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APR 9, 2020 | By Matt Stone

Here's Why 3.9-Liter V-6's Replaced the 3.8's in Later 4th-Gen Mustangs

Profile of dark gray Mustang in front of dealership

Mustangers know their motors.  They know Windsors from Clevelands, and Bosses and Hi-Pos from anything else. They can tell you every “modular” family V-8 engine that was ever factory installed (or not) in a Mustang.  And the entire alphabet soup of engine option codes from A to C to K, and all the rest, and what years they were offered. Plus all the turbo fours, from Limas to EcoBoosts.

They also know that not all V-6 Mustangs were created equal.

The myriad of six-cylinder Mustang engines seldom get the same love as their V-8 counterparts. There have been a lot of different six-bangers in the Ford Mustang over time – running the gamut from the earliest inline sixes (remember the Sprint 200 I-6?) installed from the beginnings of Mustang production, up to the most recent 3.7-liter Duratec DOHC all-aluminum wonders that happily and faultlessly spool out more than 300 horsepower – mighty impressive for a “base” engine offering, no?

Rear profile of dark gray Mustang in front of dealership

Most will remember that on and off for some years, the standard engine served up in non-GT Mustangs was a 3.8-liter 90-degree V-6 from a Ford engine family called Essex. However did you know that in the waning days of the FOX-4 platformed, fourth-generation Mustang, its Essex V-6 was actually a 3.9-liter? We’d bet not.

Here’s some info to further add to the confusion: Globally, there were two Ford V-6 engine families named Essex; the ones we got in American models are a 90-degree overhead-valve design built in Ford’s Essex Engine Plant in Windsor, Ontario, Canada. The other Essex was a narrower-angle 60-degree architecture V-6 built and served primarily in the UK and other world markets.

Front profile of dark gray Mustang in front of dealership

Why all the V-6 mania? Well, there are several reasons: Of course Ford needed “base” level engines to offer in the Mustang with more oats than naturally aspirated four bangers – remember that thousands of non-GT Mustangs are bought as “first cars” for new teen drivers not needing to be, or not ready to be, pedaling around in a V-8 GT. And most of the Mustangs in rental fleets need a less-costly and cheaper-to-run-and-maintain engine platform than the 5.0-liter (think of those thousands of Mustang convertibles in rental fleets in California, Hawaii, and other sunshine states – virtually all base-engined units).

Another big reason is the need to balance and satisfy the government’s Corporate Average Fuel Economy (CAFÉ) mandates. Even though an updated version of Ford’s original all-iron I-6 from the 60’s remained in production and was offered in the Mustang as late as 1982, its day was pretty much done from a power and efficiency standpoint. That final Mustang straight six, a somewhat archaic evolution of that Sprint 200 I-6 from the original 1965-66 models, finished-up its run beneath Mustang hoods as a 3.3-liter (still about 200 cubic inches) running a single one-barrel carburator while wheezing out 91 horsepower, yet a lot more torque than the even-wheezier 2.3-liter I-4 rated at 88 ponies. Having driven examples of both, we can tell you that the old I-6 was a much better (non V-8, baseline) offering than the I-4, especially in a car with an automatic transmission and the AC running full blast.

Close up front of dark gray Mustang in parking lot

So something modern was more than called for. Ford had developed a line of V-6 engines called Vulcan for use in cars such as the FWD Taurus; they also had the new we’ll call it “Canadian” Essex V-6, which was philosophically similar in that it was also an OHV, 2-valves-per-cylinder V-6, although its accessories were configured for use in RWD cars and trucks.

A common misconception about the Canadian Essex V-6 is that some incorrectly assume it to be a Windsor 302 or a 5.0 with two cylinders sliced out of the middle. This is an easy mistake to make, in that three-fourths of 5.0-liters equals about 3.75 liters of displacement – close enough to 3.8 to give the wrong idea. Another reason this was incorrectly assumed is that other carmakers have done this cylinder extraction deal to create V-6’s out of their V-8 engine designs in the hopes of cost savings by maximizing tooling and parts costs. GM did it a bunch, but Ford did not with the Essex.

Profile of dark gray Mustang in front of dealership

No matter, the Essex 3.8 pushrod engine displaces 232 cubic inches, already a big step up over the old I-6’s 3.3-liters/200 cubes, and features much more advanced combustion chamber, intake and exhaust system design than the old, trusty Sprint 200. The new V-6 is also much lighter, with a more compact cast-iron block and aluminum heads. Some early Essex V-6 installations ran two-barrel carbs, but all of them in Mustangs featured fuel injection. Ford made it the standard base engine for the new SN-95 platform Mustang that bowed for the 1994 model year, at the time rated at 150 horsepower. Along with the Mustang’s MY1999 redesign, the engine got revised intake and other systems updates, cranking the output up to 190 horsepower, with a torque increase to 220 pounds-feet. This V-6 could be backed with a 5-speed manual or 4-speed automatic transmission.

Profile of dark gray Mustang in front of dealership

The Essex 3.8 continued to serve well through the early 2000s, but in 2004, engine production fell short of model sales demands. Simply put, Ford hadn’t planned or produced enough 3.8-liter V-6’s to get through the model 2004 year and needed something to connect the dots between the rest of ‘04 to the all-new Mustang bowing for 2005 (itself destined for a much re-engineered 4.0-liter V-6, now a single-overhead-camshaft version of the 60-degree “Cologne” family V-6). Fortunately, Ford had developed and was producing other versions of the Essex that it could turn to fill in the gap and complete the 04 Mustang model build.

Rear profile of dark gray Mustang in front of dealership

The 3.8 was solid, generally durable and long-lived although it had exhibited head-gasket issues in some models during various years. Ford also engineered and expanded the Essex V-6 lineup into a 3.9-liter version, plus a 4.2 as well. Most of those engines were originally developed for use in Ford and Mercury minivans, and in some F-Series pickups. While it might have been interesting to see the more powerful (up to 205 hp) 4.2-liter Essex in the Mustang, Ford did the logical thing and drummed up pallet-loads of 3.9’s to finish out the ’04 Mustang production run.

Close up front side of dark gray Mustang in parking lot

At 237 cubic inches, the 3.9 was substantively the same piece as the 3.8 save for a slightly longer stroke, now at 3.464 inches. Ford didn’t officially change the reported power outputs over that of the 3.8, although at least one credible independent source quotes 193 horsepower (up from the 3.8’s 190) with 220 pounds-feet of torque. Getting a squeege more power makes sense, given the modest but perhaps meaningful increase in piston stroke and displacement. The 3.9 too could be had with your choice of 5-speed manual or 4-speed automatic transmissions.

Close up of engine under the hood

Mustang V-6 enthusiast Rick Mitchell (who runs a dandy online magazine dedicated to a variety of the Mustang’s V-6 models, at http://www.mustang37.vpweb.com/) has owned and driven 3.8- and 3.9-liter Essex powered Mustangs, both coupes with automatic transmissions, and he advises that the performance is virtually identical between them. Six-cylinder Mustang owners can also check out the Mustang 6 Association (www.mustang6association.org) to mingle with owners of both the inline and V-6 Mustangs over the years.

Close up of engine under the hood

Of course, 2004 was the final year for Essex V-6 (both the 3.8 and 3.9 variants) powered Mustangs, as 2005 brought an all new car and a new base engine, that being the 4.0-liter SOHC Cologne-based Cyclone V-6.  And more recently -- and so far for the foreseeable future -- there are and will be no more six-cylinder powered Mustangs of any sort or form, as the 2.3-liter EcoBoost I-4 has replaced all V-6 offerings as the Mustang’s standard powerplant. Although the V-6 Mustang is gone, the cars and its fans certainly live on in the Ford enthusiast world.

Close up of engine under the hood

Interior close up from driver side of front seat

Close up interior from passenger side of front seat



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