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Dustin Korth

Dustin ... 12/25/2017

1995 Mercury Grand Marquis LS 8 Cyl 4.60L

Preventive Maintenance

Heater draining battery while driving?

I was driving and noticed my lights dimming and the ammeter was really low. I turned off the heater and everything jumped back up to normal. Heater on, everything bogs down, heater off everything runs normal. I left the heater off and made it to destination fine. Next morning, battery was dead, though. Battery/alternator are a year old. Any ideas?

3 Answers


HouseCallAuto

HouseCallAuto 12/26/2017

It is very likely that the alternator is junk. This can be confirmed by attaching the leads from a simple DC voltmeter to the battery. You should read about 14 to 14.5 volts with the engine idling and the voltage should not drop off to the 11 to 12 volt range. You should let the car run for at least 30 minutes while keeping a watch on the voltage because often the voltage drops off as the alternator warms up. If you need to jump the battery to get the car started, shut the engine on the other car after your car starts up but leave the cables attached from the other car while your voltmeter is hooked up.

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Dustin Korth

Dustin Korth 12/26/2017

Jump started and measured voltage at 14.5 volts. Turning the heater on didn't bog it down like before. But if i turned car off, it would not start again.

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HouseCallAuto

HouseCallAuto 12/26/2017

If your voltage with the car running is 14.5 volts and it stays like that, then you shut the car off and immediately get a no crank, then the battery is junk. No so common with a 1 year old battery but I see it happen sometimes. Its charging normal but the battery is not holding the charge. Of course make sure the battery terminals are clean especially between the terminal and the battery posts.

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