I have had a off and on coolant leak for sometime now. It used to only leak when it was really cold out. I've had it in several times and the pressurized the system and found nothing. This weekend I noticed a leak under the van and sure enough it is coolant. It's not cold out. I crawled under the van and I can see where I think it's coming from. However, I have looked to see what this piece is and I can't identify it. I was thinking it was the water pump but I don't think so. The water pumps I have looked at don't have lines attached to it like this unit does. This is on a 2002 E250 5.4L.

 

When hose connections get warm they expand and sometimes enough to not leak even when under pressure.
The secret is to pressure test the system when cold.

 

Well I left it at the repair shop this morning to have them look at it. If they call and say they can't find it, I might tell them to replace the water pump. That is what I really think it is for some reason. I have had it to them several times in the past and they couldn't find it and I'm just fed up with it.