Carburetor fan possibly drains battery below 12v - ever happen to anyone else?

Dishy

Daily Driver
The 0.07 reading is on the 20kOhm range. So it's 0.07 kOhm or 70 Ohm. The 200 Ohm range is reading over range so you have at least 200 Ohms in the circuit. As far as your alternator is concerned over 200 Ohms is the same as not connected. Was this measured from the alternator big lug to the battery +ve terminal? If it was from the alternator to the battery +ve terminal then you have an open connection somewhere between the two.

If you have an open connection between battery and alternator, but you can still start the car then the good news is the open connection is probably between the starter and the alternator. There should be a fairly large wire running from the alternator to the starter around the passenger side of the engine bay. Follow this wire till you find your open connection.

The other reason to check this wire is your alternator was recently changed. It's amazing how often new faults start in the last part of the car touched.

Dishy
 

Dishy

Daily Driver
Also the +ve battery terminal, starter and alternator are all a high current un-fused circuit. Disconnect your battery before doing anything. Accidentally touching another part of the car with the edge of a test lead/alligator clip is too easy to do even when you try not to.
 

ng_randolph

Bjorn H
There should be a fairly large wire running from the alternator to the starter around the passenger side of the engine bay. Follow this wire till you find your open connection.

The other reason to check this wire is your alternator was recently changed. It's amazing how often new faults start in the last part of the car touched.

Dishy
The starter was recently changed as well, so double points for your "last part touched" rule.
 
The 0.07 reading is on the 20kOhm range. So it's 0.07 kOhm or 70 Ohm. The 200 Ohm range is reading over range so you have at least 200 Ohms in the circuit. As far as your alternator is concerned over 200 Ohms is the same as not connected. Was this measured from the alternator big lug to the battery +ve terminal? If it was from the alternator to the battery +ve terminal then you have an open connection somewhere between the two.

If you have an open connection between battery and alternator, but you can still start the car then the good news is the open connection is probably between the starter and the alternator. There should be a fairly large wire running from the alternator to the starter around the passenger side of the engine bay. Follow this wire till you find your open connection.

The other reason to check this wire is your alternator was recently changed. It's amazing how often new faults start in the last part of the car touched.

Dishy
Good catch. I thought the whole reason to redo the test was to use the 200 ohm range instead of the 20K range so I didn't even look. No way it's going to work with 70 ohms unless we're talking milliamps.
 

tvmaster

True Classic
Good catch. I thought the whole reason to redo the test was to use the 200 ohm range instead of the 20K range so I didn't even look. No way it's going to work with 70 ohms unless we're talking milliamps.
Yup, that's why I posted both photos, for comparative interpretation. Since the starter's being replaced next week, hopefully all will be revealed. I can still charge the battery to 12.56volts.
 

tvmaster

True Classic
Finally, the alternator has been replaced, as it had gone bad.
After running 40 minutes at 70mph, shut the car down, and started recording the on-off times of the carb blower fan.
In 45 minutes, the blower came on and off approx 10 times, running from over one minute, down to 20 seconds in the final run.
In total, the fan ran 5:30, with intervals between two and seven minutes, when it finally shut down for good.
 

LarryC

Curator of #10105275
Five minutes is not too long at all for a hot day. It this for a cool day, then that is a bit long, but not outrageous. However, turning on and off so frequently is a little anomalous. Have you changed the thermostatic electroswitch? Seems a bit sensitive. If you look at my chart for a very hot day, it stays on for a good 12 minutes with maybe one turn on-off cycle, very short, after that.
 

tvmaster

True Classic
Five minutes is not too long at all for a hot day. It this for a cool day, then that is a bit long, but not outrageous. However, turning on and off so frequently is a little anomalous. Have you changed the thermostatic electroswitch? Seems a bit sensitive. If you look at my chart for a very hot day, it stays on for a good 12 minutes with maybe one turn on-off cycle, very short, after that.
I've thought about changing the switch out - interesting that mine cycles on and off, for short bursts - and yours stays on for such a long time. Outdoor ambient temp yesterday was high 60's
 

tvmaster

True Classic
Sounds like your thermo switch has less hysteresis than the one LarryC has.
lol. Had to look that one up. Good one. As The Beach Bums sang about in 'Upholstery', "Carburetors man, that's what life is all about..."

Next MWB order, I’ll grab a backup thermo blower switch.
 
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