My 2007 F150, 5.4, lost all the coolant the other day. I limped it home about 5 miles, and checked the thermostat after it cooled down. It works. I filled it with water, drove it about 15 miles, and when I got home it took almost a gallon of antifreeze/coolant. It's sat ever since.

I don't see any leaks underneath it. There is a slight coolant smell. No milky looking oil, looks like it was just changed. Please tell me my water pump is going bad, not something major.

 

In one sentence you say it lost all of it's coolant and in the next you say it only took a gallon ?? the system holds almost 4 gallons. where is the coolant smell ?

 

Water pumps have a weep hole that allows the coolant to flow from when the seal or shaft of the water pump fails. It can be sometimes difficult to locate this weep hole (its located on the neck of the water pump shaft housing, usually at the bottom), but with the amount you are loosing, it would be very visual to see that much coolant loss if it were a water pump failure.

If you cannot see any coolant leaks, then its a strong possibilty that you have a blown head gasket. It can blow and allow coolant into the crankcase, as seen with the milky white type oil, or it can blow, allowing the coolant to be burned by a cylinder (or two). This is easily determined by whitish smoke coming from the tailpipe, or by removing the spark plugs, and looking for one (or more on that side) that will be "squeaky clean", as the coolant will become and act like steam when entering a cylinder, and clean it.

Either way, if its a head gasket failure, the head will have to come off, be machined flat, and a new head gasket installed.

 

You didn't read the entire post. I refilled it, let it sit all night, THEN drove 15 miles.

 

Mine did the same thing one day sitting in line at a stop sign.( did not overheat) When I got home it was dumpng coolant which was running down the top of the rubber fan shroud towards the front bumper. I never could locate the leak. I refilled it and it hasn't happened again. I wondered if there was an overtemp blowout valve underneath or a drain valve on bottom of the radiator.

 

Yeah...that's what it said ...it sat all night.