Too Much Overheating
Q:I have a 2001 Dodge Durango with 92,000 miles on it. This summer, it started overheating during a road trip. It's usually okay when I'm driving on a straight road, but the minute I hook a trailer to it or start pulling hills, it overheats! No mechanics have been able to diagnose the reason. I've had the following work performed on it and it still overheats: new heater core, new thermostat (even tried running without one), new water pump, new antifreeze, new radiator cap, and cooling-system power flush. I can drive it about 60 miles max, then the temp gauge rises so much I have to stop and all the water boils out all over the place. There's no water in the oil and no steam is coming out of the tailpipe, so I'm told it's not a head gasket. The fan clutch seems to be fine.
A:There are a bunch of things to check and double-check. Let's start from the front. Be sure there's nothing obstructing airflow through the radiator. Grille ornamentation, a plastic bag pinned to the front of the A/C condenser, a missing air deflector beneath the bumper, or leaf and debris buildup between the radiator and the A/C condenser, can all cut down on the essential airflow through the radiator. Also, you had the coolant-system power flushed, but what did that really accomplish? Even the best job won't clear a severely obstructed radiator. So you should bring the radiator to a fully equipped radiator shop where it can test the radiator's flow rate in gallons per minute. This will determine if the radiator still has the capacity to cool your engine. If 92,000 miles was the first time you checked your antifreeze, there could even be "grunge" partially obstructing the coolant passages within the engine block. High ambient temperatures and load on the powertrain (towing and climbing hills) maxes out a coolant system's capacity. That's why manufacturers offer towing packages with higher-capacity radiators and auxiliary transmission coolers. Is your Durango equipped? No water in the oil and no notable steam out the tailpipe isn't an all-clear on a leaking head gasket. Checking for hydrocarbons inside the coolant system's expansion tank with an exhaust gas analyzer is a more accurate test.
Troubleshooting a Dodge Sending Unit
Q:My 1999 Dodge Durango's gas gauge always reads full. How can I fix it? The auto parts store says the problem is a bad fuse, but I checked all of them. Someone else suggested I'd have to take the gas tank out and look at the float.
A:Fuse? Not likely. There would be additional components out of commission if that were the case. Without going too far into Ohm's law (I = V/R), the basic operation of your fuel gauge is just as it was 40 years ago--a variable resistor attached to a float in the fuel tank. As the float rises with fuel level, sending-unit resistance decreases and the fuel-gauge reading goes up, vice versa as fuel level decreases. But from there it gets more complex. Instead of that variable ground circuit from the fuel-gauge sender going directly to the fuel gauge in the dash, it goes to the PCM, where the data is directed to the electronic instrument cluster and translated to a fuel-gauge reading. Here's something that might help narrow things down. If you can't reach the four-wire electrical connector on top of the fuel tank without dropping the tank, try to locate a larger connector at the frame rail under the left front fender. It should have a black/pink wire going in and a black/tan wire coming out of the cavity marked #1 and a dark blue wire at cavity #4. If you disconnect either one of these and the fuel-gauge reading drops to empty (ignition on)--assuming the tank isn't full of gas--then the problem is at the sending unit in the tank, and the tank has to come out. If the reading doesn't change at all, the problem is elsewhere and requires a technician to track it down. Failures in the tank could include a bad sending-unit resistor, a poor internal electrical connection or the float hanging up, possibly due to a loose baffle within the fuel tank.
Circling the (Battery) Drain
Q:I bought a 2007 Silverado extended-cab LTZ 4x4 with the Z71 option. Two dealerships and General Motors told me there are so many electronics operating all the time the battery will run down if sitting for an extended period. With mine, it only takes about three weeks. Why is no one investigating and reporting on the battery rundown problem with Chevy Silverado trucks?
A:Does your truck use more current while shut down than others? It's possible--a new four-wheel-drive Silverado has more than 25 computers on board. Nowadays, there's a module for almost everything. And yes, there was a battery-drain issue which was corrected by reprogramming the Body Control Module. It was a campaign affecting certain dealer inventory and in-service vehicles. And I have it from a reliable source that the reprogramming did correct the problem as intended. But there are a few other things to look for in your situation. One is the use of any and all aftermarket (or GM-sanctioned) accessories that have been wired into the courtesy-lights circuit. This may prevent that same BCM from powering down, therefore draining the battery dead. The correct testing for a parasitic draw (current used from the battery while everything is off) is a must to be sure it's not excessive. It's also important that the battery itself be tested accurately, or you may wind up with a borderline unit that drives you crazy. GM has gone as far as stressing how important it is to have the battery cables properly clamped to the battery. Last, but not least, you may very well be letting it sit too long, just like everybody's been telling you. General Motors notes that letting a vehicle sit for 30 days or driving only short distances once a week is abnormal use and can kill a battery. An engine has to run for long periods of time, above 1000 rpm, for the alternator to fully charge a battery. So going out in the garage once in a while and running it for a few minutes won't really help. Sounds like your truck is somewhere in the middle of all that. If that's the case, your choices are to alter your driving schedule, disconnect the battery when parked, or use a slow-charger specifically designed for maintaining a vehicle's battery charge while in storage.