Coolant leak - looks like lower radiator hose
 

This post probably isn't necessary, as I've pretty much discovered the source of a long-standing coolant leak in my 2003 4.4i, but I just wanted to make sure I wasn't overlooking something. I put the car in the air, took off the lower panel, and could quickly spot the origin of my leaking coolant - the lower radiator hose, near where it connects to the radiator, is definitely dripping coolant, as can be pretty clearly seen in this picture:

Attachment 62200

The only reason I'm posting this is that I don't see any obvious cause of the leak - the hose doesn't appear to be split, and there are no visible cracks at the connector to the radiator. But there's no wetness anywhere higher up on the rad hose, or anywhere else for that matter - it all seems to be coming from where the lower rad hose meets the radiator. So, I need to order a new hose, but before I do, is there something else I should look for, or order, that could cause or contribute to the leak? Thanks.

Yeah a crack expansion tank or the radiator itself.

Could it be the coolant level sensor? The o-ring will get old and hard over time.

Not sure about the V8's but the 6 cyl ones have a coolant temperature sender at the lower part of the lower rad hose that can leak.

Thanks; I can't see any hint of wetness anywhere on the radiator, and while there is a bit of "crustiness" on various parts of the expansion tank (so I should go ahead and replace it as well), again there's no sign of fresh liquid, plus the lines coming from the tank don't lead to the area where the coolant is dripping. It looks like the leak is coming from the top of the hose; maybe there's a crack where the sensor's connector is located.

Isn't the coolant level sensor at the bottom of the expansion tank? There's no sign of fresh leakage there - it's all right at the bottom of the lower radiator hose, where it connects to the radiator, but the leak seems to be originating from the hose itself about an inch away from the radiator.

Now that's a real possibility, as it's in the right area. Maybe I should start by replacing the o-ring, and then going from there.

^probably means coolant TEMPERATURE sensor, as the coolant level sensor is not immersed in water. Althoug theoretically water could come out there if the expansion tank had an internal failure...never heard of that ever though.

Yes the o-ring can cause a leak in that area, I have experienced it and a new o-ring fixed it.

Do check your expansion tank as well. These tanks have seams and they can leak from there. I've had this happen to me as well. Since many of these leaks only occur at full operating temp they may be hard to find at idle. Best bet is to clean up the area so they show up easier and check while hot like after a freeway run.

Turns out the coolant temp sensor o-ring was the sole cause of my leak. Once I replaced it, the leak completely stopped. Thanks to the people who pointed this out to me, as replacing the hose wouldn't have done any good.

Unfortunately, while I was under the car working on this, I discovered something more ominous: the valve cover gaskets, which I replaced in December of 2010, are leaking again. AAARRRGGGHH!!! Other that the CV boot replacement, that was the most frustrating job I've ever done on this, or maybe any other, car. There has to be an easier way than the nightmare I went through pulling off those wretched fuel injector retaining clips that I went through last time...