Heater fan reduces gas mileage?

[tmckeon88]

Hi all-

I have a '69 Series IIA 88" with the standard 2.25 L and Weber carb set up. The newer style Lucas distributor and a replacement alternator from Motorola; I don't know its history. My question is that when I run my heater, which is a bit of a Frankenstein monster with some generic GM blower motor in it, the lights dim, the radio cuts out and it seems like my gas mileage drops noticeably - like by 30% or more. Is this possible, if the blower motor draws a lot of power and the alternator is not up to the job? It runs/starts/charges OK. It might be that the gas gauge is dropping because its power is being sapped off too, but it seems like the drop is permanent even after I shut the blower off. This winter I've been bundling up for my daily commute and not running the fan because I am trying to stretch my fuel economy.

Any thoughts on what might be happening here? There's been talk about new, higher-output alternators on the boards and I am considering that.

Thanks-

Tom

[LaneRover]

I would check all your connections, if mileage is being significantly reduced I would think that somehow the electrical draw is affecting the spark. Not sure if that is possible but considering that my '88 only gets 1 mpg less when pulling a pretty loaded trailer (albeit small) the heater motor should not effect your mileage by that much. Something is definitely wrong with either a connection, how something is wired or with the blower motor itself.

[siii8873]

the coil increases the voltage by a ratio. If the truck voltage is being drawn down the coil output voltage will be drawn down by the same percent.
If this is the case, not sure by any means, you may have a weak spark poor ignition. I would think if this is happening you should also notice a drastic difference in performance also. Weak spark net result firing poorly low power. Just my 2 cents.

[109 Pretender]

As I read/intrepret the OP I think he's saying the gas gauge needle drops by ~30% after turning on the heater blower. That along with the other clues would probably imply that the blower is tied to existing circuits and is drawing more amperage than the circuit was designed to handle.

I'd check the installation as to where it (heater blower) taps into the harness. The alternator may be weak as well causing the headlamps to dim down when the extra load is placed on the wiring system.

Also find out what the amp draw is on that blower motor. The wiring may need upgrading and/or change how/where the motor is getting power. The orig. circuit is fused and IIRC the heater blower wires are about 16-18ga. More than enough for the factory blower ( is that an oxymoron - calling the LR heater motor a blower? Maybe it should be called a puffer since that's about all they do - 2 speed, slow and slower yet).

Don't waste time not getting this solved - your LR is telling you it's not happy with this situation at all. Wait too long and the "prince" will wake up and smoke the whole harness!

Good Luck!

[jac04]

It's one of the basic Laws of Physics - Conservation of Energy. The blower requires electrical power (energy) to run it. That energy comes from the alternator. The engine turns the alternator to produce that energy. Fuel is consumed by the engine to produce the energy to turn the alternator. The more energy that the alternator needs to put out, the more fuel is consumed by the engine. So, if you have a big heater blower that consumes a lot of energy (which it sounds like you do from your description), then your gas mileage could be significantly impacted.

[superstator]

Yeah, but if a 12v heater is drawing 20 amps, then that's 240 watts. Which is about a third of a horsepower. Even if it's a monster pulling twice that, and the whole system is very inefficient, maye you get to 1.5hp. Yes it'll effect mileage, but not enough to be noticeable compared to everything else going on. Certainly not 30% worth.

I like 109 Pretenders idea that a voltage drop is making the spark less than impressive, or just messing with his fuel gauge.

[tmckeon88]

It might well be messing with the fuel gauge, but the drop seems to stay when I run the car, say, the next day. It might well be that the loss of voltage is making the coil put out a poor spark. It still runs smoothly and everything; I'm not noticing any difference there. But mileage goes down from maybe 16 mpg to 12 mpg. I only run it sparingly, so it's hard to tell exactly what it's doing. I replaced the fan motor about ten years ago and it's been like this every since; I don't do long drives in the winter much so I've gotten used to not using the fan. For the defroster though it's necessary. I'll check to see how it's wired in. I am something of a dunce when it comes to understanding wiring, however.

Thanks for your responses.

Tom