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400M -> RE: 1998 Ranger Heater Problem (12/26/2007 2:15:23 PM)
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Run the engine (drive the truck somewhere if you don't want to just sit and idle) long enough to where the engine SHOULD be up to operating temperature. Open the hood and feel the upper radiator hose. That engine should run at about 195 degrees, and that hose will be VERY warm to the touch if the engine is indeed running at the correct temp.
(If you do this sort of thing long enough, you will develop a "feel" for how hot it should feel to you...but as a basic rule, if you grab the hose and can hold it comfortably, the engine is probably NOT at 180 or more degrees.)
Next, feel both heater hoses. Grab one first and get a "feel" for how hot it is, then grab the other and do the same thing. They should BOTH be hot, and close to the same temperature, although it is normal for the return side to be a little cooler than the inlet.
If one heater hose is much cooler than the other, then that usually means there is either a restriction in the core, or a heater control valve somewhere keeping coolant flow from running through your heater core.
If the hoses are all hot and you're still getting no heat inside the cab, check for air leaks. If the heater box is damaged and enough cold air can get in, then the heater won't be able to keep up with the drop in temperature. In such a case, you may notice that the heater blows fairly warm when the truck is standing still, but blows colder the faster you drive. While working at the Ford dealer, an F150 came in with this condition and the firewall was mangled from a previous accident, letting cold air enter just below the heater box. The truck needed some firewall repairs and the heater box re-installed, and it worked fine.
In another case, with a V8 E150, the impeller on the water pump was loose on the shaft, so the water pump appeared to be turning, but no coolant was circulating! This, of course caused an overheating condition that the owner couldn't figure out, but a new water pump solved the problem!
These are just a few quick ideas off the top of my head for ya...there could always be more to it, but you want to start troubleshooting the problem rather than just "throwing parts at" the problem...to insure you get it fixed right.
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