Coolant leaking from heater hose above thermostat housing

[Lukas2009]

The little heater hose which sits on the top of the thermostat housing was leaking at the bottom of the hose.
I inspected the housing which had been replaced last year. Seems to be ok. No coolant to find around the housing or the sealings. Coolant can be only found at the top of the housing.
So I replaced the hose and the clamps, but had to notice that it is still leaking like before.
Now I am thinking about what could be the reason for this. Could it be that the pressure in the cooling and heating system is too high and the heater hose acts like a kind of valve to release pressure?
My mechanic wants to use stronger clamps to solve the problem, but I am afraid that than the system could start leaking elsewhere in my car.
I already use the 16 psi radiator cap for years.

 

[BrooklynBay]

Connect a cooling system pressure tester to find the exact location of the leak. It could be the thermostat gasket or maybe the hose has a pin hole.

 

[gdgiordano]

Connect a cooling system pressure tester to find the exact location of the leak. It could be the thermostat gasket or maybe the hose has a pin hole.

My money is on the hose. Those thermostats fail further down usually. Make sure the clam is far enough down on the attachment point. I have noticed these clamps like to slide up the hoses.

 

[Lukas2009]

The mechanic already used a pressure tester and identified the bottom of the hose as the location of the leak.
Then he changed the hose with a new one (Motorcraft) and after that he didn't make another pressure test.
I took the car home and the next day I saw that it is still leaking at the same location.
No coolant around the thermostat housing. Only at the top around the lower end of the hose.
On the image above you can see that the old clam was sitting in the right position.

Could it be that the attachment point at the thermostat housing has a crack?

 

[swshawaii]

I wouldn't rule out the lower t-stat housing. Coolant leaks have the tendency of settling on top of the housing. If it was replaced last year with the aftermarket Dorman housing it's even even less of a surprise. Here's two "seamless" aluminum options.

Engine Coolant Thermostat-Therm 190 MOTORCRAFT RT-1220 | eBay

02-2010 Explorer Mountaineer Aluminum Thermostat Housing Kit | eBay

 

[Lukas2009]

Last year the thermostat housing had been replaced with a complete (plastic) Motorcraft thermostat housing (upper and lower), including thermostat, sensor and o-rings. It had been modified by me. As you can see at the picture below, now there are bolts and nuts that press the layers together, instead of only bolts that in my opinion normally tear the layers apart.

And on my table there is already laying a brand new Motorcraft RT1220 aluminium thermostat housing kit, which I ordered together with the new hose (Motorcraft KH391) a few weeks ago when the leaking started.

 

[katsov]

I would say clamp, hose or, like you suggested, the upper part of the housing where hose connects.

 

[katsov]

Is it dry everywhere else? It's not running down the length of the hose and pooling at the bottom there?

 

[Lukas2009]

gdgiordano meant above, that it could be that the hose clamp could be not enough down.
So I went to my car and had a look. Hm, could be he is right. The mechanic could have fixed it a little bit too high ...
I lowered the clamp about 3 mm, cleaned and dried everything. Tomorrow I will drive some miles and will see what happens.

@katsov: It's dry everywhere else and nothing running down the hose.

 

[BrooklynBay]

You said that the mechanic pressure tested the old hose. Did he pressure test the new hose?

 

[Lukas2009]

No, unfortunately not. That was my first question when I went back to him. He was pretty sure, that the leaky hose was the reason for the leaking and that replacing it would solve the problem.
He wants to make a new pressure test tomorrow. In the meantime I lowered the hose clamp and today I will make a test drive.

 

[rsm48]

Did lowering fix leak?

 

[Lukas2009]

After a pressure test it looks like the reason is the o-ring of the temperature sensor which causes the leaking.
The complete sensor had been replaced together with the thermostat housing two years ago, so I am surprised that the sensor already is leaking.
I have to say that it is a third party sensor.

 

[gdgiordano]

After a pressure test it looks like the reason is the o-ring of the temperature sensor which causes the leaking.
The complete sensor had been replaced together with the thermostat housing two years ago, so I am surprised that the sensor already is leaking.
I have to say that it is a third party sensor.

Dang. You might be able to change the o ring!

 

[Lukas2009]

It's much easier to buy a new sensor with o-ring instead of searching for the single o-ring.
You will not get the o-ring as a single spare part and nobody knows its exact measurements.

I had already bought Ford's metal thermostat housing kit, which includes a new sensor.
But I couldn't use this sensor because it's different to the old one and will be screwed into the metal housing.

 

[Mitchs07explorer]

It's much easier to buy a new sensor with o-ring instead of searching for the single o-ring.
You will not get the o-ring it as a single spare part and nobody knows its exact measurements.

I had already bought Ford's metal thermostat housing kit, which includes a new sensor.
But I couldn't use this sensor because it's different to the old one and will be screwed into the metal housing.

I went to Lowes to find a 9/16 O.D. X 3/8 I.D. X 3/32" Worked perfect. I bought an OEM brand sensor and the O ring was too fat. I cut if off and used the size above and it's worked for almost 2 years now.

 

[Mart1n]

That's great no need to replace perfectly good working parts for a simple O ring failure...