How far on battery only?

porschenut · 12-25-2006, 06:35 PM

I got stranded tonight when my car slowly died due to a discharged battery. It's almost certainly a failed alternator but I won't be able to do any testing until I get back home tomorrow.

So I'm charging the battery overnight and I'll head home tomorrow. Question: How many miles can I go before the car dies again? Home is about 30 miles away and I will be driving at constant highway speed (3500 RPM or so). Will I make it?

Walt Fricke · 12-25-2006, 07:21 PM

I'd take another battery along, or at least one of those small batteries with jumper cables already attached, to give you a little extra range.

Alas, with electronic fuel injection you are using amps not only to pump the fuel but also to run the injectors and control everything.

I think you ought to be able to make 30 miles if you use no lights, no cabin heat, no windshield wipers, and no radio. But I'm not sure. Our 3.2 twice died on the highway (once at night) due to a failed voltage regulator. In the night time adventure I was able to coax it for about a mile after first it quit. I'd turn off the lights and let it sit a bit. This allowed it to start again and I could go a little ways, even with the lights on, before it quit again. Eventually turning the lights off allowed some more driving.

Regulator failure is insidious - you only know about it by noting that when you turn on the key before starting the car the alternator idiot light DOES NOT come on.

Someone with a better feeling for the amperage draw of the fuel pump and DME/injector/spark system could probably quantify things - these use a quantifiable number of amps per hour, and your battery holds a more or less defined number of those same amps.

Good luck

Walt Fricke

Chuck Moreland · 12-25-2006, 07:31 PM

I once had to drive 300 miles without an alternator. This was a CIS car so a little less power draw.

I brought 1 extra battery and did a swap along the way. I made it home no problem with only that one change. I had to use the headlights the last 30 minutes or so, but didn't use the stereo.

It does matter what size battery you have.

With a good charge on a stock carrera battery, 30 miles should be cake.

LakeCleElum · 12-25-2006, 07:54 PM

I once rode a motorycle 600 miles in the rain (Redding, CA to Seattle) on total loss. I'm sure your P-car won't go that far, but 30 miles should be no problem if you keep your headlight off....

porschenut · 12-25-2006, 08:04 PM

Thanks guys. I have a 1-year-old Optima Red Top. I won't need any accessories or lights as I'll be driving in the daylight, so maybe I'll be okay.

Interesting that you mention the VR, Walt. I replaced my VR last summer, which resolved some annoying symptoms, including headlight flicker and unstable idle. I haven't had any problems at all since the replacement. The rebuilt alternator was installed about 5 years/30,000 miles ago.

dtw · 12-25-2006, 08:08 PM

Drove 60 miles with intermittent use of headlights on a CIS car - the alternator shucked its belt. (NO, it wasn't a 911).

Was pitch dark out but I found an Explorer who let me pull in behind him and 'borrow' his lights. Other than that I used the headlights sporadically and once back in town/off the Interstate. Made it home OK, and even drove to the mechanic the next day, but the battery was junk after that.

Walt Fricke · 12-25-2006, 08:48 PM

Dave (the fellow Coloradoan one):

After episode #1 I replaced the VR myself (wife's Carrera, she usually didn't let me tough it). That lasted only a couple of months, so I had a shop do it just in case I had messed something up. Mechanic said I hadn't, it was simply a bad new replacement part. Aaargh.

Anyway, look to see what, if anything, the idiot light does. If it doesn't come on, the VR is a good suspect (assuming the bulb is good). If it does, the alternator is the prime suspect (as long as the fan belt is intact).

After my adventures I bought a volt meter that plugs into the cig. lighter (with a little stuffing, since Euro lighters are thicker than the US variety). Summit Racing has them, among others. That way I could see what was going on. Scary driving at night through our snow (blowers, lights, WWipers all going suck the voltage down). Good thing to have.

Walt

wilke3169 · 12-26-2006, 04:01 AM

Alternator went out on my '81 Targa. I was on the way to watch PCA Races so I went on. Actually traveled 170 miles with no alternator. Problem was I had 30 more miles to go to get home. Had a new battery brought out and drove home with headlights for those last 30. Great to have a voltage gage when this happens. I knew immediately what was going on.

Kevin

beamonk · 12-26-2006, 04:43 AM

I just did it last night ninety miles with lights on. The faster I went, the charge got low, I pulled over about 30 miles in and let it sit for about ten minutes running with hazards on, I got in it and drove about 3,000 or less the rest of the way. It is hard doing 70 or less in this car, but I made it. We charged it for about 30 minutes before I left. You should be fine.

porschenut · 12-26-2006, 08:02 AM

Yep, I made it home just fine. I'm not sure whether it was fully charged when I left, but it had to have been real close. When I got home, I put a voltmeter on it and it read 12.3 with the engine off. With the engine idling around 1k rpm, it read 11.8, so it's definitely not getting a charge.

I'm taking it down to Storz today to have them decide whether it's the VR or the Alternator. They have a newly rebuilt alternator in the shop now so they can pop it in in no time.

I like the spare battery idea. Gonna give that some thought.

Thanks again to Walt and everyone else for the support.

azasadny · azasadny's Garage

My Odyssey 680MLT battery shows 12.8v with the engine off and it doesn't seem to hold a charge. I'm trickle-charging it at 2amps right now. What should the "normal" voltage be without a load on the battery? Thanks!