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

This by itself is a problem. If the battery is showing 11.85V after 6 miles of driving (and clearly, the car was able to start 6 mils ago) there is a problem with your charging system.
Interesting chart. Judging from the data, it looks like the thermoswitch is set for around 140F.
Yup, 60c, which is right in the range of my earlier post. Think I’ll do the kitchen test when I get time…
 
I've posted this a few times, but it is always a useful reminder of how the cycle works. This was a series of temperature readings at the base of the carb on a very hot day after the fan started. Incidentally, the starting temperature was well over 200°. And the temperature of a nearby alternator bracket was 240°. This is why we have water cooling jackets inside the engine.
Any idea why the blower might still be running an hour after shutting the engine off? Most say 5-10 minutes is all that’s needed…
 
Sure is - mounted underneath one of the rear carb-to-manifold bolts. Controls a relay that switches the fan on.
Question: is there supposed to be a duct/hose between the left, outside, lower air vent and the blower? Also, in the manual I see clamps on the paper hose between the blower and air cleaner. No clamps on mine. Is it possible my connection either isn’t sealed, or needs outside air to function properly? Maybe my blower fan isn‘t stopping because it’s not cooling properly?
 
Question: is there supposed to be a duct/hose between the left, outside, lower air vent and the blower? Also, in the manual I see clamps on the paper hose between the blower and air cleaner. No clamps on mine. Is it possible my connection either isn’t sealed, or needs outside air to function properly? Maybe my blower fan isn‘t stopping because it’s not cooling properly?
No. There is no hose from the outside vent duct to the blower fan, only from the fan to the air cleaner base. And unless your hose is "so loose" that it's falling off at one end or the other...it's highly unlikely that's what's causing your fan to run excessively.
 
No. There is no hose from the outside vent duct to the blower fan, only from the fan to the air cleaner base. And unless your hose is "so loose" that it's falling off at one end or the other...it's highly unlikely that's what's causing your fan to run excessively.
ok, good news. thanks.
 
The fan gets outside air from the hole on the left side of the engine compartment that it is butted up to. There is a flexible hose that connects the blower to the plastic duct that blows air on the carb. Does your car have the plastic duct. If not, the blown air may not be getting to the right spot.
 
Any idea why the blower might still be running an hour after shutting the engine off? Most say 5-10 minutes is all that’s needed…
The horizontal axis is in minute and seconds from start. So it ran, and on a very hot day I will reiterate, for just over ten minutes The manual says that it turns on when the temperature exceeds 58 - 62 C (135 -144 F) and shuts off when the temperature drops below 48 - 52 C (118 - 126 F). The fact that it does not run during engine operation is probably more related to the strong cooling of the throttle body by all the vaporized gas and the convective work done by all the air rushing through there when running.
 
The fan gets outside air from the hole on the left side of the engine compartment that it is butted up to. There is a flexible hose that connects the blower to the plastic duct that blows air on the carb. Does your car have the plastic duct. If not, the blown air may not be getting to the right spot.
Yes sir, duct in place, but no clamps on paper hose. Maybe air’s escaping…
 
Ah - yes, good point. I had missed that the stall happened after a good long run that should have recharged the battery. Check the voltage across the battery terminals when the engine is running and turning 2500 or 3000 RPMs.... should be high enough to charge.
Hi again - so I just clipped my meter to the battery, got in, fired 'er up, and..... even at 3k rpm, couldn't get the meter above 12.12 volts.
That doesn't seem high enough for a 61amp alternator, does it? For that matter, that number stayed pretty consistent from just below 1k all the way up to 3k. The battery read 12.40 volts when I started the car.
I was under the impression a decent charging level was up in the high 12's, low 13 volt area. Of course, nothing electric was turned on.
Thoughts?
 
Hi again - so I just clipped my meter to the battery, got in, fired 'er up, and..... even at 3k rpm, couldn't get the meter above 12.12 volts.
That doesn't seem high enough for a 61amp alternator, does it? For that matter, that number stayed pretty consistent from just below 1k all the way up to 3k. The battery read 12.40 volts when I started the car.
I was under the impression a decent charging level was up in the high 12's, low 13 volt area. Of course, nothing electric was turned on.
Thoughts?
Should show right around 13.7v on a healthy system, and it doesn't take 2000-3000 rpm for that output. If the alternator was just replaced make sure the belt tension is correct. If ok then the alternator itself or something related to the installation has gone off the rails.
 
You might want to measure the voltage right at the alternator to see if it is the problem or the interconnect to the battery.
 
Should show right around 13.7v on a healthy system, and it doesn't take 2000-3000 rpm for that output. If the alternator was just replaced make sure the belt tension is correct. If ok then the alternator itself or something related to the installation has gone off the rails.
Any chance a troubled battery would be responsible in any way? I'm thinking not, since I can charge it up to 12.87 with my charger. And in a couple of days it trickles down to where it was today before testing; 12.4volts. Any suggestions on how 'I' could check the alternator, with nothing but a simple multimeter?
 
Any chance a troubled battery would be responsible in any way? I'm thinking not, since I can charge it up to 12.87 with my charger. And in a couple of days it trickles down to where it was today before testing; 12.4volts. Any suggestions on how 'I' could check the alternator, with nothing but a simple multimeter?
The open circuit voltage of a 100% charged lead acid battery is typically in the 12.9 - 13.2 range so the voltage is about right. You can check the battery condition with a hydrometer. They are under $10 at most auto stores. Charge it first.

Your multimeter should be fine for checking the alternator. Just put it on the correct DC voltage range, connect the ground lead to chassis ground, and the hot lead to the stud on the back of the alternator with a big wire going to the starter. Some alternators have a removable plastic cap on the terminal to help keep it from getting shorted when you drop a wrench down there. Remember, the other end is connected to the battery so power is there even with the engine off. It would be best to use some clip leads so you don't have to keep your hand in there with the engine running.
 
Thanks. At this point, I thought I was in the clear, but it appears my lack of knowledge doing my own work is apparently costing me at the hands of at least one ‘expert’, who’s now put in a crap starter, and what looks like is also a crap alternator…,
 
Thanks. At this point, I thought I was in the clear, but it appears my lack of knowledge doing my own work is apparently costing me at the hands of at least one ‘expert’, who’s now put in a crap starter, and what looks like is also a crap alternator…,
Maybe, maybe not. Check the voltage at the output stud as @dllubin suggested and double check that when the key is in the "run" position the "G" is lit in the cluster. If the bulb burns out there is no continuity for the exciter circuit.

IMG_3081.jpg

 
Thanks. G is solid and working. And it doesn’t flicker like it did before under strain. But I should have been smart enough to have him test how much charging power was being produced at time of install, but I didnt. I’m one of those old guys who trust engineers who appear to be smarter than I. My old-fashioned habits are costing me. Cest la vie.
 
Thanks. G is solid and working. And it doesn’t flicker like it did before under strain. But I should have been smart enough to have him test how much charging power was being produced at time of install, but I didnt. I’m one of those old guys who trust engineers who appear to be smarter than I. My old-fashioned habits are costing me. Cest la vie.
Good thing you have the multimeter. I would not accuse the guy that put in the alternator until you get the voltage readings. There are a few other things that can go wrong between the alternator and battery in an X.
 
Good thing you have the multimeter. I would not accuse the guy that put in the alternator until you get the voltage readings. There are a few other things that can go wrong between the alternator and battery in an X.
Maybe. We‘ll see - and it may not be all his fault, he may just need to find a better parts distributor. How many things, by the way?
 
It's possible that the W-D mechanics may not have entirely understood the carb fan functions and consequently may not have installed the carb fan's temp switch in the correct location.

You should probably ask someone with a '74, or perhaps any year with a stock carb fan setup, to post a pic of where their carb fan temp switch is mounted. I'm guessing it's been mounted somewhere where it has no trouble getting hot but not where it can get cooled by the fan. Since the purpose of the fan system is to cool the carb, I would think the stock location for the temp switch would be within inches of the carb.
 
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