philipswanson

Trouble is, there are other places that are much more prone to water leaks than the thermostat housing. Probably a big waste of $$.

jimkaray

The issue is that it is not prone to leaking it is prone to complete failure.
If you have a list of components on these cars that are prone to leaks that would be a helpful addition to the discussion since I'm not aware of any.

philipswanson

The biggest item prone to leakage are those crappy stock head gaskets from scrubbing and compression and cooling leaving gaps. I have also seen direct casting leaks due to impurities in the casting materials used in the heads.
Best fix, load it up with stop leak. When it breaks, install a 5.0. Changing the thermostat housing is like rearranging chairs on the Titanic.

JimC

On the 4.0 the plastic thermostat housing is the point of failure in almost every case. Very few head gasket failures; rare to see that on any forum (and yes, I know that you had a head gasket failure - again, a rare occurrence). My 2006 4.0 is over 245,000 miles and the only failure was the thermostat housing. I was still racing it almost every weekend up until I sold it with 203,000 miles on it and running mid 12's; had nitrous on that car for 2 years, then at 90,000 miles pulled the nitrous and put the Xcharger Xtreme on it. Never had a head gasket problem throwing 15lbs of boost at it.

philipswanson

No head gasket failure is very common on the 4.0. I know, I am shopping for a replacement pair of heads since these are warped beyond repair. Hard to find because many have had the same problem. My head machinist tells me he sees at least one a week show up for pressure testing. 99% that fail and are too far gone, just like mine. The thermostat failure doesn't top the list. You want to beat it, buy a 5.0 crate motor from Ford Motorsport and dump that crappy Mazda motor.

JimC

You had a failure, but that doesn't change the fact that it is very rare to see a head gasket failure on the 4.0. Your experience doesn't make it a "very common" failure.

Search the forums and you won't find many head gasket failures. You will find many threads, across all forums, regarding the failing thermostat housing. The head gasket just isn't anywhere near as common. Your head machinist may be telling you he sees at least one a week for pressure testing - but that isn't head gasket failure and they are probably coming in for pressure testing to find the leak and discovering it is the plastic thermostat housing when they pressure test it.

And you've had your 2007 since April 2016? The people here who are telling you that the plastic thermostat housing is the most common failure have been working on the 4.0 or driving them since 2005. Lot of years of experience with the platform.

Stangbass

You're saying that the head gasket is the biggest item prone to leak, when in your own post you said it was a radiator seamed that caused your car to lose coolant, which in turn caused your car to overheat, which in turn caused your issue.

You've also said that your heads warped. I don't know of any head gaskets that will hold a seal on an engine that has warped cylinder heads. I don't care what materials the block and head are made from, if the car runs hot enough to warp the heads you are going to get milkshake oil and eventually kill the engine.

Your problem was your car ran hot. This was because you lost coolant, which was because of a split radiator seam. If your radiator seam held intact, you would not have lost coolant, and your car would not have run hot, and your head gasket and cylinder heads would have been unaffected.

I've had my 4.0 for nearly 7 years and am a member of several mustang forums. The reoccurring failure point on this engine's cooling system has been the plastic t-stat housing. I see 2-3 threads a year about it.

The cooling system on the 4.0l mustang is more than adequate, to keep the engine's cylinder heads and head gasket in working order for the duration of the engines life.

dust180

If we could get them down to even $100 then im in. Just bought a 06, and on the drive home (bought it several hours away from where I live and drove it home) the plastic housing split at the seam. Luckly it happened in a parking lot while we were eating so it never overheated thankfully. (noticed a puddle under the car) And there was a advance auto conveniently located across the road so zipped it up with a dorman replacement and drove on home. Sucks it failed but I couldnt have asked for a better way for it to fail lol

philipswanson

If it was that big of a problem, Ford woulda come out with a service change or at the very least, an improved housing. If you check out Ford, they may have even improved that original thermostat housing. If it is as big a problem as you think, your Ford dealer must know all about it. Talk to the service department before wasting over 160 bucks! In recent years, different formulas have been used in plastics to make them much more heat resistant. Not sure about this application tho.

Phil Swanson

KELVIC

I'm in, put me down for one!