I have an '04 MCS with the OEM Voltmeter and Boost Gauge package. A couple of weeks ago I noticed that the Voltmeter would read 12 volts when running (without AC on) and slowly decrease to 10-11 volts. Then after running the car at highway speeds for 10 minutes or so the gauge would read 14 volts as it normally did. The battery at start seemed to have sufficient cranking power. Over the past few weeks the voltmeter has read right at 12 volts under the same condiitions and the battery has slowly lost cranking power. I charged the battery and it would't take a charge so I replaced it with a Optima 34R thinking that the battery must be the culprit. After installing the battery, it still reads 12 volts on the gauge. Started the car, removed the negative cable from the battery, car continues to run. The new battery is slowly losing cranking power. Any thoughts?

 

Sounds like a bad alternator - if the battery's new and you're not seeing higher than 12V on the gauge, the alternator's not putting out full voltage. As for the car running with the battery out of the circuit, I think once the engine's started, the car will continue to run with as little as 9-11V, so the fact that the car kept running doesn't rule out an underperforming alternator.

 

Test for charge current,
Start car, have someone hold RPM @ 2,000~2,500 RPM, set voltmeter @ 20 VDC, put leads from voltmeter on pos+ and neg- posts, you should see between
14.3~14.5 VDC if the alternator's charging correctly.

Almost forgot, Before testing clean the battery posts and terminals.

 

Thanks Norm! We pulled it in the shop this morning and the readings were 11.9-12.2. The front bumper and inner fender are in the process of being removed to replace the alternator as we speak.

 

Alternator was OK. We removed the alternator and bench tested it with results indicating that the alternator was performing to spec. Back to the MINI, we began a thorough check of all connections and found the positive jump stud, located next to the air box, to have a corroded connection. We cleaned the connection, re-installed the alternator and the system is charging between 14.28 and 14.44 at 2,500 rpm.

It looks like I've found another preventive maintenance item to add to my list.

 

Ah - very good catch. I'm so used to there being a direct connection between the alternator and the battery that I didn't think about extra connections in the path (like the jump stud under the hood).

 

Thanks for the heads up on the + jump start terminal. Not sure I'd have been smart enough to check it. You've got a good crew there.

Where'd you pick up your Optima? Also did you know there is a $25 rebate on them going on now?

 

Bought it at Batteries Plus on Rt23 and I sent in for the $25 rebate.