A I'd be looking for electrons. Somehow, while the vehicle is parked, electrons are escaping from the battery. When enough of 'em get away, well, the few remaining can't carry the load of starting the car.
A more professional description of this problem is "parasitic loss." Personally, I like "escaped electrons" better -- doesn't sound so creepy. Apparently, an electrical circuit in the car is drawing excess current when the ignition is off. Normal parasitic loss is in the range of 50 milliamps or less, to keep the computer systems and memory settings alive. This minor loss would take several weeks to drag down a good battery and prevent the car from starting.
To find the excess parasitic loss, a shop can connect an ammeter to measure current flow from the battery with everything turned off. Unplug each fuse and relay -- one at a time -- to find the circuit drawing too much current. My homemade ammeter is an old tail light lamp with wires soldered to it. I disconnect one of the battery cables and connect my ammeter in series, meaning all the current flowing from the battery goes through the lamp. Normal parasitic loss won't illuminate the lamp; there's just not enough current flow. But a significant loss will cause the lamp to at least glow. As you pull fuses and relays, when the lamp goes out you've found the circuit causing the excess electron loss.
Also, make sure to have the alternator's output tested to make sure it's keeping the battery fully charged.
Q I have a '95 Dodge Ram 1500 with the 318-cubic-inch V8 engine. When it gets below 35 degrees at night, the starter grinds a couple of times before it engages and starts the engine. It's like the starter is spinning before engaging. I've replaced two starter relays and two batteries, and the battery cables are good. What am I missing?
A Here's the way I would troubleshoot this problem. On a colder morning when you know this will happen, connect a voltmeter to the starter's (+) terminal and ground. Check the voltage that is reaching the starter as you crank the engine. If the voltage stays above 10 volts, the problem is in the starter. Perhaps the starter pinion shaft is rusty or gummed up with grease or oil and not sliding cleanly into engagement with the flywheel/flexplate. Flushing with Deep Creep may resolve this issue. Another possibility: The starter's clutch is slipping. A replacement starter would eliminate both of these possibilities.
If the voltmeter shows battery voltage dropping below the 10-volt level, check for high resistance in the start circuit from battery to relay to solenoid to starter motor, and the ground connection between the drivetrain and chassis.Motoring note
In response to the question of how to rid a vehicle of skunk smell [Motoring, Sept. 24], James Cappuccilli shared his technique. "I have always had success with charcoal briquettes (non-self-lighting type). I spread them out to get as much surface area as possible. Sometimes in less than 20 minutes the briquettes get replaced with fresh ones. This exchange may go on for quite some time, but it has worked wonders for me. Afterward when everything is smelling just peachy I have a barbecue after airing out the used briquettes."
Great idea -- but I won't ask what he's cooking!