and Explorer figures is cooler and line volume, not a different gear train. Ford's 2002 Explorer and Mountaineer service manual lists 12.6 quarts (12.0 L) for the 5R55W/S and carries the same warning: capacities are approximate, and the correct level is set by the check procedure, not by the amount of fluid added.

A dry fill means an empty case, converter, cooler and lines. You only see that after an overhaul or a converter replacement. What you'll add in practice:

• Pan and filter service: most of the fluid stays in the converter, cooler and lines. In my bay a 5R55S usually takes back somewhere around 4 to 5 quarts after a pan drop. That's a shop number, not a Ford spec. Measure what you drained and set the final level at the plug. Ford's service-manual draining procedure also has you pull the converter housing access plug and drain the converter through its drain plug, which gets far more old fluid out; Ford requires a new converter drain plug, torqued to 89 lb-in (10 Nm).
• Overhaul with a new or drained converter: have 12 to 13 quarts on hand, prefill the converter as much as you can, and set the level with the procedure below after the first start.
• Auxiliary cooler added: the Ford chart doesn't account for it. Fill by the level plug, never by the chart.

How to check the level without a dipstick

Ford's owner guides don't give an owner procedure for this. The Mustang guide says the fluid should be checked, and added if needed, by an authorized dealer. Both guides say the unit doesn't consume fluid, so the level only needs checking if the transmission slips, shifts slowly or shows a leak. For the shop procedure, ATRA Technical Bulletin 746 (February 2003) lays out the Ford method for the 5R55N, 5R55S and 5R55W. It describes a Fluid Level and Fill Plug assembly in the bottom of the pan, with no dipstick and no filler tube. Here's the sequence from that bulletin:

1. Connect a scan tool and monitor transmission fluid temperature, PID TFT. The fluid needs to be between 80-120°F (27-49°C) when you finish.
2. Start the engine. Idle should be about 650 rpm.
3. Put the selector in Park.
4. With the engine running, get the vehicle on a hoist as close to level as possible.
5. Hold the larger drain plug with a wrench and remove the small center fluid-level plug with a 3/16-inch Allen key.
6. To add fluid, install the fill plug adapter, Ford special tool 307-437, into the center of the drain plug and pump in clean MERCON V. The bulletin uses a Rotunda fluid transporter (307-D465) at no more than 30 psi of shop air, adding one pint at a time.
7. When fluid drains back out, the transmission is full. Let the excess drain and confirm the fluid is still in the 80-120°F window.
8. Reinstall the small center plug. The bulletin's illustration gives 10 Nm (89 lb-in).
9. Move the selector slowly through each range, stopping in each position so the transmission engages.

One caution from Ford's 2002 Explorer/Mountaineer service manual: when using pressurized fill equipment, reduce the pressure to 1 psi. Higher pressure can push fluid out of the vent, and it then shows up as what looks like a leak from the torque converter area. If an Explorer comes back with "converter seal" wetness right after a fluid service, check how it was filled before you pull the transmission.

Why the temperature window matters

ATF expands as it heats. The level plug only reads correctly inside Ford's temperature range, which is why the bulletin starts with the TFT PID instead of "drive it 20 miles." If you pull the plug with the fluid at 170°F after a road test, fluid will run out that belongs in the unit, and you'll leave it low. If you check it stone cold at 50°F, the level reads higher than it will once it's warm, and you'll underfill it. On a lift, a 5R55S at idle can climb out of that window faster than people expect, so watch the PID the whole time and work quickly.

From my own experience, the mistake I see most is a technician who pulls the level plug, sees nothing come out, and adds fluid until it runs, but with the engine off. The procedure is done with the engine running in Park. With the engine off, fluid drains back from the converter and the circuits into the pan and makes the level look higher than it will be once the pump is running.

Low versus high

Low fluid on a 5R55S shows up the way it does on any unit: the pump draws air, line pressure drops, and you get slipping, delayed engagements and heat. Because nobody can check it at home, a slow leak can go a long time without being noticed. An overfilled 5R55S foams, and aerated fluid gives you the same soft, late shifts as a low one. Either way, set the level correctly before you road-test for a shift complaint. A diagnosis done on a unit a quart off is a diagnosis you'll redo.

How often to change it

Ford's 2006 Scheduled Maintenance Guide covers both 5R55S vehicles. On the normal schedule for trucks and SUVs, which includes the Explorer, the automatic transmission fluid and filter are changed at 150,000 miles. On the normal schedule for cars, which includes the Mustang, the fluid is changed at 150,000 miles as well. The routine fluid-level inspections on that schedule only apply to units with a dipstick. A 5R55S doesn't have one, so on a normal schedule nobody looks at its fluid at all unless there's a complaint.

The special operating conditions section of that same guide is the one that fits most of these vehicles. Towing a trailer or using a camper or car-top carrier calls for an ATF change every 30,000 miles, and so does extensive idling or low-speed driving such as delivery, taxi or patrol use. Ford notes that the 30,000-mile change is not required on the 6R60, which is one more reason to confirm which transmission is under the Explorer before you quote the job.

My advice for a 5R55S that has towed anything or seen a lot of stop-and-go: treat 30,000 miles as the interval. A pan drop only changes part of the fluid, so on a unit with dark, oxidized fluid, a second pan service a few hundred miles later gets the fresh-fluid percentage up without machine-flushing a neglected high-mileage unit.

Pan-off service traps on the 5R55S

Don't mix solenoid-body parts between 5R55 versions. Sonnax's 5R55 identification article warns that the solenoid assemblies differ in the base plate and the filter, and that if the base plate or filter is mixed, the unit will lose Reverse, TCC apply and solenoid oil pressure. If the solenoid body comes off during a pan service, the parts that go back on have to match the unit. That's the S or W version, not the older N with its reverse pressure switch.

Read the pan before you clean it. A light gray paste on the magnet is normal wear. Black friction material you can feel between your fingers means clutches are wearing. Brass-colored flakes point to bushing or thrust washer wear. Steel chunks or pieces of a snap ring mean the unit is coming apart, and a fluid change won't save it. That's my own read, not a published chart. It's the same read I use on every Ford rear-drive unit.

Know which complaints fluid won't fix. The 5R55S and 5R55W are known for servo pin bore wear in the case, which is why Sonnax sells a dedicated overdrive/intermediate servo pin bore sleeve kit for them. Fresh fluid can mask that kind of wear for a few weeks, but it won't repair it. If the unit had a shift complaint before the service, plan on a pressure test and a look at the servo bores (our servo pin bore guide covers the test), not a second fluid change.

Quick spec summary

Need parts for this job?

Our 5R55 parts page carries filter and pan gasket kits, the 307-437 style fill adapter, solenoid packs, valve bodies and complete rebuild kits for the Explorer, Mountaineer and Mustang units. Checkout is on site.

FAQ

What transmission fluid does a 5R55S take?

Ford specifies MERCON V for the 5R55S. The 2007 Mustang and 2007 Explorer owner guides both list Motorcraft MERCON V, part XT-5-QM, and the current Motorcraft part numbers are XT-5-QMC (quart) and XT-5-5Q3M (5-quart). Do not confuse it with the 6R60 six-speed in some Explorers, which takes MERCON SP.

How many quarts does a 5R55S hold?

Ford lists an approximate dry-fill capacity of 11.2 L (11.9 quarts) for the 2007 Mustang and 11.7 L (12.4 quarts) for the 2007 Explorer, with the difference coming from cooler and line volume. A pan and filter service takes much less, usually around 4 to 5 quarts in practice, and the final level is always set at the level plug.

Does the 5R55S have a dipstick?

No. Ford's 2007 Mustang guide states that the 5R55S transmission does not have a transmission fluid dipstick. The level is checked at a small plug in the center of the pan drain plug, with the engine running in Park, the vehicle level on a lift, and the fluid at 80-120°F on the scan tool's TFT reading.

How often should 5R55S fluid be changed?

Ford's 2006 Scheduled Maintenance Guide calls for a fluid change at 150,000 miles on the normal schedule, and every 30,000 miles when towing or when the vehicle sees extensive idling or low-speed driving. Most 5R55S Explorers and Mustangs fit one of those severe-service conditions at some point, so 30,000 miles is the practical interval.

Can I use MERCON LV or MERCON SP in a 5R55S?

No. Ford's spec for the 5R55S is MERCON V, and Motorcraft lists MERCON SP, LV, ULV, Type F and CVT applications as places not to use MERCON V because they are different fluids. If LV or SP has been added to a 5R55S, drain it and refill with MERCON V.

Related guides

• Ford 5R55S and 5R55W Transmission Problems
• 5R55S vs 5R55W Differences
• 5R55W and 5R55S Servo Pin Bore Wear
• 5R55 Harsh and Delayed Shifts
• 5R55W P0741 Fix