Clutch Play
I'm having hot and cold problems with my '97 Ford F-150 XLT extended cab pickup. The truck is a two-wheel-drive model with the 5.4L V-8 and automatic transmission. My main problem has to do with apparent overheating and poor air-conditioner function. The secondary problem has to do with cold air coming out when the heater is on. The truck has approximately 125,000 miles on it. After I started noticing the overheating problem, I also noticed coolant on the garage floor.The radiator was worn out, so I installed a new one. I also replaced the upper and lower radiator hoses. That stopped the leaks, but the temp gauge still reads on the hot side when I'm driving around town at low to moderate speeds (usually under 35 mph). During these times, the air conditioner doesn't seem to cool very well, either. When I get out on the freeway, the temperature readings drop and the air conditioner works better. What could this problem be and how does it affect both the truck's cooling system and the air conditioner? The secondary problem was going on long before the overheating, but I just lived with it. Now, I might as well fix that, too. In the winter when I'm just using the heater, I often feel cooler air down by my feet. The heater is definitely on and I get heat out of the upper vents and for the defogger, but there's still a cold draft on my feet. Could this problem be related to the air conditioning and overheating situation? If not, can you suggest something else?
Evan McAllisterM
Canton, Ohio

We'll address your second problem first, because it's less involved. Other '97 Ford F-150 owners have reported similar heater problems. In most cases, the source of the unwanted cold air is an improperly sealing door in the ductwork. These inner doors or flaps are supposed to direct hot or cold air to the desired vents. It's hard to inspect interior components of the HVAC system, so take your truck to your local Ford service department. This should be an easy fix for them. Your primary overheating problem sounds like a defective fan clutch. The problem seems to be speed-related, which means that sufficient airflow is being achieved on the highway, but not at slower speeds. This problem isn't unique to Ford trucks; it can happen to any vehicle equipped with a fan clutch. Like any part, these units wear out with age. Your radiator fan is belt-driven. As a means of saving fuel and reducing engine compartment noise, it has a thermostat-operated clutch. The clutch allows the fan to remain idle until heat demands are sufficient for it to engage. It sounds like you're not getting fan engagement at low speeds and normal through-the-grille airflow isn't moving enough air to the radiator and air conditioner condenser. The fan clutch is filled with a silicone fluid that can leak and render the unit defective. There is also a coiled bimetallic spring on the outside of the fan. You should be able to see this spring when facing the fan assembly. When this spring gets heated, it's supposed to operate an internal mechanism that redirects the silicone within the coupling. When the clutch engages, the fan is activated. This mechanism can fail. The fan clutch should disengage, once it senses that there is enough airflow to maintain proper temperature readings without the fan. It sounds like your fan is permanently disengaged, which can cause your low-speed problems. When the engine is cold and not running, you should be able to easily spin the fan. You can check for signs of leaking fluid with a flashlight and an inspection mirror, but this can be difficult to detect. Take the truck for a testdrive and get it up to normal operating temperatures. Then, park the truck and leave the engine running. Observe the fan. If it isn't rotating or doesn't start running after several minutes of idling, the clutch is probably defective. Turn the engine off. Now try to spin the fan as you did when the engine was cold. A working fan clutch should be more difficult to turn, since it should still be all or partially engaged. If it spins as easily as when cold, that's another indicator of a bad clutch.

A Pain In The Gas
I have an '85 Chevy Suburban two-wheel-drive with a 454ci big-block V-8. I use the 'Burban to tow my ski boat in the summer and my snowmobile trailer in the winter. It's a great tow rig, but its biggest shortcoming is its incredible thirst for gas. Getting 10-12 miles per gallon was annoying when gas cost was $1.25-1.50, but now that $3 gas is a reality, that poor mileage is cramping my recreation budget. I have too much time, money, and energy invested in the truck to just bail out, but I was wondering how much trouble it would be to install a Chevy diesel engine until gas prices drop? I know where there's a totally rusted out '84 K-5 Chevy Blazer with a good-running diesel engine. I can get the whole rig for about $200. Since the Blazer and Suburban are virtually the same vehicle, I figured the swap could be pretty easy. Since I'd have to take the entire Blazer, I'd have all the little parts to make the swap. I could just mothball my big-block until the gas situation improves. Does this sound like a good idea? Are there any special things I need to be aware of when making this kind of swap?
Jim Eckhardt
Boise, Idaho

We've received plenty of letters asking about converting a diesel-powered pickup to gasoline, but yours is the first one wanting to go the other direction. Yes, you could make the swap, but why bother? It's an incredible amount of work just unhooking two engines and reinstalling one. Then you want to reverse the process when gas prices moderate. Unless you value your time at less than a dollar an hour, this swap doesn't add up. Where we live, diesel fuel prices are as high as or higher than premium gas, so your savings would be strictly based on the greater number of miles per gallon. The old 379ci GM diesel isn't any all-star in the first place and one out of a thrashed Blazer could be suspect, so why go to all that trouble? You'd be better off conserving fuel by going on fewer outings or picking the lakes and mountains closest to home.