I am currently dealing with a 2000 ranger 4x4 3.0l v6 its a relatives truck. HE told me that when he stopped at the gas station one day ( this is back during winter) that he noticed a pretty large amount of coolant leaking out of the front of the engine on the passenger side. He quickly added water to the radiator and drove home. not having the money to have it looked at at that time he just drove back and forth to the sotre and added water as needed, truck never over heated. So now for my issue, I cant find a leak, drove the truck for a few miles got it hot etc. no leak, pressure tested no leaks either. the coolant in the resivoir looks brownsh, maybe oil contaminated, there is no coolant in the oil. my qiestion is does anybody have an idea as to whats going on or where to start?, this is mind boggling.

 

The one time overheat could have been a stuck thermostat.
The brown color of the coolant from adding water and not antifreeze , so it's just rust from the water jacket.

 

From his description it seems that the truck didn't overheat and the leak he saw was on the front of the engine, passenger side. First guess I'd make is the timing cover gasket behind and below the water pump, very common on the 3.0s. Sometimes difficult to find because if the leak is really small the heat of the engine block will evaporate it before it becomes obvious. If the thermostat had stuck it more than likely would have overheated. In view of the brownish color of the coolant, maybe the first place to start is a cooling system flush, then a pressure test before refilling with fresh coolant.

 

x2 on the gasket.
but if you don't want to get all crazy tearing stuff apart without knowing. you can do this:
Pick up a black light, or UV light or whatever you call it.
Go to AutoZone or whatever parts store is near you and tell them you want some dye to put in the radiator.
Put the dye in and drive it. after its leaked, take the UV light and shine it under the truck, the dye will turn neon green wherever its leaked from.

 

thanks for the help guys its definitely the timing cover gasket, i spoke to a tech at a local dealer and he said that over time the coolant can become corrosive and sometimes will eat through the timing cover itself. just a little extra info for you that I came across.

Thanks again

 

Green Antifreeze is more corrosive by nature, Its got some kind of Phosphate in it i believe.
As opposed to DexCool or Universal. they don't have that certain chemical that corrodes.