I didn’t used to believe it. Sure all the good gas mileage cars were always crap. But I figured that was because the hippies never had money to spend on them. But over the weekend I upgraded my 1999 Jeep Wrangler with a high-flow cloth air filter, and an electric cooling fan. The results in both performance and fuel economy astound me. The Jeep has 110k miles on it, and was getting 14 city 19 Highway, down from when it was brand new and reported 16/24. After the upgraded I’m now getting 31 highway and 24 city.
At this difference in fuel economy the 50 mile each way commute from San Jose to San Francisco is going from using 3 gallons of gas to using 2. At a price of $2.50 a gallon (which would be cheap) I save about $5 a day on the commute. The upgrades cost:
- Electric Cooling Fan $30
- Thermostat for Cooling Fan $35
- Paper Air Filter $25
And they took about 3 hours to install. I should recoup the hard cost of this upgrade in two months of commuting.
The Jeep is also more fun to drive. By removing the fan which is driven directly off the engine I removed about 5 pounds of weight from what is essentially the engine shaft. Previously when the engine revved it had to accelerate this mass, plus the resistance of the air. This robbed several pound feet of torque from the engine. The Jeep has about 172 pound feet of torque at the engine, so even a small increase can be quite large. The fan clutch on the Jeep is designed to engage at 7.4 pound feet, which implies the drag of the fan must be in excess for that number, so just assuming 8 pound feet, that works out to be 4.5-5% increase in torque, which translates almost directly to a 5% decrease in your 0-60 time.
I was able to get slightly better results than I might have with this mod, by reducing the idle from 1100 RPM’s to 900 RPM’s which should save about 20% at stop lights, and while sitting idle.
Overall I remove 17 pounds of stuff from the vehicle which should also be good for the car, and I lowered the operating temperature from 210 degrees to 208, which shouldn’t drastically change things, but before the car ran a bit hot in the summer so this should help.