Tuesday, March 27, 2012

How to Fix a Ford 4.6 (Mustang/Crown Victoria/F-150) Thermostat Housing Leak... for 20 cents

Thermostat housing and water outlet on a 1998 Ford Crown Victoria police interceptor- other years similar

Last weekend, I set out to replace the thermostat in a Crown Victoria as part of a routine cooling system service. This should have taken me about five minutes, tops: I've owned more than five Crown Vics in the past few years and have done fairly extensive work on Panther-platform cars. Plus, they aren't exactly mechanically complex machines.

At first, everything went smoothly: I unbolted the water outlet from the intake manifold, replaced the thermostat and gasket, and bolted the outlet back onto the manifold at the Ford spec of 18 ft-lbs. Fired up the car, bled the system, and.... a leak! Coolant was pouring pretty steadily out from the thermostat housing on the intake manifold. Puzzled, I checked the following, which would be the usual suspects for such a leak:
  • The O-ring inside the housing was properly positioned on top of the thermostat.
  • The hose connected to the water outlet was not leaking coolant. This is something to check, because if the hose wears out, it can leak coolant and it will run down the water outlet, simulating a leak from the thermostat housing.
  • The thermostat housing was in great shape, with no pitting, cracks, or defects of any kind. I checked this thoroughly, because the Ford manifolds are well known to crack in various locations.
  • The bolts were indeed torqued down to the proper amount, and they were torqued in equal increments.
Swapping the O-ring for a different one didn't help. Nor did replacing the thermostat again, which I tried out of desperation. I even tried soaking the water outlet in brake cleaner to no avail. By this point, I was very frustrated and about to give up and just RTV the sucker to death (a cardinal sin, in my book).

I was getting more sure that I was going to have to replace the intake manifold. The thermostat housing leak is a relatively well documented issue among 4.6 engines in Crown Vics, Mustangs, and F-150s, and most forum threads end with a "your intake manifold is shot." But my manifold didn't need replacement. Here's how to fix a leaking thermostat housing / water outlet on a Ford 4.6 engine.

I noticed something as I was putting everything away for the night. Both washers on the water outlet bolts were bent significantly. This was probably thanks to whoever replaced the thermostat before: the bolts were WAY too tight, which probably bent the washers as you can see below.

On a hunch, and with a definite attitude of desperation, I found some washers in the garage. I thought that because the original washers were bent, they might cause the torque to be applied in a manner that wouldn't hold the outlet to the housing in the right fashion.

The original washers are built into the bolts, so I just slid the new washers down over the originals. I tightened them down onto the housing in equal increments down to the Ford spec of 18 ft-lbs, started up the car.... no more leaks! I added some UV dye to the coolant and shined a light on the area, still no leaks. 

If your thermostat housing is cracked, pitted, warped, or otherwise messed up, you might be in for a manifold. But if it looks okay and still leaks, give the washers a try! You might be surprised what happens.

    1 comment:

    1. Same problem with my '00 Merc.
      Did you use rubber o-rings, or steel washers?


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