Plastic Intake Manifold May Crack Causing Coolant Leak on Mercury Mountaineer

Problem Description and Possible Solution

The Mercury Mountaineer 4.6L V8 model is known for engine overheating, even with normal use, and a coolant leak from the front of the manifold. This will often trigger the check engine light and low engine coolant warning light.

The engine coolant leak is from a factory defect, which causes cracking on the front coolant passage of the intake manifold. In a very short time, this leak will lead to engine overheating issues, especially while the vehicle is idling.   

Between 1999 and 2001, Ford released an updated version of this engine, known as the 'PI' version with a metal coolant passage on the front of the intake manifold, to prevent future issues.

There is no factory authorized repair for the intake manifold, and replacement is required to correct the engine coolant leak and overheating issues.


Problem Data
RepairPal Verified
Average mileage: 131,507 (16,700–209,000)
Electrical & Lights affected: 4.6L V8
8 model years affected: 1998, 1999, 2002, 2003, more2004, 2005, 2006, 2008
84 people reported this problem
Viewing 1 - 20 of 45 comments
Driving down the road, pressed gas pedal and white smoke started coming out back. I pulled over and antifreeze was all over the inside of the engine and hood. Looked and intake manifold where thermostat is housed was completely cracked. It's been leaking for the past month causing antifreeze to cause the ignition coils in cylinder 7 and 8 to go bad. Now it's completely cracked. A shame ford never officially recalled this, poor design that is now costing consumers a hefty bill for a new intake manifold to replace something that wasn't manufactured right to begin with!
I just purchased this vehicle from a private seller. I saw that it was leaking coolant but got a good price on the mountaineer so purchased it anyway. I took it in to get inspected and had every problem listed on this forum. intake manifold was cracked could not find anywhere but dealer cost 700.00 with labor. It also needed rear bearings and hubs replaced and the back emblem has a crack around it. Total cost to repair all problems 1400.00. That bill should go directly to ford because this is a problem that seems to occur on many of the mountaineers.
coolant leak at the thermostat. Replaced intake manifold. $850 incl labor. Shame on Ford. This has been a recurring problem since 1997 at least. Eight years of cracking intake manifolds? Quality is job ZERO.
This problem will cause water to leak into the cylinders and cause them to miss fire making you think there is a problem with the plugs and coils. The car will run horribly but if you look closer you will find that it is in dead the plastic piece under the thermostat housing. It is a real pain. I am still trying to get his fixed and I am sure it is going to cost me a lot of money because it is no longer under warranty.
heater stopped working and brought attention to low coolant. car was also skipping occasionally. when I inspected engine after adding coolant and getting home I found coolant around spark plug. cause of skip. how did the coolant get there? upon further inspection it looked like it was coming from around thermostat.
I thought a gasket maybe. After removing intake manifold I found the problem was not the gasket but a plastic intake that had broken around thermostat. Expensive and time consuming repair. also replaced plugs and the coil pack on the cylinder where the coolant was leaking. continues to run fine now.
I'm purchasing a 2002 mercury mountaineer from a in house financing car dealership and after I drove it for bout a week I noticed the truck started running hot and I finally took it to the shop and they told me that the intake manifold is falling apart because its plastic and its getting to hot and they wanted to charge me around 700 dollars to get it fixed
cracked manifold thermostat housing. Tried to stop the leak with liquid weld--no good. As soon as the car heats up it breaks the welding.
Air con problems took to dealer had a crack after $1600.00 now it's works fine and i wasn't told this was a common problem. I had taken my vehicle once before while vehicle was still under warranty and i was told all was repaired even though it wasn't.
heater wasn't working. it's at garage right now and they said the manifold is cracked and need to get part from the Ford dealer. Part alone is $441. Going to cost over $800 for total repair. HAVE to get it fixed because it's leaking antifreeze all over inside. This vehicle has cost me thousands since i drove it off the lot brand new. Sooooo frustrated right now. It also needs new brakes and hub bearings, again. Plus i just put 4 new tires on it last month. It's worse than a new car payment.
Please tell me who ever thought using PLASTIC in radiators and cooling system was a good idea. Our Mountaineer thermostat housing cracked AFTER replacing the radiator, it still wasn't fixed. Plastic in an engine .. dear lord
One morning I was warming up my 2002 Mercury Mountaineer and noticed a funny smell and a stream of water leaving my drive-way. The temperature gradually began to elevate the typical half marker. I haven't move or driven the truck since. I enjoy the comfort a drivability of this vehicle but over all since I've been in ownership there have been several issues. Ex; Gas needle non-operable, no day time running lights, fog light shortage, door-open alert and interior light, lack of radio volume control, ball joint and rotor issues(right wheel shakes during breaking),Transmission slip due to leak,(trans. pan seal, trans. pan strainer).
Same problem as most others. Notice a miss in one of the cylinders. Took it to the garage to diagnose further. Reported to be the plastic piece of the intake manifold. Really???? A plastic piece on the motor of a car that is constantly heated to high temperatures? Nothing further needs to be said there..
Radiatorwas cracked replaced it and it cracked within 2 days, r placed again ad cracked within 2 days, the crack is always in the same place, at the top where the hose connects
leaked all coolant out in 100+ weather, engine light temperature gauge flashed red off and on while driving. Tech at Joe Cooper Ford, Yukon said it was going to cost $720.00 to replace thermostats and plastic parts.
Starting leaking antifreeze, was told there was a crack on the radiator no need to change yet.. That this problem was common on this model vehicle, now 5months later it started overheating & smoking. Was told by Mechanic, radiator has completely crack special with these below zero temperatures. Now It needs to be replace causing me more than $400 in parts & Labor.

These seems to be a on going issue with these make & model vehicle. With so many complains WHY hasn't it been recalled???