Mysterious coolant leak

[AKForce]

Hello all, long time reader, new poster.

09 Explorer 4.0 SOHC

Our explorer has a coolant leak that we cannot source. There is coolant pooled in several locations directly behind the thermostat housing essentially in a straight line. It does not seem to be coming from the head although we have not ruled it out. The car is not overheating at all, although we have had to add about a gallon of coolant over the last two weeks.

We had two hypotheses and are looking for validation on either or an entirely new concept.

The first is the intake manifold bypass cap. I cannot find for sure if that is a component in the 09, but seems to fit most of the symptoms.

The second relates to the previous owner. The thermostat housing cracked during his tenure and he JB Welded it together. Obviously it cracked later, and we replaced the housing. We later had to replace the radiator and water pump, although we are not sure they are related to the poorly repaired housing, but if they are could there be other stresses in the coolant system that could cause leaks?

Relevant repairs we have done are new thermostat and housing, radiator, water pump, tensioner pulley, top radiator hose.
We thoroughly checked the housing and it is not leaking. We don't think the head is leaking because there appears to be no internal signs of a blown gasket and the coolant is pooled in higher areas than the head. We do not think it is the intake manifold itself because we are not experiencing any other symptoms.

Any help would be thoroughly appreciated. Thanks!

 

[SixPonies]

If you just replaced the thermostat housing with an OEM plastic one, it's highly likely that it's failed/cracked again. I'd suggest purchasing an aluminum t-stat housing. It's a bit more expensive, but it's a one-and-done proposition. It'll never fail again.

Zabteck Performance - Austekk Aluminum Thermostat Housings

 

[AKForce]

If you just replaced the thermostat housing with an OEM plastic one, it's highly likely that it's failed/cracked again. I'd suggest purchasing an aluminum t-stat housing. It's a bit more expensive, but it's a one-and-done proposition. It'll never fail again.

Zabteck Performance - Austekk Aluminum Thermostat Housings

We did replace it with an OEM plastic one- since it was recently replaced I was really hoping that it was not that. I will give the housing another look. Thanks!

 

[AKForce]

So update on the situation...

We let the explorer sit overnight and noticed no coolant leaking so we started suspecting a pressurized leak. Let it warm up and noticed that the top radiator hose was leaking on both ends from poor clamps. Replaced both clamps after cleaning off the connections and then wife drove it to work today. She said that the truck felt like there was more power while driving and did not notice any coolant loss.

When she gets home, know that I know the hose is set, I am going to look at the thermostat housing to make sure that it is not leaking at all.

 

[Havfun]

The housings are notorious leakers and in my case the coolant ended up as you mentioned in the trough between the two cylinder banks behind the thermostat. Sometimes a leak occurs at the lower housing seal where the housing bolts to the manifold. In that case the housing may be good and the seal may be bad. Some folks use RTV at that location. I plan to do that next time. Good luck.

 

[AKForce]

Found the leak... anyone ever seen this or know why it would do this?

 

[Havfun]

It looks to me like someone got frustrated with the crowded corners when installing the housing or the water pump! I don't think those composite materials do this spontaneously!

 

[swshawaii]

^ Agree that's tool user error. Tightly gripped channel locks or vice grips usually spells trouble for plastic hose connectors.