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The 4.6L Ford engine has been installed in millions of vehicles over the years. It is the engine of the very popular Ford Crown Victoria, Mercury Grand Marquis, and Lincoln Town Car. These engines use plastic intake manifolds and from 1996 through 2001 there was a problem that can leave drivers stranded.  The problem is a sudden cracking of the intake manifold.

The Ford plastic intake problem

The plastic manifold used on these 4.6L engines tend to split across the front, and break in the rear, without warning. Often this will occur with out previous symptoms. Other times a slow coolant loss may precede the failure. When the intake fails, the engine coolant pours out, and the engine quickly overheats.

Problems with the 1996-2001 Ford intake manifold 

The front temperature sensor and rear heater hose connection are also prone to pulling out of the intake. Intake manifold replacement is an expensive and very inconvenient problem but Ford has never recalled the vehicles. Rather, a class action suit against the automaker was quietly settled several years ago. Ford agreed to reimburse some customers for a short while and extended the warranty to seven years from the date of purchase.  The last warranty extensions ended in 2008.

Identifying the problem Ford intake

The new and old style intake manifolds for the 4.6L Ford Engine 

They introduced an improved intake manifold beginning on the 2002 models and this greatly reduces the chances of problems. The new intake has a cast aluminum piece across the front and a redesigned alternator mount.  The new intake manifold has less stress on these key mount areas and a stronger material to support the load.

Why do the Ford intake manifolds crack?

The alternator is mounted to the plastic intake manifold

On the original all-plastic version, Ford braced the rear of the alternator to the intake. The belt pulls heavily on the front of the alternator especially under load. Years of hot and cold cycles combined with the vibration and pull from the alternator can result in the plastic intake splitting. This allows the pressurized engine coolant to flood out, into the rear of the alternator.  Repair involves replacing the old style intake with the new, replacing the coolant and sometimes the alternator. Since the intake is buried under several layers of engine components, this is no small task.

Intake area of the 4.6L Ford engine with the engine cover removed

In some instances the metal threads of the engine temperature sensor and the heater hose nipple also pull out of the intake. The result is the same as with the split plastic: the coolant is loss and the vehicle is disabled.

The most common vehicles to have this problem are Ford, Lincoln and Mercury, built from 1996 through 2001 and having the 4.6 liter engine. We have also seen leakage to a lesser degree on the later models.

Lists of Ford products, with Intake manifolds prone to splitting


Mercury Grand Marquis


Lincoln Town Car


Ford Crown Victoria


Mercury Cougar


Ford Thunderbird


Ford Mustang (some)


Ford Explorer

early 2002

Not really fixed yet? 

The later intakes tend to leak at the front attachment

Ford seems to have addressed the issue of the splitting plastic manifold. They added an aluminum thermostat housing to the front of the intake. In time, this intake also leaks at the seam between the aluminum housing and the plastic intake. Ford does not make replacement gaskets available, without the purchase of a new intake manifold. Often the leak is not visible from the outside and flows into the area under the manifold. In these cases, the symptom is a loss of coolant, with few outside indications.

Replacing the intake manifold 

Replacing the intake manifold is difficult, but can be done with the proper care. We first drain the engine coolant and then remove accessories that bolt to the intake. Remove the bolts and the intake lifts off the cylinder the heads and under the intake. Often they are fine, but replacement is far easier with the intake off. Closely inspect all mounting surfaces for corrosion. Especially check the coolant passages at the front and rear of the engine. Pitting in this area will result in a coolant leak.

Intake manifolds are available though aftermarket sources at a much lower cost than through Ford. The quality is not always good with aftermarket parts, so be sure to closely inspect them before installation.

Check the torque on these bolts, before installing

A common problem with aftermarket intakes is the bolts that pass through the back side and attach the thermostat crossover casting. We always check the torque on these fasteners and often find them loose. Installing the intake without first tightening these bolts requires the removal to correct the problem. The torque on the lower bolts is 18 foot pounds for an original Ford intake.  Aftermarket intakes are not built to the same standard and may crack if tightened to that specification.  We advise using the original equipment part.  The aftermarket supplier of the intake manifold would need to supply specifications for their products.

The thermostat supplied with aftermarket intakes may also be of very low quality. Replacing the supplied thermostat with an original equipment Ford or Motorcraft part, is a very wise precaution.

Torque sequence on intake

We tighten the fastening bolts in a specific pattern. Working out from the center, tightening should alternate from one side to the other and back. We also tighten the bolts in stages, tightening each to 9 foot pounds and then to 18 foot pounds in the same pattern.

If you have a Ford product with the 4.6L engine, AGCO can check it for you. This is also part of our Pre-purchase Inspection, Trip Check, and General Inspection on these vehicles. Don’t be stranded, let AGCO check your vehicle. AGCO, it’s the place to go.

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