Radiator fan drag and MPG

[nissanh]

I think I found out what dropped my MPG from 20 - 21.5 to 17.5 MPG.

In 2011 I installed two 12 inch electric fans in front of the AC condenser in Las Vegas NV. I had a big load in the truck and was heading to Louisiana. MPG was so bad but due to the load I didn't worry much. Since then I get 17 MPG even with cruse at 65 MPH or 70 MPH. Replaced Fuel-to-air ratio sensor, spark plugs, wires, air filters fuel filters, TPS, fuel injector cleaners (gumout about 6-7 times) and yet, no improvement.

Was talking with a friend in Australia and his prado 5vzfe gets great mileage and said no fans in front of the AC condenser. I then took both fans off and drove about 15 miles in the city with AC and I did not see a change in the fuel gauge! (I usually see a significant drop in the gauge on other times).

Engine fan usually have a heavy drag on the engine and a blocked/hindered flow may cause a big drag. I think the fans were causing a hindrance to the smooth air flow.

I am yet to explore more but wanted to share with others.

 

[3bears]

I don't see how electric fans would hurt mpg, are you also still running the stock fan and fan clutch ?
nor blocking air flow hurt mpg unless the reduced air flow makes it run hot, thus inefficient
I suspect other things, how about your O2 sensor ?

side note, not a yota, but my chevy truck, I saw an increase in mpg by getting rid of the ac compressor and getting rid of the fan clutch and installing a electric fan.

 

[SpidermanGeek]

I'd kill to get 17.5 MPG. lol.

 

[absalom]

Watching fuel gauge for change has to be the absolute least scientific way to track actual mileage.

If you really want to check mileage, fill up your tank at 75% flow rate, until it clicks just once. Drive 150+ miles. Refill using same method. Calculate and report back.

I do however recall an article recently debunking the benefits of electric fans over mechanical fans. Remember, engines are designed to run at a certain temperature, not too cold or too hot. What was the reason for installing the fans in the first place? Were you overheating? Were the fans hooked up through the fan controller and thermostat or were they just manually controlled by you?

 

[gamefreakgc]

Electric fans will save MPG's over a stock fan because of the reduce drag on the engine. The fan is ran by the engine via pulleys so the air resistance create drag on the engine (just like running the A/C does since it's running the compressor) so removing it and putting in electric fans will net you better MPG's. Electricity is free via the alternator but mechanical power comes at a cost. It's not a huge difference though, so before everyone ditches their fans and puts in electric ones it's hardly noticeable.

It's not uncommon for those with rock crawlers to install electric fans for increased air flow at low speeds, since the engine doesn't produce enough RPM's and fan speed to cool off the engine.

 

[02SE]

Watching fuel gauge for change has to be the absolute least scientific way to track actual mileage.

If you really want to check mileage, fill up your tank at 75% flow rate, until it clicks just once. Drive 150+ miles. Refill using same method At the same gas station pump. Calculate and report back.

My addendum for best accuracy.

Electric fans will save MPG's over a stock fan because of the reduce drag on the engine. The fan is ran by the engine via pulleys so the air resistance create drag on the engine (just like running the A/C does since it's running the compressor) so removing it and putting in electric fans will net you better MPG's. Electricity is free via the alternator but mechanical power comes at a cost. It's not a huge difference though, so before everyone ditches their fans and puts in electric ones it's hardly noticeable.

It's not uncommon for those with rock crawlers to install electric fans for increased air flow at low speeds, since the engine doesn't produce enough RPM's and fan speed to cool off the engine.

Not exactly. When the electrical load presented to the electrical system is increased, the load on the Alternator is also increased. That means the load placed on the engine to drive the Alternator also increases. This increased load will cause the engine to burn more fuel.

Whether this increased electrical load presents as much of a load to the engine as driving a thermostatically controlled clutched fan, depends on a bunch of factors.

Without running tests to measure fuel consumption exactly under strictly controlled conditions for both types of cooling fans, there are just too many variables to say conclusively which is most efficient in a given application.

 

[absalom]

Electric fans will save MPG's over a stock fan because of the reduce drag on the engine. The fan is ran by the engine via pulleys so the air resistance create drag on the engine (just like running the A/C does since it's running the compressor) so removing it and putting in electric fans will net you better MPG's. Electricity is free via the alternator but mechanical power comes at a cost. It's not a huge difference though, so before everyone ditches their fans and puts in electric ones it's hardly noticeable.

It's not uncommon for those with rock crawlers to install electric fans for increased air flow at low speeds, since the engine doesn't produce enough RPM's and fan speed to cool off the engine.

Please see link.

 

[gamefreakgc]

Well, everyone's got a different opinion. Mine is based of people with the older 22RE and 3VZ-E engines that showed slightly increased MPG's with electric fans. (and much cooler temperature at trail speeds) I suppose each engine is different and may have different results. A Mazda RX-7 doesn't seem to gain much but then again, the engine is made much differently than an SUV. Those are built for speed and performance more than a 4Runner, while ours are made for torque and maximum cooling efficiency while towing and other things.

 

[absalom]

Well, everyone's got a different opinion. Mine is based of people with the older 22RE and 3VZ-E engines that showed slightly increased MPG's with electric fans. (and much cooler temperature at trail speeds) I suppose each engine is different and may have different results. A Mazda RX-7 doesn't seem to gain much but then again, the engine is made much differently than an SUV. Those are built for speed and performance more than a 4Runner, while ours are made for torque and maximum cooling efficiency while towing and other things.

If you read that article, you'll notice he discusses simple physics (among other basic STEM concepts) that have no specific relation to the Mazda. Electricity via the alternator isn't "free". Increased electrical load from the system increases the resistance to turn the alternator which eats up any parasitic draw on the motor gained by ditching the mechanical fan in the first place.

The article isn't an opinion piece. He uses basic science to show how ditching a mechanical fan for an electrical fan won't increase MPG or result in an appreciable power gain.

Cooler temperatures aren't desired in any motor. The key temperature we should all be after is the proper operating temperature as designated by the manufacturer of the motor. If a rock crawler, or any other driver who drives at low speeds, is unable to maintain this proper operating temp, than there's a flaw with their current cooling system. Either the shroud is missing/damaged, the fan is damaged, air in the radiator, etc. But a properly set up mechanical fan as designed by OEM, will be able to cool the vehicle no matter how slow the driver is going.

Also, keep in mind, any perceived fuel savings realized by converting to electric fans disappear after ~25 mph. Vehicles automatically disengage their fan clutches/turn off fan relays, once they surpass this speed. So any drag from the fans is removed from the equation at speed.

 

[02SE]

Well, everyone's got a different opinion.

What I stated isn't an opinion.

 

[nissanh]

Yeah, an electric fan still draws a current and slows down the engine. But my point was having two fans in front of the condenser as an added cooling method to cool the condenser. You can find an extra fan on Lexus SUV's (sorry don't remember the model), so I wanted two fans to get a better cooling. I was also worried about hot weathers across TX in the summer. That was my first cross country drive with a heavy load in the month of August.

Nascar's have the mechanical fan removed and an electric fan in place. This too explains the drag from a mechanical fan.

Ever since I moved from West cost to south east, the MPH dropped to 17.5 from nice 20-21.5 MPG. The only change I did was getting gas from a different state and fans in front of the AC condenser.

I'll check the MPG in the coming weeks and will report.

 

[absalom]

When you say drag, are you referring to the parasitic loss caused when a fan clutch is engaged?

Fear not, if your OEM cooling system is in working order, your truck will be able to easily handle the hottest of Texas summers. Besides, how much time do you really spend below 25 mph?? Also, how were your electric fans hooked up?