I recently bought a 2003 Lariat which the previous owner told me had a heater issue. Now that I have been driving it I have experienced the issue. When the engine is warmed up it will blow cold air from all vents. Turning automatic off and on will sometimes get it to work or driving it for awhile. When it starts working it works all day. Please help I am in Canada and it is getting colder every day here.

 

Run a self test on the EATC.

http://ww2.justanswer.com/uploads/mu...42619_1121.pdf

 

Thanks for the reply and attachment. I tried to run the self test following the steps in the attachment but it did not respond.

 

I tried it again and it worked. I turned the unit off first - that worked - there were no faults. Yesterday driving to work it was blowing cold air and I noticed while driving the temperature gauge spiked up for a moment and it blew warm air. Then it spiked down and blew cold air again. When at work I checked the heater hoses in to the coil and out. The hose in was a little warm and the one out cold. I filled the antifreeze tank and drove two miles down the road. When I returned the tank had burped out some antifreeze. I talked to the previous owner. He had been losing heat. So he got the heater coil flushed, changed the thermostat, then changed the water pump, then pressure tested the system for a head gasket leak. I am stumped right now.

 

Check the upper radiator hose during a complete engine warmup cycle. It should remain relatively cool until the thermostat opens around 195°. They might have installed the thermostat incorrectly or it may be defective. You might also have an air pocket in the system or a failing water pump.

 

Blend door could be broken.

 

That wouldn't account for the erratic gauge operation.

He has a problem related to the circulation of the coolant.

 

I parked on a steep hill with the radiator cap off and ran the engine for some time. Then I added a gallon of antifreeze. Yesterday morning warming the engine before work. It blew collant out of the radiator cap. I believe the head gasket is blown and the system is being over pressurized and blowing coolant out. There is never a full system so air is circulating around causing erratic heating and erratic gauge operation. Looks like I bought a bad deal.

 

Update on my issue. I wanted to verify that a head gasket had failed before replacing. I got a ford garage to test cylinder pressure to verify, First they tested the coolant pressure which I had not asked for, Then they tested the cylinder compression and all cylinders passed, The mechanic filled the coolant and said the heat was fine. I said take it for a ride which he did for 5 miles and it did not blow coolant out. I took the truck and drove it the same day by the end of the day it blew coolant out again. I spoke to the mechanic and said would the test for combustion gases in the coolant verify that it was a headgasket. He is trying to locate one from a partner garage, I can buy one on amazon. Right now the truck is junk to me. Any comments on what I have experienced or suggestions. Thanks